Drought-tolerant gardens
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I have written previously on the topic of water efficiency
and how to plan a garden to minimise the water requirements of the plants.
However, when drought conditions prevail the garden often has to be left to
take care of itself entirely, as there are more pressing needs for water.
Planning is the key and the gardens that can best cope with drought are those
using plants that can survive on natural rainfall alone.
Planning for drought is an area that gardeners often ignore. Often that's understandable, droughts don't happen everywhere. However, even without the added pressure of drought conditions we should all consider how best to use our water resources as our expanding cities and the increased prevalence of pollution increase the strain on the availability and quality of water.
Planting for drought doesn't mean that you are restricted to using only dune grasses, cacti and succulents. A drought resistant garden can be just as colourful and enjoyable as any other while also being ready to withstand the worst that summer can throw at it.
There's also the added advantage that a garden better suited to its environment requires less maintenance. Less watering means less labour and plants that aren't going to be damaged by the climate won't require remedial care.
The main points in making your garden water efficient are:
* Irrigating as efficiently as possible.
* Conserving soil moisture by making your soil more moisture retentive and by using mulches to lessen surface evaporation.
* Weeding regularly, as there is no point in allowing water use by plants that you don't want.
* Minimising water-hungry lawns by reducing them to just the area that is actually used.
* Selecting drought-tolerant plants or those that are not active in the dry season and grouping your plants according to their water requirements.
Those requirements apply equally as much to drought-tolerant gardens as to those designed merely to minimise water use. There is an additional requirement too: shelter from drying winds. Good wind protection goes a long way towards minimising moisture loss from both the soil and the plants' foliage and also makes for a more pleasant living and gardening environment.
The shade from shelter belts and carefully sited trees
creates microclimates that are suitable for less drought tolerant shrubs and
perennials that would suffer if planted in full sun. Use small-leafed trees,
such as the vanilla tree (Azara
microphylla) or the mayten (Maytenus
boaria), that won't suck up too much of your precious soil moisture to keep
their foliage turgid.
Although our ultimate objective is to eliminate the need for
regular watering, we still need to provide for irrigation, if only to get the
young plants established. In small areas this need be no more than being able
to reach the young plants with the occasional bucket of water. In larger areas
a drip line or soak/seepage hoses are more practical. As a
rule plant smaller rather than larger specimens; young plants have a
much better chance of establishing a wide-spreading root system when
transplanted into harsh conditions.
Anything that can be done to maintain moisture in the soil
has to be beneficial and increasing the humus content of the soil is the best
way to achieve the ideal combination of good moisture retention and good
drainage. And good drainage is important even in dry gardens; plants that
tolerate dry conditions generally won't tolerate poor drainage in wet periods.
Composting your garden waste is not only economical and environmentally sensible, it adds humus and recycles the moisture content of
the composted material.
Mulching conserves soil moisture by reducing evaporation and
it helps suppress the growth and ease the removal of weeds that compete with
desirable plants. Where mulching materials are hard to find, frequent hoeing is
one of the best methods of keeping the weeds down and also creates a fine
surface dust that acts as a mulch.
Lawns are extremely moisture hungry and unless absolutely
essential may be better done without. At the very least reduce the are of lawn
to that actually used and choose a grass like red fescue that can withstand
drought or recover after drying off.
By grouping your plants according to their water use, you
ensure that they all need watering at about the same time. This is far more
efficient than having to irrigate a whole garden when just a few of the plants
need water.
Those are the obvious planning and maintenance considerations, now what about the plants? Well, before considering examples it would pay to look at what makes a plant able to withstand drought. There are five main strategies that a plant can use to withstand prolonged dry conditions.
* The plant can develop a large rhizome, taproot or a network of deep roots that can either store moisture from damp periods or seek out moisture at great depths.
* The leaf surface can be reduced or modified to lessen evapotranspiration. Leaves covered in fine silvery hairs or coated with a waxy cuticle are common among dry-country plants, especially those from coastal regions.
