Low water gardens: plants that cope once established - Plant Drop

Low water gardens: plants that cope once established

Every drought tolerant plant list ends with the same three words: once established. That phrase carries the weight, and it is the part people skip. Established does not mean planted. It means the roots have left the hole you dug and pushed out into surrounding soil, deep enough to find moisture you are not supplying. For a 140mm plant that can happen inside a season. For a 100L tree it takes two summers of genuine watering, and if you stop after the first one you will lose stock in the second.

This guide covers those two years, and which plants hold up afterwards. Everything named is in the low maintenance range.

Why new plants die of thirst in wet soil

A plant arrives with its roots in potting mix, which is coarse and free draining and dries much faster than the clay or loam around it. Water the bed lightly and the soil wets while the root ball stays dry. The plant wilts, the owner checks the ground, finds it damp, and looks elsewhere for the cause. Three things prevent this:

  • Water onto the root ball itself for the first two months, not just the bed.
  • Backfill with the soil you dug out, not with potting mix. A pocket of rich mix in clay behaves like a bucket and roots circle inside it.
  • In heavy clay, break up the glazed sides of the hole with a fork before planting. A smooth auger hole holds water like a pot with no drainage.

The two summer watering plan

The aim is deep and infrequent. Frequent light watering builds a shallow root mat in the top 50mm, the layer that cooks in a heatwave. Long soaks, well spaced, force roots down, and that depth carries the plant afterwards.

Stock size Water per plant, per soak First summer Second summer
140mm to 200mm 4 to 8 litres Twice a week Weekly, then fortnightly
45L 20 to 30 litres Twice a week Weekly
100L 40 to 60 litres Twice a week Weekly to fortnightly
200L and above 80 to 100 litres Two to three times a week Weekly

Adjust to your soil. Sand needs smaller volumes more often. Clay needs the full volume applied slowly, or most of it runs off. Rain under about 10mm does not count. Autumn and winter plantings are much easier than spring ones, since the plant gets months of mild weather to root out before it is tested, so schedule advanced trees and 100L and larger stock for the cooler half of the year.

Hydrozoning: stop mixing water needs in one bed

Hydrozoning means grouping plants by how much water they want and running one irrigation zone per group. The usual failure is a bed of dry country natives with two or three thirsty feature plants dropped in for interest. The bed then gets watered at the rate the thirsty plants need, and the natives sit in damp soil all summer. Emu bush and grevillea do not die of drought in that situation. They die of root rot. In practice:

  • Keep the water hungry plants close to the house, on their own line. Everything further out goes on the dry zone.
  • Put the driest zone on the hottest, most exposed aspect, usually the western and northern boundary.
  • Low points and downpipe outfalls collect water whether you plan it or not, so use them for plants that tolerate periodic wet, such as bottlebrush and paperbark.
  • Cap the dry zone once establishment is over. Many low water plants decline slowly under permanent irrigation.

Mulch, and the mulch mistakes

Mulch does as much for water use as plant selection does. Bare soil loses moisture from the top layer continuously and grows the weeds that compete for what is left.

  • Go 75mm to 100mm deep and top up annually. Under 50mm suppresses little and breaks down within a season.
  • Use a coarse, chunky mulch. Fine, dusty mulches mat down and shed light rain off the bed instead of letting it through.
  • Keep mulch off the trunk and root collar. Piled against the stem it holds moisture on bark and invites collar rot.
  • Pebble and gravel mulch conserves water but radiates heat. It suits arid natives and punishes anything soft leafed.

What actually copes here

Screening and hedging

Westringia is the workhorse of the dry hedge. It handles coastal wind, salt and poor soil, and it clips into a formal shape. It does need pruning to stay dense, since an unpruned plant opens up and goes woody at the base. Trim lightly and often rather than cutting into old wood.

Indian hawthorn gives a low, dense hedge on far less water than the usual lilly pilly. Eremophila, the emu bush, comes from arid inland country and is genuinely dry adapted, but it wants sharp drainage and open air. It struggles in humid coastal summers on heavy clay, and it dislikes being overwatered once it is in. Plant it high, on a mound if your soil is heavy, and leave it alone.

Trees

Olive is a strong choice for a hot, exposed site and it clips well as a hedge or a standard. Two cautions: fruit drop stains paving and gets walked inside, so fruiting forms belong away from entries and driveways, and olives are treated as an environmental weed in parts of southern Australia, so check with your council before a large planting.

Gum trees and kurrajong handle dry conditions once away, though large trees still need siting clear of buildings, paving and services. Wattle establishes quickly and asks for very little, though most species are short lived next to a eucalypt, so use it as the fast filler while slower trees size up, not as the permanent structure.

Ground layer and mass planting

This is where a dry garden is won. Mat rush, Lomandra, is the default mass planting for hot Australian sites: sun or part shade, poor soil tolerant, and it holds its form without shearing. Flax lily, Dianella, does the same job in a finer texture and takes more shade. Both look tired after a long dry spell, and both respond to a hard cut back in late winter rather than to more water.

Kangaroo paw adds flower without adding irrigation, given drainage and sun. Lavender wants a Mediterranean climate and free draining soil, and it sulks in humid subtropical summers, so it is a southern states plant more than a Queensland one. African daisy covers ground fast but goes woody in a few years, so treat it as a filler you plan to replace.

For the sculptural, succulent style silhouette, New Zealand flax and the hardy green leaved forms of cordyline fill that role. The tropical coloured cordylines have different needs and are not dry garden material.

Spacing

Planting Role Centres
Flax lily Mass groundcover 400 to 600mm
Mat rush Mass groundcover 600 to 800mm
Westringia Clipped low hedge 500 to 600mm
Indian hawthorn Low hedge 600 to 800mm
Emu bush Open shrub layer 1 to 1.5m
Olive Clipped screen 2 to 3m
Olive Avenue or feature 5 to 7m

Cultivars vary a lot in mature width, so check the spread on the line you are buying. Resist tightening the spacing to fill the bed faster: crowded dry plantings compete for the same soil moisture and thin out from the base.

What to keep out of a dry bed

Being clear about this saves real money. Maples, and Japanese maple in particular, want cool root runs, shelter from hot wind and steady moisture, and they scorch on an exposed western boundary. Camellias and magnolias are worth growing, but not in a dry zone. Silver birch gets planted in full sun on the strength of its looks and then struggles through its first hot summer. Coral bells want shade and moisture. None of these are bad plants. They belong in the irrigated zone near the house, which is what hydrozoning is for.

Ordering

Plant Drop supplies farm direct to QLD, NSW, VIC, SA, ACT and WA on flat $99 delivery, with a $399 minimum order. Tasmania and the Northern Territory are outside the delivery area. Put the budget into structure, the trees and the screen line, and buy the ground layer as smaller stock in quantity, since mat rush and flax lily catch up fast. Start with the low maintenance collection.

Plants featured in this guide

Everything below is currently available farm-direct, with flat $99 delivery in QLD, NSW, VIC, SA, ACT and WA and a $399 minimum order.

Browse the full range: Low Maintenance Plants · Mat Rush · Flax Lily · Grevillea

Related ranges: Lavender, Agapanthus, Succulents, Liriope and mondo grass.

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