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Drought: Introduction
by Olivier Filippi
Extract taken from The Dry Gardening Handbook published by Thames & Hudson.
Drought has always been considered as a limitation for gardens. We have all been influenced by the temperate climate garden model, in which thriving shrubs and lush perennials surround a perfect lawn. Every month, gardening magazines make us dream of superb gardens, generally in northern Europe. Beautiful photographs in gardening books promote an image of rustic scenes, where roses and clematis grow intertwined. Yet in areas with a mediterranean climate these ideal conditions are a dream that can never be fulfilled. Instead of gentle light we have brutal sunshine; instead of rich soil we have the stony garrigue. The drier the climate, the harder it seems to make a garden. It is as if we are engaged in a ceaseless battle against a hostile environment.
Nevertheless, dry climates offer extraordinary gardening possibilities. Paradoxically, thanks to a long tradition of a passion for gardening and botanical research, it is in England that the largest collections of drought-resistant plants have been amassed. These plants are jealously cared for as if they were precious rarities, grown in raised rock gardens to ensure perfect drainage and sometimes cultivated under glass to protect them from an excess of winter wet. Garden-lovers flock to the Royal Horticultural Society's famous garden at Wisley, south of London, to admire a sophisticated rock garden re-created under glass. Its treasures include plants that often no one bothers even to glance at on our Mediterranean roadsides – Rhodanthemum from Morocco, Erodium from Greece or Sideritis from Turkey. While English plantsmen pride themselves on their collections of plants for dry conditions, gardeners further south are desperately watering their lawns, but achieve nothing more than a mediocre imitation of an English garden.
Rather than drought, it is often the misguided use of irrigation that limits the range of plants in mediterranean gardens. Many dry-climate plants are in fact easy to grow if we respect the conditions of their native habitat, but become extremely capricious as soon as we try to water them in summer. The cistuses of the garrigue, the ceanothuses that cover the hillsides of California or the capers that billow down Sicilian cliffs quite simply cannot tolerate the combination of heat and moisture. Irrigation during our blazing summers generally proves fatal to them.
If you water your garden during the hot weather you will never be able to grow the full range of plants adapted to the mediterranean climate. The beautiful Salvia candelabrum will be nothing more than a fantasy, the magnificent Fremontodendron covered in golden flowers won't stand a chance. Don't bother even to dream of the vibrant blue of Lithodora fruticosa or of the soft, silky pink flowers of Ebenus cretica: irrigation will kill them just as surely as a powerful dose of herbicide. Automatic watering systems are one of the worst inventions of the modern mediterranean gardener. You may think you are making life easier while in fact all you're doing is limiting the range of plants that can survive in your garden. Without realizing it, you are helping to reduce the plant palette to uniformity. In region after region, gardens end up all looking much the same, having lost the individual identity that is linked to their particular climate and soil conditions.
What will happen if you stop watering? Well, yes, the plants that need water will die, one after another. So what will be left? Everyone dreads the idea of a miserable-looking garden, where dusty borders contain only a few spiny plants, and wretched shrubs eke out a meagre existence. We feel instinctively that water brings luxuriance and variety, and that dryness restricts our gardening possibilities. Yet exactly the opposite is true. Most gardeners are unaware that the natural flora of mediterranean-climate regions is a lot richer than that of temperate regions.
Olivier Filippi's book (translated from the French by Caroline Harbouri) is available from Amazon.co.uk.
A Selection of Articles from The Mediterranean Garden
The word "drought" has two slightly different meanings. On the one hand, it is often used to refer to the hot dry summer period in mediterranean-climate regions when there is no rainfall, which may last for three or more months. This kind of drought is regular and expected. On the other hand, it refers to an unusual state of dryness caused by insufficient rainfall or even a complete lack of rain during what is normally the wet season.
It is hard to predict how climate change will affect mediterranean areas, but we may very well have to face hotter, drier or longer summers. We shall thus need to be increasingly careful about our use of water in the garden.
This has been the subject of many articles in the journal, by authors from different parts of the world. We are reproducing a selection of them here.
Katherine Greenberg, writing from California, stresses what a precious – and limited – natural resource water is. Read article.
Trevor Nottle writes from Australia, encouraging us to change our attitudes to drought, as well as our gardening practices. Read article.
Isabelle Greene, once more from California, reminds us of a crucial point, namely that we need to work in harmony with natural systems in order to be prepared for years of exceptional drought. Read article.
In her own garden on a Balearic island, Heidi Gildemeister, the doyenne of waterwise gardening, demonstrates in practice that it is possible to have a beautiful and green garden which requires very little water. Read article.
In Italy, the late Piero Caneti takes a close look at plants that need little water, recognizing that the period of summer dormancy which many Mediterranean plants undergo in order to protect themselves from drought makes some of them less ornamental in the garden during the hot months. Read article.
The late Joan Tesei examines the effects of the drought of 2003 on her garden, also in Italy. Read article.
(For obituaries of Piero Caneti and Joan Tesei, see TMG 36 and TMG 41 respectively.)
From Israel Ran Pauker provides a new Decalogue, in other words a series of ten commandments for waterwise gardening that he implements on his kibbutz. Read article.
Finally, Brian Chatterton, an Australian living in Italy, gives us a timely reminder that water is vital for food production and discusses dry-climate farming practices. Read article.
Water, a Limited Resource
Water is essential for life on earth, and it is a limited and valuable resource in the mediterranean climate regions of winter rain and long dry summers.
