Waterwise and Waterless Gardens

Merv Hodge

I regard a waterwise garden as the effective minimal use of supplementary watering and a waterless garden as one that relies wholly or mainly on natural rainfall, except for initial watering to get the plant started. My garden falls into the latter category.

Whether you believe in climate change or not, you must admit that much of Australia is currently subjected to a long, hot, dry period and most of the capital cities are experiencing a water shortage. Brisbane, at least, has severe water restrictions and residents are shortly to only be allowed to water their gardens by bucket. This is exacerbated by a reported migration into Queensland from southern states in the order of more than a thousand persons per week. Most of these appear to be settling in south east Queensland, particularly in and near Brisbane and they are causing an extra drain on our meager water supply.

The best strategy is to use plants that are drought- tolerant and adaptable to the local environment. Native plants are a good suggestion for this purpose, but being mindful of the fact that some natives like plenty of water, we should be cautious about which natives we promote. I remember some bad advice given some years ago, "Grow natives for a no-maintenance garden".

Grevilleas could be considered for the waterwise garden, but each person should select the best suited to their particular conditions. There is the added bonus of attracting birds to the garden.

There are a number of strategies that can be consider to help make the most of the water supply or the natural rainfall. Considering that we have the double whammy of water restrictions and hotter climate in our part of the world we should concentrate on northern grevilleas. Generally in south-east Quensland it is easier to bring plants from north to south than from south to north.

I find that the best time to plant in our part of the world is mid-autumn to mid-winter. There is less stress on the plant and it has a better chance of establishing its root system before summer. August/September are normally the driest months and dry westerly winds further exacerbate the situation, especially during August.

In sandy or very well-drained soils I would prefer to plant in a slight depression to collect water around the plant. Conventional wisdom is to normally plant on a slight mound so that water doesn't collect around the trunk and cause collar rot. A rule of thumb to check drainage is to dig a hole big enough to accommodate the root-ball of the new plant and pour in a bucket of water. It should disappear fully within five minutes.

When planting, give the plant a thorough watering after backfilling so as to ensure good contact between the backfill and the rootball. Follow-up watering, decreasing the frequency over 6 to 8 weeks, depending on rainfall and soil type. The most any grevillea should need after establishment is no more than once per week.

After establishment connect drippers if these are allowed by the local authority. The drippers are best controlled by a timer so that over-watering is prevented. Two or three drippers are best for each plant to give even watering around the plant.

Planting on a slope

If planting on a slope, dig a shallow channel on the top side of the plant to catch water and assist it to penetrate the soil near the plant. It can be shaped like a boomerang so that water is directed towards the plant.

Mulches

Use organic mulches to no more than 5-1 Ocm (2-4 inches) deep. It can be a wasted expense if too deep and it will probably prevent light rain from being effective. Mulches tend to maintain even temperature and even moisture as well as suppressing weed growth. Do not pack mulch up against the trunk of the plant because this could cause collar rot. Keep a gap of about 20mm between the trunk and the mulch. Organic mulches will burn so you may wish to weigh up the risks and benefits if bush fires are a possible problem. Organic mulches include shredded sugarcane, tea tree mulch, lucerne, forest litter (shredded trees). Gravel is sometimes used but weed seeds readily fall into it and germinate. A blower may be needed to keep it clean but it is fireproof.

Weedmat, Plastic and Newspaper

Do not use weedmat or plastic under mulch -they both assist compaction, cut off air exchange to the soil and exist there forever. Generally water will be shed off them rather than get through to the plants. They are also a nuisance when trying to dig holes for plants. Newspapers should also be avoided under mulch. Water does not penetrate easily and the thicker they are the worse the problem. Newspaper may take years to break down under mulch.

Water Crystals and Hydrocell

Water crystals may be OK but once they absorb water they do not readily release it. The roots of the plant need to penetrate the crystals for the best benefit. These should be placed under the plant when planting. They will eventually break down. When the crystals absorb water they swell up to hundreds of times their own volume. One teaspoon under a plant is generally sufficient. It is a good idea to soak them and allow them to swell before placing them in the hole. Follow the directions on the container or you may be surprised to see plants popping up out of the ground.

Hydrocell is another product that stores water. It looks like chunks of polystyrene, but when wet it feels like wet cottonwool. This does not significantly swell when wet. It readily releases water into the soil around it when the soil becomes drier. Both of these products only store water they do not make it, so eventually even they can dry out.

I stored a similar amount of each in identical open Chinese food containers and noted that after about one week the Hydrocell had dried out but the water crystals looked as if they had not lost any water. This tends to agree with their ability to release water into the soil. I intend to repeat this, weighing each before and after to check water loss.

Soil Wetting Agents

Soil wetting products are useful in allowing dry soil to more readily absorb water rather than repel it. This can particularly happen with sandy soils with little organic matter incorporated. Three products are 'Wettasoil', 'Moistur Aid' and 'Penetrade'. They need to be re-applied every six months.

Antitranspirants

Antitranspirants can be useful to cut down the moisture loss of the plants. They will need to be reapplied periodically, depending on rainfall. They are also useful for frost and heat protection. Three product names are 'Envy', 'Stressguard' and 'Floraguard'.

Grow Tubes

Grow-tubes are cylindrical objects open top and bottom, standing vertically surrounding the plant to create a microclimate and give protection against wind, frosts and small animals. The tube should be at least as tall or taller than the plant it is to protect. Three or four small stakes should be placed around the plant to support the grow tube. These can be fashioned from recycled shopping bags (or other plastic bags) cutting open the bottom and care taken to anchor the bag down to stop it blowing away. I have also seen cardboard milk containers used. They were cut down one side and the bottom removed and two or three stapled together to form cylinders, depending on the size of the plant to be protected. There are also manufactured grow-tubes in a long roll so that a length required to protect the plant can be cut off the roll.

A combination of all or most of the above will give your plant the greatest chance of survival but any one on its own will help.

It is essential that you read all directions and precautions on the containers when using any of the products in this article.

From the newsletter of ASGAP's Grevillea Study Group, June 2006.

Australian Plants online - 2006
Association of Societies for Growing Australian Plants