Growing lavender in Australia: drainage, humidity and pruning

Lavender is replaced more often than most garden shrubs. It goes in healthy, flowers well through its first spring, thins out over a humid summer, and by the second winter it is a grey skeleton with a tuft of leaf on one side. Very little of that is the plant's fault. Drainage, airflow and one pruning mistake account for nearly all of it, and the site settles two of the three.

The groups, and what each one will tolerate

The lavenders sold here behave differently enough to change your buying decision, so start with the group, not the flower colour.

English lavender, Lavandula angustifolia

The perfumed one, the source of lavender oil, and it tolerates cold better than the others. It is also unforgiving of humidity. It wants cold winters, dry summers and sharp drainage, which describes inland Victoria, the southern tablelands, the Adelaide Hills and the wheatbelt behind Perth far better than any coastal strip north of Sydney. Where it suits, it is long lived. English Summer Blue is the straight angustifolia here.

French lavender, Lavandula dentata

Toothed grey-green foliage, a softer resinous scent, more humidity tolerance than the other common groups, which is why it turns up in Brisbane and northern rivers gardens more than anything else. It is coarser in habit and weaker in perfume, and it is not part of this range at present, so if dentata is what you want, source it locally rather than dropping an angustifolia into a subtropical bed and hoping.

Spanish lavender, Lavandula stoechas and Lavandula pedunculata

These carry the flag-like bracts above the flower head, and pedunculata holds them on long stalks, which is where the butterfly look comes from. They take heat better than angustifolia and flower earlier and harder, but they are shorter lived and resent wet feet just as much. Fairy Wings Spellbound and Fairy Wings Radiance come in 140mm and 180mm, and Blushberry Ruffles sits at the softer pink end. Lavandula stoechas has naturalised in parts of southern Australia, so if you garden near bushland, deadhead rather than letting seed heads dry on the plant.

Garden hybrids

The garden hybrids, Lavinnova among them, sit between the groups, selected for garden performance rather than oil, so you get a longer flowering window and tidier habit at the cost of some perfume. Silver Princess has strongly silver foliage and holds shape well in a pot, and Double Lavish Rose is a 170mm plant with a doubled flower head. The full range sits in the lavender collection.

Drainage comes before everything else

Lavender in Australia rarely dies of drought, cold or neglect. It dies of root rot, in summer, in soil that stayed wet for three days after rain. If you fix nothing else, fix this.

Test the site first. Dig a hole a spade deep, fill it with water, let it drain, then fill it again. If the second fill is still sitting there hours later, that spot will kill lavender whatever you buy. The answer is not compost: heavy soil with organic matter dug through it holds water better, not worse.

Mound instead. Build the bed up two to three hundred millimetres above grade, work coarse sand or fine crushed rock through the soil, and plant into the top so the crown sits proud. Mulch with gravel rather than bark or sugar cane, and keep it back from the stems. Bark held against the base of a lavender is a reliable way to rot the collar.

Pots are a legitimate answer, not a compromise. A 140mm plant runs happily in a 300mm to 400mm pot of free-draining mix, and it lets you control moisture where the ground never would. Do not use a saucer.

Airflow, sun and the summer wet

The second killer is still air. Lavender needs its foliage to dry after rain and dew, and a plant crowded against a paling fence or planted shoulder to shoulder with its neighbours will not manage that. Give each plant its full mature width even though the bed looks sparse in year one. Space is the treatment.

Full sun means at least six hours of direct sun, and morning sun beats afternoon because it dries the plant earlier. Keep lavender off spray irrigation and out of beds watered on the same cycle as lawn or annuals. Drip at the base, and only once the soil has dried. More lavender is lost to a well meaning irrigation controller than to any pest.

Lavender will not reshoot from bare old wood

The base of an established lavender turns into hard, grey, leafless wood, and that wood carries no dormant buds. Cut into it and you get stubs that stay stubs. There is no reshoot the following spring and no renovation prune that brings a bare plant back.

So how far you can reduce a plant is set by where its green growth stops. You can cut back to just above the lowest leafy shoots, and a moderately leggy plant can be brought in over two or three seasons, but cut below the foliage and there is no recovery. One already bare and split open at the base is finished: enjoy it as it is or replace it. Westringia looks like lavender and behaves like it here: neither reshoots reliably from bare old wood, which catches gardeners who assume a grey-leaved shrub can be cut back and started again.

Pruning technique and timing

The first two years

Start earlier than feels necessary. Tip prune after each flush, taking the spent stems plus a little leafy growth, and aim for a low dome rather than an upright bush. Each of those cuts branches the plant lower down, which is your only insurance against the woody base problem. A plant left to flower freely for two seasons without shaping is leggy by year three and unfixable by year four.

Established plants

Prune once the main flowering flush is finished. Follow each stem down and cut just above the lowest healthy green growth on it, never below. You are removing the flower stems plus roughly the top third of leafy growth. Keep a dome rather than a flat top, because a dome lets light reach the lower foliage and that is what keeps the base clothed.

Timing depends on climate more than the calendar. In cold districts, prune in late summer or early autumn so new growth hardens before frost, then leave the plant alone through winter. In warmer areas, prune after the main flush and shear spent heads off through the season. Never prune hard into winter in a frost district, or prune a plant already stressed by heat or waterlogging.

When not to buy lavender at all

In the humid subtropics, from the Sunshine Coast down through Brisbane, the Gold Coast and the northern New South Wales coast, lavender is a short lived plant and no amount of technique changes that. Warm nights and a wet summer are the exact combination root and stem pathogens want. English lavender in particular is often gone within a season or two.

That does not mean do not buy. It means buy with the right expectation: plant in autumn, in pots or a raised bed, treat it as a winter and spring display, and accept you may replace it every year or two. What does not work is putting angustifolia into a subtropical garden bed and expecting a permanent shrub.

Skip lavender entirely if the site is shaded for much of the day, if the bed sits on unimproved clay and you will not mound it, if it shares an irrigation zone with thirsty plants, or if you want a formal clipped hedge that can be cut back hard later. For those situations, westringia gives similar grey foliage with far more tolerance of humidity and hard pruning, African daisy flowers heavily in the same dry, sunny positions, and grevillea handles heat, poor soil and coastal exposure while feeding birds. Our guide to low water gardens in Australia covers the wider palette, and coastal planting for salt and wind is worth reading near the front line.

Buying, planting and feeding

Plants here run from 140mm to 200mm pots. A bigger pot buys little for a plant this quick to establish, and a 140mm plant shaped from the start will usually outperform one left to run. Plant in autumn where winters are mild, or early spring where they are not.

Feed lightly or not at all. Lavender flowers better and lasts longer in soil of modest fertility, and heavy nitrogen produces soft growth that flops, rots and attracts sap suckers. One light application of a balanced slow release fertiliser in spring is plenty. For more colour through the season, plant alongside it from the flowering and low maintenance ranges rather than pushing the lavender harder than it wants to go.

Every order ships farm-direct with flat $99 delivery in QLD, NSW, VIC, SA, ACT and WA, a $399 minimum order, and the 30-Day Healthy Plant Guarantee.