Historically, nations with water had power, and that is still true today. In the last century elaborate systems of dams and water distribution facilities have made water available on a scale that was unimaginable in the past. Even with these advances, demand exceeds supply in many areas where water supplies are stressed by human activities. Humanity is facing a shortage of fresh water due to population pressures, droughts, depleted wells and aquifers, salt water intrusion and pollution.
Accessible fresh water in rivers, lakes and aquifers is less than one-tenth of one percent of the earth’s water, and this supply is decreasing. Water is being pumped out of the ground faster than it can be replenished. Agriculture and industry account for ninety percent of all water use, and less than ten percent of water is available for households. This leaves precious little water for developing and maintaining gardens.
The world’s leaders and over 10,000 delegates met in South Africa in August 2002 for the United Nations Conference on Sustainable Development, in order to consider ways to balance protection of natural resources with population growth and development. Recommendations for water use included conservation through improved delivery systems, more efficient irrigation methods, planting of drought- and salt-tolerant plant varieties, and better monitoring of growing conditions such as soil moisture levels.
According to Mark Malloch Brown, administrator of the United Nations Development Program, “When you approach sustainable development from an environmental view, the problems are global, but from a development view, the front line is local, local, local.” The message of the Mediterranean Garden Society is more appropriate than ever. We can make a difference by promoting waterwise gardening in harmony with the climate and available resources.
Plants native to the mediterranean climate regions thrive with winter rain alone, and there is a wealth of native flora to choose from. Traditional Mediterranean gardens show us the way to design gardens for the pleasures of outdoor living using paving to take the place of water-consuming lawns, trees and structures for shade, drought-tolerant plants, and a small pool or fountain. We are only limited by our imagination.
Drought in Australia: Changing our Thinking
by Trevor Nottle
From The Mediterranean Garden No 34, July 2003
‘Drought-proofing Australia’ has been much in the headlines and in conversations during the last 12 months as severe water shortages in our river systems and storages have reduced the supply to critical levels. It has brought to the fore our heavy reliance on relatively cheap access to a commodity that is taken as an essential to our lifestyle, as much as it is to our industries and future prosperity. But is it appropriate to name a regular feature of our climate – a long, hot dry period – a drought? After all, a drought is a period of time during which expected rain does not fall. If this absence of rain is a regular annual feature of climate, can it properly be called a drought? It seems that it would be more accurate (and sensible) to acknowledge that such circumstances are indeed not drought but simply a natural condition: one with which we should learn to live and work. Certainly there are periods when expected rain does not fall. At such times the word drought might best describe the situation if it is an uncommon phenomenon. But what if ‘drought’ has been a regular occurrence seven years out of ten over a long time span? Is this really drought or just the usual dry season?
Our cultural background has coloured our thinking and fogged our perception of the places where we live if we view the yearly (= seasonal) ‘dry’ as a time of drought. In my view it is not. If it is thought that we can ‘drought-proof’ Australia, then surely we are wishing it were not what it is, wanting it to be made less like it actually is and more like somewhere else – presumably a place where summer rains are more regular and reliable. Proposals to turn the rivers inland, to flood Lake Eyre with sea water to make an inland sea, to pipe Ord River waters thousands of kilometres across central Australia, to tow icebergs from Antarctica to the Southern coasts, to seed clouds and create clouds by generating wind patterns: all these have been suggested as solutions to the perceived drought problem. However real or foolish these and other proposals may prove to be, they are sure indicators that, as much as any other factor, it is our perceptions that are the true problem we have in coping with and accepting the climate in which we live. Coming to terms with the place that we occupy and use is an ongoing process which many are just beginning to realise is an issue that confronts us all. To address this issue we gardeners have some significant resources to call on.
First, we can draw on the historic resources we have in the living collections of plant material found in our nineteenth century botanic gardens. Many of the trees and plants which form the backbone of these gardens are proven ‘doers’ in our climate, particularly those found in old regional botanic gardens and community parks. They grow well without us having to try to ‘doctor’ the growing circumstances with supplementary irrigation every summer. Although most of the major botanic gardens now rely heavily on irrigation, a great many of their nineteenth century acquisitions are very drought-tolerant and often out of the reach of the sprinkler systems. So at a time when many botanic gardens are redefining their relevance as scientific and educational institutions by promoting visions of ecological imagination, it is opportune to suggest that they have a primary role to play in rekindling the appreciation and use of the plant heritage they conserve.
Second, we can use the impetus provided by the water ‘problem’ as a stimulus to new thinking about garden design, plant use and sustainable relationships between our lifestyle and the places in which we live. Think of it this way: at present many gardens consist of plants that are, in the main, highly water-dependent. When faced with the need to save water, the most acceptable solutions are twofold: use technology to apply water more cleverly, and increase the water-holding capacity of the soil by using mulches and chemical saturants, and by planting a few drought-tolerant plants. A greater saving could be made by eliminating or minimising the area of lawn in a garden, but that’s a harder decision to make. How much better things would be if, instead, we turned our thinking (and planting) on its head by beginning with a backbone and fill of plants that need little or no summer irrigation and employing high water use plants in only a few strategic locations such as the vegetable patch or cut flower garden.
Third, we can scan the pages of the Australia’s Open Garden Scheme Guide for reassurance that there is garden life after coming to terms with our local climate. What these gardens show is that variety is not confined to water-dependent gardens, any more than it is by green creativity or omnipresent floral powerhouses. A few examples of the developing shift to gardens that not only accept but embrace the climates in which they are made are found in William Martin’s garden, Wigandia, on a scoria cone at Mt Noorat, Virginia Kennett’s garden on Mt Osmond, Fiona Brockhoff’s marine garden on the Mornington Peninsula, Margot Knox’s mosaic garden in suburban Melbourne, George Seddon’s garden in Fremantle and Barbara Maund’s garden in Castlemaine. The extent of this far from complete list suggests a growing tide of experience and maturity that relates garden-making to the local environment, and an increasing number of gardeners and designers working with their locale rather than trying to force changes on it.
