By Kate Wall
Where ever you live in Australia, periods of extended dry weather and even drought are likely to impact on your garden. Water restrictions are likely to remain as long term realities which will limit the amount of supplementary watering you are able to give your garden during these dry times.
A garden which requires less watering during dry times will have a distinct advantage and will look better for longer during extended periods of drought. Reducing the need for supplementary watering can be done in a few different ways, including garden management practices and selection of drought tolerant plants.
Garden management practices which reduce the need for supplementary watering include mulching, soil improvement, reduced fertilising, and timing of fertilising and pruning in addition to planting and watering techniques.
Soil improvement is critical for all garden success but in times of drought is even more so. A soil which has had organic matter added is better able to hold moisture in addition to having a better structure allowing better access for plant roots to penetrate deeply into the soil. Organic matter acts like a sponge in the soil, holding moisture for significantly longer. Organic matter is best added as aged compost and can be placed on top of the soil if it is then covered by mulch, otherwise should be dug in. The added organic compost also provides slow release plant nutrients which is essential during drought.
Water crystals can be added to sandy or very dry soils to aid water retention. Water crystals work best when they are soaked before digging into the soil, as they will swell significantly and if placed dry into the bottom of a planting hole, can swell enough to push the new plant out of the ground. Water crystals should not be placed on the surface but dug into the soil so plant roots will find them. An organic alternative to water crystals is to add vermiculite to the soil. Vermiculite has the advantage of also being able to increase the porosity of the soil, holding air and nutrients as well as water. If water crystals or vermiculite can added to the bottom of a planting hole, or a little deeper, they will help enormously to sustain new plantings through dry periods. By soaking the water crystals or vermiculite in a weak seaweed solution before adding them, you will be providing valuable nutrition to aid with plant stress, reducing transplant shock and improving drought tolerance.
Mulch is important for providing soil protection. It is able to protect soils from erosion and from temperature extremes in addition to conserving water in the soil. Mulch can also aid in weed suppression and make a garden look fresh and tidy so is valuable in any garden. The type of mulch used is often an aesthetic decision, however not all mulches will provide the same value. Fine mulches should always be avoided. They tend to form compacted crusts which prevent water penetration. When these fine mulches are used, water more often simply runs off the top and does not reach the garden at all, making the garden below even drier than if the mulch were not used. By using an uneven or chunky mulch it is not able to form a tight compacted crust, and will always have air spaces in the mulch which allows water to easily trickle through to the garden below.
Mulch should be applied thickly enough to give good protection but as water has to penetrate through the mulch to reach the ground, if the mulch is too thick it is much harder to get sufficient water to get through. 3 – 5 cm is usually thick enough for most gardens. As the mulch breaks down it will need to be replenished. For most chunky mulches this will usually be an annual job. It is a good idea to apply fresh mulch in spring to prepare the garden for the heat of summer. This is a good time to apply a slow release fertiliser under the mulch and give the garden a deep watering before adding the mulch.
Slow release fertilisers are usually best for the garden but during drought are particularly important. Water stressed plants are not able to take up fertiliser, so fast acting fertilisers can be wasted, or can burn stressed plants. Never fertilise plants at all during extreme drought.
Slow release fertilisers can remain in the soil for long periods and the plants are able to take up small amounts as they receive sufficient water to do so. Regular applications of a seaweed solution can assist plants to cope with stress, including drought. This should be applied as a foliar spray and applied during cool periods of the day when there are no strong winds about.
Avoid major pruning tasks during dry weather in most cases, as the plants do not have the available water to re-shoot vigorously. In extreme cases you may notice trees and shrubs dropping leaves. This is a drought protection mechanism as with less leaves the tree loses less water through transpiration. Careful pruning of small trees can remove excess leaves and emulate this natural process. If pruning must be done, always follow up with a deep watering to reduce plant stress.
Watering techniques are critical to drought management of gardens. Always water in the cool of the evening when evaporation is reduced, unless your night time temperatures are likely to be below 15OC, in which case you will be better to water in the cool of the morning. Watering is always more effective if it reaches deep in the soil to the plants root zone. Frequent shallow watering can actually cause plants increased drought stress and even plant deaths. Plants need to be encouraged to have deep roots for increased drought tolerance. A deep soak once every week or two will be far more beneficial for your garden then regular short waterings. To check if your watering has reached the root zone of your plants, dig a small hole and see how far the water has penetrated into the soil. This is usually best done with a watering system or sprinkler but you will need to ensure this complies with local water restrictions.
Whilst all of this additional garden care will help get most gardens through periods of extended dry weather, by planting drought tolerant plants you are able to significantly increase the drought tolerance of your garden. You can find out more about drought tolerant plant selection here.