* The leaves can be eliminated altogether and the chlorophyll in the stems used for photosynthesis instead. This is the strategy of leafless shrubs such as broom and is the one adopted by those most famous of drought-tolerant plants, the cacti.
*The plant can become dormant during dry periods and rely on storage organs such as bulbs or tubers to see it through to the next rain. This is commonly seen in South African bulbs such as Nerine and Amaryllis, which are inactive in summer but burst into flower with the arrival of autumn moisture.
* The plant can die, but not before setting seed that will germinate when moisture returns. This is the strategy that makes deserts bloom after rain. Ephemeral annuals grow, flower and set seed in a brief period of moisture.
By capitalising on all of these drought-withstanding strategies you can ensure variety in your garden while also virtually eliminating the need to water after the initial establishment period.
Plants from dry coastal regions, such as the Marlborough Rock Daisy (Pachystegia insignis), often have leaves with wax coated upper surfaces and felting on the undersides. These coating provide protection from salt spray and moisture loss. Other coastal or dry-country plants, such as Artemisia arborescens, Convolvulus cneorum, Stachys byzantina and Euryops pectinatus, have silver leaves to reflect harsh sunlight. They are often drought tolerant and can be used to create very striking effects.
Many grasses have low moisture requirements and they can be remarkably cold hardy too, making them an important part of the dry, inland landscape.
It's possible to create a marvellously colourful, very low-maintenance garden using daisies alone. Shrubby marguerites (Argyranthemum frutescens cvs.) combined with Arctotis, Brachyglottis, Gazania, Euryops possibly with the addition of a few brilliantly coloured ice plants ensures a brilliant display throughout the year, especially in coastal areas.
Using a wide range of plants of the protea family, particularly those from South Africa and Australia such as Leucadendron, Leucospermum, Protea, Mimetes, Serruria, Grevillea, Dryandra and Banksia, also provides year-round flower. Also, their shrubby or tree-like growth habits lend more an air of permanence to the garden than do the rather temporary daisies.
Australian plants in general tend to be drought tolerant. Well-known and widely grown genera like Acacia, Callistemon, Eucalyptus and Melaleuca all include species that can tolerate extreme drought.
Mediterranean plants such as Cistus, lavenders (Lavandula) and oleanders (Nerium oleander) all thrive in hot, dry conditions. They combine well with many other groups of plants and require very little maintenance. Olives are very epitome of a Mediterranean plant and combine drought tolerance with good shading ability and great beauty. Strangely though, I've always felt that an olive tree looks its best when drooping under the weight of a good rain.
In many areas winter tends to be the wettest season, few of us have a Mediterranean climate, which is dry in winter. Many plants that are less drought tolerant can utilise that winter moisture and will give you a winter and early spring show. Pansies, polyanthus, Primula malacoides, Primula obconica, wallflowers, Iceland poppies and Nemesia will all flower in winter and it doesn't matter that they don't last when the summer heat and drought sets in.
Of course, the ultimate dry-country garden style is the one that makes extensive use of cacti and succulents. Such a garden will require little or no irrigation once established and rain may, at times, even be a disadvantage. Aloe, Crassula, Agave, Kleinia, Sedum and the myriad of cacti species have very bold forms that make for distinctive landscaping even when just planted in a haphazard manner and left to fend for themselves.
Tough drought-tolerant palms such as Washingtonia, Brahea armata, Butia capitata and Jubaea chilensis combine well with succulents and cacti, as do the beautifully flowered yuccas from western North America.
Successful gardening through drought comes down to understanding the effects of your cultivation techniques and having an appropriate selection of plant. It's all about planning and working with the natural conditions rather than trying to beat them into submission — common sense really. Done well, the result is a functional and attractive garden that can survive the worst of conditions while requiring very little maintenance other than weeding.
Copyright Geoff Bryant
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