Fourth, we can look to our tertiary education institutions to take on board the challenges of making the transition from reliance on supplementary irrigation to sustainable design and plant selection through the courses they offer. In schools of landscape design, urban planning and environmental management, these issues are beginning to exert a profound influence on curricula. Students, whatever their ages, should be expecting leadership and fresh thinking here.
The Torrens Valley TAFE State Centre for Horticulture, based at the Urrbrae Education Centre on Peter Waite’s historic Urrbrae estate in Adelaide, is developing a programme for sustainable water use to be offered in 2004. This initiative is the first in Australia that will address the emerging industry based on the sustainable use of the resource. It will complement other programmes that also take sustainable water use as a focus: garden design, landscape construction, nursery operations, parks, gardens and turf management, and environmental management. The campus is being developed as a demonstration site for students and staff which is also accessible to the general public. Living Plant reference collections of important drought-tolerant and xerophytic plants are being established with an emphasis on those that have garden and landscape value. The plant collections are being deployed in a number of gardens that illustrate design and planting ideas suited to the mediterranean-type climate of the area. As well as Australian native plants, the gardens also showcase plants from the five main mediterranean climate zones of the world.
The horticultural industry says it provides whatever its customers demand, so it is up to all of us – academics, designers, creators and gardeners – to review our requirements in view of the changing circumstances and to make appropriate moves that will enable sustainable, creative gardening for the future. Already there is a groundswell for change among industry members. Consumers – that is, gardeners – have shown strong support for nurseries which have ventured into supplying plants that will grow ‘dry’, thus making possible the adventure we now share as we discover how to make gardens that are sustainable and creative within the climates experienced where we live.
There will be those gardeners who will want to know whether this phenomenon is a trend, and how long it will last. More importantly, they will want to know what is coming next. Unfortunately, there can be no simple answers. No doubt new trends will be imported and given a run by some gardeners and designers – and who can say which will be found to be fashionable? But this particular concept of sustainable garden making has little to do with mere fashion. We need to be more confident, creative and self-sufficient than that. Creative gardeners and nurseries will concentrate instead on forging through their own experiences an approach to gardening that takes a long-term view rather than getting caught up in the ever-spinning wheel of the fashionistas.
I suggest that our Anglo-European history fogs our thinking about how to live and garden in Australia. What is needed is a new platform from which to step forward. For me this means deliberately trying to move on from the gardening traditions we have largely retained since the first settlements here. Understanding that we are not living in some other cooler, wetter place is important, but if this cultural baggage is to be successfully offloaded something else is needed to grow in its stead.
There is an increasing diversity of plants available well suited to the different climatic regions of our country. The water ‘problem’ seems unlikely to change. A gallery of creative Australian gardeners exists – our very own pantheon if you like, comparable to those found in the UK, the USA or Europe. We are coming to value our collective knowledge and experience. Australia’s Open Garden Scheme makes these things explicit through its leadership in opening a wide range of excellent Australian gardens and acknowledging the gardeners responsible for them. It provides unparalleled access to the developing vision of gardens that grow out of the environment in which they are created. And this is an opportunity for all gardeners that is just too good to miss.
Mediterranean Gardening: The Benefits & Challenges of Slim Rainfall
by Isabelle Greene
From The Mediterranean Garden No 22 October 2000
Enjoy the pleasant dry atmosphere and pungent sturdy plants of Mediterranean areas! These plants are not water wimps: they live and have their being in their adaptive strengths. That same reduction of moisture that frees Mediterranean areas from insects, spoiled picnics or cancelled games, and generally produces the bright, benign, most pleasantly habitable areas on earth has also produced this special breed of plants. Enjoy them for their unique beauty and special characteristics.
Therefore, you may well want to design your garden featuring this palette of suitable plants, and will thus avoid the pitfalls of a garden that – heaven forbid! – tries to mimic wetter places on earth. A garden whose life depends on transporting copious quantities of water from somewhere else is not a garden of repose but a garden of struggle. It becomes ever more evident that our planet requires us to cease our quest to overcome natural systems – depleting them by struggling against them. We need to understand the benefits of working in concert with natural systems.
Beneath the threshold of the appropriate planting palette, lies another threshold more particular to many Mediterranean regions. The slight precipitation in these areas is not by nature spread out in even sequences, but occurs in mountainous lumps, with gaps in between. Several years of plentiful rainfall seem to be endless abundance, and will bring about a forgetful population. Municipal systems have reserve supplies, and yet – when an entire state goes dry for six or seven years – the unavoidable facts will come home to roost with every individual.
Keeping this extra understanding in mind then, always prepare mentally for a cyclic super drought (several years’ duration at a time).
- First and foremost: design it that way. I once crafted a garden for some seasoned Californians who had weathered several of our dry cycles. They stipulated that the plants inside their small inner courtyard could be year-round green and thirsty, but that the balance of plants on their property consist entirely of natives. This we did very successfully, even including a Zen-like garden with sycamores as trained Bonsai, creeping Manzanita carpeting the ground, and rock. The garden weathered very well, even over the long term.
- Secondly, have an emergency plan in mind (when push comes to shove and there is no more water in sight): decide what is to be preserved, and what is to be let go – and be organized about it. Obviously, your mature majestic trees and specimen shrubs need priority; give them the staying power of a drip watering system to stave off possible stress. Smaller thirsty plants, especially lawns and annuals, are minor in cost and deserve rethinking about anyway once the dry cycle is completed.
- Finally, use each of those cycles to balance your garden more towards an appropriate direction. You and your garden deserve to live stress-free!
Not All Plants Are Equally Thirsty
by Heidi Gildemeister
From The Mediterranean Garden No 8 Spring 1997
As never before, Mediterranean gardeners are faced with lack of water, not always due to summer drought. This may take newcomers by surprise. For my own garden, water being scarce has become a way of life. In summer, our water tank invariably runs dry with many weeks of drought to go. I remember how concerned I was when first faced with this uncomfortable situation and how I cried over the inevitable losses. Meanwhile, I have become confident since I know that my garden will survive. It has done so year after year, turning lusher as time goes by. An array of recipes lets it come through dry summers. Grouping plants according to their water needs is one of the prominent ones.
You will achieve important savings in water if you divide your garden into areas with high, moderate and low water needs. In each of these three areas you group plants with similar moisture requirements and rearrange those areas where drought-tolerant species have been planted next to thirsty ones. By giving your plants the right amount of water, you use the precious liquid where it is beneficial and avoid all unnecessary waste. You can also try to reduce the area with a high water use, especially if it is not essential to your garden. These simple guidelines, sometimes called hydrozoning, are worth gold to gardeners who have to make do with little water.
Many gardeners group their plants by leaf texture and flower colour; they deliberate on height and the flowering period or enthuse about variegation. The specific quantity of water required by each is not always considered. However – even if water were not scarce – this is a crucial aspect.
Plants are frequently irrigated whether it suits them or not – maybe even with the thought ‘the more the better’. But irrigation adversely affects those plants which prefer dry summers, for example the Mediterranean ‘greys and silvers’ or a range of Californian natives. These plants enter dormancy over summer and should be allowed to do so. But when waterlogging forces the air out of the soil, they asphyxiate as their unoperational roots rot.
On the other hand, bear in mind that, contrary to the above, plants such as Canna indica or angel’s trumpets (Brugmansia), which come from regions where it rains in summer or year-long, continue absorbing water over summer. They will only thrive if given generous supplies
When you divide your plantings into areas, remember that certain good-humoured plants tolerate life in high- or low-watering zones alike – as long as they are planted according to their requirements. Abelia and Escallonia, for example, favour dappled shade and that is where they demand the least water. Other plants are less resilient and require specific doses. Providing plants with the water they really require promotes their health and is an important step in avoiding disease.
When you are considering grouping plants according to their water needs, remember that those which over the years have been given lavish watering (while in fact they needed little) cannot be weaned from one day to the next. Their roots need time to adapt to foraging for water on their own – which may require two or three seasons.
Finding out the quantity of water that each plant really needs may call for a bit of research. Often experience helps: you know, for example, that lavender, rosemary and thyme are native to the Mediterranean where summers are dry. So why water them? My book, Mediterranean Gardening, A Waterwise Approach, lists several hundred plants which survive dry summers.
Often it is felt that a rich picture results only from plants which require, or are given, lavish watering. But this is not so. In the garden that I tend, watered and unwatered zones are alike in their colourful exuberance. It all depends on the right choice of plants which will give their best as long as they grow under conditions that suit them well. (This may mean sun or shade, protection from wind, above all generous mulching and well-draining soils.) Visualise a bed of Mediterranean climate plants such as Artemisia, Ballota, many Cistus, Coronilla, Euphorbia, Halimium, Helichrysum, Hypericum, together with iris and countless sunny Cape bulbs. They look as good, sometimes even better, than thirsty plants with a high water use and, closely planted, give your garden a luxuriant, evergreen cover.
Even if one has all the water in the world, grouping the plants according to the water needs benefits the garden. This so-called hydrozoning facilitates, for example, the installation of watering equipment, since it is difficult to water correctly areas where plants with high and low water requirements live next to each other. Where feasible, all watering equipment should be installed before planting. Thus you know how far water reaches and can choose plants accordingly. Less expensive and easier to maintain, such gardens suit those who have little time at hand.
Three different groups are suggested, but your garden does not have to have all three. You may, for example, concentrate the water available to you on a small lawn (the high water area) and, to make up for such an ‘extravagance’, border this lawn with a no-watering area. You do not have to stick slavishly to the recommended areas. Design your groups to suit your water allowance, your own needs and those of your garden. The three water use areas which follow can be seen as an example.
The area with a low water use
This area needs the least water and suits a tight water budget. Here you use all those plants which do not require more than annual rainfall. However, apply additional water until newly planted vegetation has been established. Depending on the size of the specimen at planting time, this may mean a year or so. Remember that drought-tolerant plants require excellent drainage and good ventilation and that most thrive in sun.
Such plantings include a delightful variety of plants whose flowers and fragrance offer pleasure throughout the year. In my garden, I use for this section plants from all Mediterranean climate regions. Winter rain takes care of them and generally carries them through summer without further attention (remember summer dormancy?). Countless unthirsty plants such as Bupleurum, Coronilla, Ceanothus, Cotoneaster, Cynara or Ruta qualify to make up the non-irrigated section, for example, in a ‘natural garden’. Most herbs thrive in this area. Or take advantage of the native vegetation found locally and reintroduce wild flowers. None of them requires summer water. This area could, but does not have to, be situated furthest from the house. Plants on the borderline of your garden need not be as manicured, since mostly you see them from a distance. Should you desire a formal approach, clipped cypress, myrtle and lavender cotton offer themselves.
The area with a moderate water use
The second group includes those plants that need more water than rainfall supplies, but not much more. Depending on the conditions your garden offers and the plants you have chosen, this may mean (in the hottest months) a once to twice weekly watering. In my own garden, I fare well with a weekly summer watering for this zone and maybe an additional application after drying winds. Your own observation will help you to determine frequency and quantity for your own garden.
Many plants you may want to grow in this second group do not come from a summer-dry Mediterranean climate and require watering in summer (Abutilon, Fatsia, Fuchsia, Hebe, Hosta, Phygelius). Their healthy growth and attractive flowers do not lag behind those plants which demand ample supplies. Closely planted and generously mulched (to retain humidity in the soil), they will present a cheerful picture which may provide a link between a natural garden area and a thirsty, water intensive zone.
The area with a high water use
In this water-intensive area you grow plants which require the most water. These may come from tropical lands or from regions with summer rain (Begonia, Camellia, Hibiscus rosa-sinensis, Hydrangea). It may also mean a lawn of moderate size, thirsty annuals, containers with exotics or a vegetable garden. Place your cherished high water plants next to the lawn and water them together with it for an intimate, luxuriant scene.
To take advantage of every drop of water, plant closely, mulch generously, and place where the least evaporation through wind and sun occurs. Diminishing the size of this zone trims down your water bill effectively. But whatever you decide on, use the water at your disposal how and where it will give you most joy.
Problems of Acclimatisation: Drought
by Piero Caneti
From The Mediterranean Garden No 19, Winter 2000
We all know that the periodic total absence of rain is one of the characteristics of the Mediterranean climate. Indigenous plants have adapted to this, modifying their organs through the ages to reduce transpiration, or the loss of moisture. This explains their appearance: thorns instead of leaves, smaller and hardier leaves. However during the dry season trees and shrubs show, if not real suffering, at least a certain discomfort as their leaves lose their shine due to their suspended development while they await the September rains. Herbaceous plants, having in fact concentrated their production of flowers and fruit in the spring, die in the summer, thus entrusting their reproduction to their seeds, or they dry up completely, greening the land again only when conditions become less prohibitive.
It is easy to understand why the phenomenon of drought still preoccupies Mediterranean gardeners who must decide whether to face the problem as though it were a curse to be exorcised by the only means they know – water – or whether to adapt to the inevitability of things. The two approaches are diametrically opposed: the former is certainly the riskiest, in that it stems from the assumption that water, whether on the surface or under the ground, is an inexhaustible resource available in vast quantities, while the latter decries the dangers of uncontrolled use of a resource that is precious for humanity and calls for a change in growing techniques, ultimately bringing the aesthetics of the garden into line with the hard facts of life.
During the last ten years, the selection of one or other of these methods has lost the connotation of free choice, if ever that existed, acquiring a compulsory character, even if not everyone has become aware of this. The problem has now become a burning issue, since the climate changes currently taking place have led to the alternation of abundant rains with periods of drought which, in the Mediterranean climate zone, are compounded by the already existing aridity. According to scientists, the ‘tropicalisation' of the Mediterranean basin, due to the rise in the average temperature by several degrees, will bring about the desertification of vast areas in the south. In the spring and summer of 1998 we had a glimpse of what could happen. After an autumn with rains of normal intensity an equally rainy spring was expected, but instead the climatic conditions were abnormal. At our observation post located in the sub-littoral zone, the winter brought sporadic falls in temperature reaching –7 °C but was basically mild, so that plants not only did not reduce their vegetative activity but in fact increased it due to the favourable levels of moisture in the soil. In cases like these, there is usually a sudden and precocious spring, but this did not happen because the consistent rains of April and May did not come. As is well known, the month of May is crucial for plants in the Mediterranean climate, since it is the month of the fastest growth in preparation for the hardships of summer. During May the water requirements of plants are at their greatest and if it does not rain now this not only means that there will be five dry months, but also that the vegetation will be unable to complete a most important part of its normal biological cycle to survive these months. Having recourse to an early input in water is no solution, because the soil would require an enormous water supply to recharge it in depth with the resources which have already been consumed by the precocious growth of the plants. In other words, even with the most sophisticated technology, it is not possible to compensate for lack of rain in the preceding months. Even if the physical structure of the land were to allow it to absorb large quantities of water in a short time, which is plausible only if the soils are naturally porous and deep, the daily presence of the sun would cause thermal imbalances and hence the proliferation of fungi and parasites that are deadly to plants.
It was therefore decided, in the acclimatisation garden where these observations were being made, not to intervene even with emergency irrigation on all plants established there for at least four years, to avoid fertilisers and to maintain a substantial layer of mulch around each individual plant, whether isolated or in groups. As has been said, the garden is located in the sub-littoral zone at an altitude of 400 m on land of volcanic origin, in other words with a not very acid, soft, fresh and deep soil. In order to avoid burdening the experiment with obvious results, indigenous and naturalised plants were not taken into consideration, and neither were plants of the Mediterranean climate zone and the most common palms, known for their great resistance to drought. In this respect it should be remembered that in 1986 these withstood a period of continuous lack of rain lasting all of eighteen months!
We believe it to be of interest that we limited our test to two groups of plants with a single characteristic in common:
- plants coming from geographical areas with climates that are different from the Mediterranean climate;
- plants (even indigenous and coming from Mediterranean climate zones) that in the dry summer season assume a disappointing aspect from an ornamental point of view.
Drought-resistant plants coming from regions whose climate differs from that of the Mediterranean:
Trees
Firmiana platanifolia
syn. F. simplex
Shrubs
Abelia x grandiflora
Brugmansia suaveolens
Buddleja davidii nanhoensis
Caesalpinia gilliesii
Camellia japonica
Camellia sasanqua
Caryopteris x clandonensis
Chaeonomeles japonica
Chimonanthus praecox
Colletia hystrix
Colletia paradoxa
Cordyline australis
Cotoneaster dammeri
Cytisus x praecox hybrids
Cytisus scoparius hybrids
Cytisus spachianus (Genista
x spachiana)
Echium candicans
Elaeagnus x ebbingei
Erythrina crista-galli
Eupatorium ligustrinum
(Ageratina ligustrina)
Indigofera heterantha
Jasminum humile
Lantana camara
Lantana sellowiana
(L. montevidensis)
Lonicera fragrantissima
Lonicera nitida
Mahonia aquifolium
Mahonia x media ‘Charity’
Osmanthus x burkwoodii
Osmanthus delavayi
Osmanthus heterophyllus
Photinia x fraseri ‘Red
Robin’
Phyllostachys aurea
Phyllostachys mitis (P. edulis)
Pittosporum tobira
Prunus laurocerasus
Prunus laurocerasus ‘Otto
Luyken’
Rhaphiolepis indica
‘Springtime’
Rhaphiolepis umbellata
Sarcococca humilis
Spiraea cantoniensis
Yucca (all)
Climbers
Abutilon megapotamicum
Akebia quinata
Araujia sericifera
Campsis radicans
Clematis armandii
Clematis montana
Dregea sinensis
Macfadyena unguis-cati
Ipomaea indica
Jasminum nudiflorum
Parthenocissus
quinquaefolia
Parthenocissus tricuspidata
Passiflora caerulea
Solanum jasminoides
Trachelospermum
jasminoides
Wistaria (all)
Drought: Survivors and Non-Survivors
by Joan M. Tesei
From The Mediterranean Garden No 36, April 2004
Though I have gardened in the Maremma region of Tuscany for almost thirty years and have become inured to our hot, dry summers, I had never experienced such a devastating drought as that of last summer. I keep lists from year to year of seasonal flowering, resistance to cold and of almost anything else which interests me or seems in any way unusual. The last drought survival list I made was in 1993, a year in no way comparable to 2003 for the length and severity of the dry season.
Some of the effects of last summer’s drought were already apparent half way through August and not only in the garden but in the surrounding macchia, most obviously in the small local maples, Acer monspessulanum, whose leaves had turned a premature brown rather than their usual autumnal yellow. I feared they might actually have died but was unable to verify this as I’d broken my knee and was on crutches.
The entrance to my garden runs beside an untrimmed hedge of Strawberry bush, Arbutus unedo, which, as the summer wore on, began to look ever more dilapidated, many leaves falling and others withering along the edges. Normally this hedge is never watered but with the danger of losing it altogether appearing imminent, an exception was made and each of the seventy plants was doused with a 12-litre bucket of water. Though this undoubtedly saved the hedge it did not make it look much better so even more drastic action was called for. Towards the middle of September when it seemed that rain could not be far away I cut the entire hedge back to a height of three feet, a procedure not without risk for, unless autumn turned out to be mild and rainy, the shrubs would probably not have time to put on and ripen enough new growth to enable them to withstand the winter. On the other hand waiting until the spring would mean coddling them through the following summer, not a particularly enticing prospect.
Between the hedge and the entrance to the house is an unwatered bank planted with a mixture of local shrubs, bay, laurustinus, myrtle, lentisk and Rhamnus alaternus. Of these only the lentisk and the Rhamnus came through completely unscathed. The others all suffered from browning of their leaves, and, in some cases, from dieback of entire branches. There seemed to be no particular pattern, one plant standing proudly up to the drought while its neighbour wilted visibly. I can only assume that the survivors had managed to squeeze their roots further down between the rocks to a patch of damper soil.
Another part of the garden is backed by a holm oak hedge, Quercus ilex, probably the most common native plant and therefore, I had thought, one best suited to the local climate. Nonetheless large patches of the hedge turned brown. I left it untouched over the winter partly for lack of time and partly to see which branches resprouted in the spring; alas, I have a good deal to cut out in the next few weeks.
The plants mentioned so far are all in areas which are never watered and where some losses were probably to be expected. However even within the areas covered by driplines there were casualties. The escallonias in particular were hard hit and looked so miserable that I cut them down to ground level, not without some misgivings, as one or two, though not in any way Mediterranean plants, were among the oldest and most wide-spreading plants in the garden. Happily all quickly produced new shoots, though it will be a long time before they attain their original girth. Some of the newly planted young shrubs, including certain Ceanothus and a collection of Cistus from Olivier Filippi, also succumbed despite extra care in the form of protective mulches and regular watering. Others, surprisingly, survived, among them several varieties of Clematis viticella, thus confirming my view that these are not only beautiful but also the best clematis for Mediterranean gardens.
So far I have only mentioned plants which, to a greater or lesser degree, were injured – a rather one-sided approach, given that certain plants came through totally unscathed. Not a single rosemary suffered, not even those planted on a rocky bank near the entrance and a long way from the garden itself and any form of care. Cneorum tricoccon, a small shrub from the Western Mediterranean, was a winner. Though modest in appearance, like box it submits to any amount of clipping and can be used for the same purposes. Its flowers are nondescript but the seedheads attractive and, above all, it is apparently totally resistant to drought. I have to add that at the Margheriti nursery in Chiusi, I was told I was the only customer ever to have bought one! Perhaps prospective customers will now change their minds.
I have no complaints of shrubs from other Mediterranean climate areas, for none collapsed or even showed signs of doing so. Romneya and Fremontodendron flowered in their usual way. A couple of newly planted Geraldton Wax Flowers, Chamelaucium uncinatum, doubled in size, while Westringia, Eremophila and Coleonema held their own without losing a single leaf.
Another outstanding group consisted of five seedlings obtained in 1996 from Bert Wilson’s nursery near San Luis Obispo: an Arbutus menziesii, an Arctostaphylos manzanita ‘Dr. Hurd’, a Heteromeles arbutifolia, a Rhus integrifolia and a Californian live oak, Quercus agrifolia. He told me to plant each in a large hole near an oak tree (for the beneficial effect of the mycorrhiza), water them thoroughly and then forget them, instructions carried out to the letter though at the time I was not at all convinced that they would succeed. Now, nearly eight years later I have five large, flourishing plants, all seemingly quite impervious to anything our weather can throw at them. Are Californian chaparral plants tougher or is the mycorrhiza working its subtle magic? I simply do not know.
Ten Commandments for a Waterwise Garden
by Ran Pauker
From The Mediterranean Garden No 32, April 2003
The experience gained from the 40-year project at Kibbutz Nir-Oz, described in TMG 31, led me to formulate the following ‘ten commandments’ for waterwise gardening. You can create a waterwise desert oasis by obeying them – making adjustments for the particular conditions prevailing in your own garden, be it old or new.
- Plan ahead. Foresight and planning are the key to a waterwise garden that will satisfy expectations and suit the local environment, the amount of water available, and a feasible level of maintenance.
- Test your soil. A knowledge of the soil’s mechanical and chemical composition and depth is important for deciding whether soil amelioration is required and, if so, what form it should take. This information is also necessary for estimating water percolation rates, water holding capacity, conditions that will promote a deep, well-developed root system, soil nutrient levels and aeration. A knowledge of the mechanical composition is particularly important when the addition of ‘imported’ soil is planned.
- Irrigate in accordance with the plant’s needs.
- Supply precisely the right amount of water to the right spot.
- Every plant must receive its allotted amount of water (we want the plant to be fresh and healthy).
- Irrigation regimes, macro- and microclimatic conditions, nutrient application and various stresses – all these influence the plant’s water needs. The amount of water supplied should be adjusted to the plant’s ‘body language’.
- Use an efficient irrigation system. The irrigation system must be designed and operated in accordance with the basic rules listed in the previous item and the water emitters (sprinkers, microsprinklers, drippers) should be chosen and planned accordingly. Even when water is applied at fixed times, precise measurement of actual versus planned water expenditure is essential. This is the only way to detect problems in planning, flaws in the pipe system (leaks) and plant stress. The irrigation rate must be adjusted to the type of soil present.
- Collect the run-off. Both the topography and the infrastructure of the garden should be designed so as to catch as much as possible of the water flowing through the garden, including rainwater and water running off impermeable surfaces, as well as water condensing from air-conditioners. Instead of this water burdening the drainage system and running off uselessly into the sea, it could help replenish the groundwater, while contributing on the way to the soil water reserves accessible to the plant. Run-off water may also be caught in ponds for summer irrigation and to give pleasure.
- Use marginal water. Wherever technically feasible and safe, plants should be irrigated with marginal water – purified sewage water, grey water (run-off from bathroom showers, sinks and washing machines) and brackish water. The effect of the marginal water on plants, soil and groundwater should be tested ahead of time.
- Reduce the size of the lawn. The lawn is the garden’s biggest water guzzler, both because of its high consumption per unit area and because of the large area it occupies. Therefore the lawn should be confined to specific areas dedicated to sport, games or relaxation. For the rest of the garden one can turn to waterwise solutions such as shaded walks (paved or strewn with gravel or other material), shrubs and water-sparing ground cover plants.
- Choose the right plants. One should choose water-sparing plants well adapted to the climate and to the soil of the garden. Inappropriate selection will result in the plants displaying excessive sensitivity to climate stresses, the modern environment (air pollution, mechanical damage by individuals and vehicles), nutrient shortage and plant diseases and pests. A plant that is suffering needs devoted and time-consuming care, as well as abundant water and nutrient supplements.
- Mulch the soil. Covering the soil has the effect of moderating hot and cold temperature extremes at the soil surface, thus encouraging root growth. This leads to a better absorption of water and minerals. There is less of a tendency for a crust to form at the surface so water and gases penetrate more readily, and therefore run-off and soil erosion are reduced. The net result is that more water is available to the plant. In addition, organic mulch enriches soils that lack organic matter.
- Maintain the garden correctly. Weed control, limited dosing with nutrients, planting at intervals suited to the species, and other measures designed to optimise the growth conditions of the plant will improve its appearance without necessitating additional water. It is also necessary to check that the irrigation system is in good condition and operating properly. Adherence to commandments 1-9 for a waterwise garden will significantly reduce the cost of maintenance.
Drought – A Mediterranean Farmer’s Perspective
by Brian Chatterton
From The Mediterranean Garden No 37 July 2004
In Umbria we have recorded our wettest spring for fifteen years and memories of drought are quickly fading but my experience of farming in a Mediterranean climate in South Australia has taught me that drought is a constant feature of our zone and it will return.
The Mediterranean climate includes a hot dry summer as a normal weather pattern and I am reluctant to call this a drought. In fact a true drought here begins in winter and spring when rainfall is well below normal. We receive some strange looks from the holiday visitors in our village when we complain about lack of rain in April and May. “But the grass and the forest is so green,” they protest, without realising this growth is rapidly depleting the limited store of moisture in the shallow soil.
For the farmer summer rain is a nuisance. It interferes with the harvest of the cereals. Annual pastures lose their feed value and an early, false germination of the pasture legumes can weaken their ability to regenerate in autumn. For summer-growing crops rain is a mixed blessing as summer rain encourages the fungus diseases of vines and olives. These both benefit from a period of moisture stress to produce good quality oil and wine.
Drought evasion
Most of the traditional annual Mediterranean crops such as wheat, barley and lentils grow during the rainy season from autumn through winter to spring. They are, like so much of the Mediterranean flora, not particularly drought resistant but they are excellent drought evaders. They survive over the summer months in the form of seed. Drought evasion is an excellent strategy to adopt in a garden, as it is so much easier to work with the climate than to fight it. Annual plants grown from seed and bulbs, corms and rhizomes are all excellent drought evaders. However, a garden based completely on drought evaders would be a scorched desert in the height of summer.
Summer crops
Crops like vines, olives and the recently expanded sunflower crop grow in spring and on into mid-summer on the moisture accumulated during winter and spring. The degree of moisture storage in the soil is dependent on the soil type and depth. Clay soils will hold considerably more water than sandy soils but they have a higher “tension.” This means that most plants can extract only a part of the potential supply of water in the clay soil. The lack of soil depth is an obvious barrier to moisture retention on our Umbrian hillside. We struggle to grow trees that developed into enormous specimens in my grandfather’s garden in the Adelaide hills with almost identical rainfall to ours but with an excellent depth of soil to hold moisture.
Fallow
Traditionally the carry-over of winter rains to provide moisture for summer-growing perennials has been enhanced by the cultivated fallow. Vineyards and olive groves have been cultivated in the spring to kill the annuals and reserve all the available moisture for the trees.
It is most important to control summer weeds on a fallow as they have evolved into most effective water scavengers. Whereas most plants can only access, say, half the water in a typical clay soil, the summer weeds can take more. Their effect carries over into the autumn as the first rain only fills the additional deficit created by the summer weeds.
Spring fallow is an effective technique, proven over many centuries, but the benefits of moisture storage are off-set by the high cost of damage to the structure of the soil. The frequent cultivation destroys the organic matter in the soil. It loses its structure and friability. When the rains come in autumn the poorly structured soil forms a cap. The water runs off and rapidly washes away the soil. Some growers cultivate again in the autumn to break the cap but the effect is short-lived and cultivation is the problem not the solution.
Many olive groves in southern Spain with their trees perched on mounds representing the old soil level are witness to the erosion of the surrounding land caused by decades or centuries of fallowing. Fortunately many farmers are becoming aware of the destructive effect of fallow and are today simply mowing the grasses and legumes under their trees or vines. An annual rainfall of 600mm or more provides enough moisture for both the trees and the mown grass. With less rainfall there are benefits in the form of additional yield that need to be carefully weighed against the erosion potential.
For gardeners fallow remains a useful means of reserving soil moisture for perennials to use during summer. Adding organic matter in the form of compost or mulch can negate the destructive effect of constant cultivation. We use newspaper to kill the annual plant competition around our trees instead of cultivation. The newspaper is laid three or four sheets thick around the trees and covered with cut grass to prevent it blowing away in the wind. The weeds, denied light, soon die. Rain or applied water passes through the paper. Next winter the wild boar and porcupines churn up the paper and mulch which decomposes into compost. Even without the depredations of pigs and porcupines the paper rots away in a couple of years and we feel it is more environmentally friendly than using the better-known technique of a mulch of black plastic.
Plant density
The density of perennial plants is critical to their ability to withstand drought. A striking example is the planting distances between olive trees in Tunisia. As one moves further south into more arid regions farmers have increased the distance between each tree to allow the roots to exploit a greater volume of soil. It is a lesson that foresters on the Green Dam project in Algeria failed to understand. They planted huge numbers of drought-resistant trees over thousands of kilometres across the edge of the Sahara and found that many trees died after four or five years – just at the stage when the trees began to compete with each other. They had not realised that even the most drought-resistant trees will not survive a drought when there is intense plant competition.
For the gardener the important lesson to learn is that there is no absolute level of “drought resistance” but an interaction between the ability of the plant to withstand a lack of water and the volume of soil it can command.
Using these principles in reverse, it is possible to take plants from an extremely arid environment and grow them in a better environment at a higher density. Atriplex species are well adapted to desert conditions where the average rainfall is less than 200 mm per year. Even then they are sparse in the natural environment. We have seen Atriplex being used as a hedge in Tunisian gardens at Zaghouan (rainfall about 400 mm) where box would not survive this combination of low rainfall and high density.
Water harvesting
The Nabateans are probably the most famous water harvesters. They collected the runoff from the rocky hillsides surrounding Petra and fed it into their small terraced fields. Crops grew on the moisture provided and stored in the soil. Many Mediterranean Garden readers have written of their experience in storing water from roofs in tanks but few seem to have considered the possibilities of water storage in the soil.
Ironically the problem is managing the excess. Most Mediterranean populations now live in areas with annual rainfall more than 500 mm rather than the 150 mm or so received in southern Jordan. All the north shore of the Mediterranean except for some Greek islands, a small part of Sicily and part of the east coast of Spain have well over 500 mm. All the major cities of North Africa have over 500 mm except Tripoli. Harvesting all the water from roads and other runoff areas in regions with annual rainfall of more than 500 mm and feeding it on to olive groves, vineyard or gardens can lead to waterlogging for most of the winter and early spring if drainage is poor. In those dry winters and springs that are a precursor to real drought this additional water will saturate the soil profile and be a great advantage for the summer. In areas with less than 500 mm of rainfall the benefits of additional moisture are much greater than the hazards of any surplus.
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