Japanese maples in Australian gardens: getting the position right - Plant Drop

Japanese maples in Australian gardens: getting the position right

Japanese maple (Acer palmatum) is a tree we send out a lot, and one that is regularly killed in its first two summers. It is not a difficult plant. The problem is that it gets chosen from a photograph rather than from a reading of the site, and then planted where an Australian summer takes it apart.

Why Japanese maples scorch

The leaves are thin, finely divided and hold almost no water reserve. The roots are shallow and fibrous, sitting in the soil layer that dries out first. On a hot, dry, windy day the leaf loses water faster than those roots can replace it, and the margin dies back from the tips of the lobes inward. That is scorch. It is not a fungus and no spray fixes it.

Three things drive it, usually together:

  • Direct afternoon sun in summer. Morning sun is mild and the air still humid. Midday sun in January arrives with dry air and high leaf temperature.
  • Dry wind. A hot northerly will burn a maple that would have coped with the same temperature in still air. Wind matters more than the number on the thermometer.
  • Reflected and stored heat. Pavers, concrete, render and steel fences re-radiate heat into the canopy for hours after the sun moves off. It is why sheltered-looking courtyards are where maples so often die.

Scorched leaves do not recover; the tree holds them, looking burnt, until leaf fall. One bad episode is survivable. Scorching every summer is what kills the tree, because it never builds the reserve for a strong spring flush.

Getting the position right

The target is simple: direct sun in the morning, shade or dappled light from late morning onwards, and shelter from dry wind.

Position What actually happens
Sun until mid morning, shaded after The position they want. Full leaf through summer, strong autumn colour.
Dappled light under a high, open canopy Works well, unless the overhead tree is a heavy surface feeder competing for water.
East side of a house or fence Reliable in most temperate districts. The building does the work.
Full sun, open and exposed Scorches in the first hot, windy spell. Survivable only in cool districts with irrigation.
West-facing wall, afternoon sun The hardest position in the garden. Late sun plus stored wall heat. Avoid it.
Dense shade all day Survives but sulks. Thin drawn growth, red forms fade to muddy green.

Leaf colour changes the tolerance. Plain green forms take the most sun. Red and purple forms need some direct morning light or they go green by midsummer. Variegated forms are the touchiest and should be treated as shade plants in anything warmer than a hills district. When you are choosing from the Japanese maple range, let the position you actually have decide the leaf colour, not the other way around.

Dissectum or upright: two different plants for two different jobs

Upright palmatum forms

These build a vase-shaped to rounded small tree with a trunk and branch structure that carries the garden through winter. Use them as a specimen near an entry or as a focal point at the end of a sight line. They lift their canopy over time, so you can underplant them. Buy one with a decent leader and clean branch spacing: the framework you buy is largely the one you keep. The semi-advanced grades give a usable shape years earlier than a small pot.

Dissectum, the cut-leaf and weeping forms

Dissectums mound rather than climb. They are wider than tall and they cascade, which makes them the choice for the top of a retaining wall, beside water, over a step, or in a large pot. Two points people miss. First, the finely divided leaf has more edge exposed for its volume, so it scorches sooner than an upright form in the same spot: give a dissectum more protection, not the same. Second, weeping forms are usually grafted at height onto a standard, and that graft height sets the final height. The plant spreads and thickens but will not grow taller, so buy the height you want.

Pots and courtyards

Maples do well in pots, and dissectums are the better pot subject. The failures are usually about heat at the roots, not light on the leaves.

  • Go bigger on the pot than looks necessary: volume buffers root temperature and moisture, and a small pot in February cooks.
  • Avoid thin black plastic and unglazed terracotta in sun. A thick-walled or glazed pot in a light colour holds a steadier root temperature.
  • Use a free-draining mix, raise the pot on feet, and site it so the pot itself is shaded, even if the canopy catches morning light. Shading the container matters more than shading the leaves.
  • Root prune and refresh the mix every few years, or the plant declines slowly whatever you do.

Districts where they genuinely suit

They are reliable in cool and elevated temperate districts: the Adelaide Hills, the Blue Mountains, the Southern Highlands and Central Tablelands, the Dandenongs and Yarra Valley, most of suburban Melbourne and Geelong with some shelter, and Canberra, where they need wind protection and some allowance for late frost on new spring growth. Colour is strongest where autumn nights get cold, which is why the same cultivar performs differently in Bowral and in Botany.

They are marginal on the Sydney coastal fringe, the Adelaide plains, the Perth coastal plain, and across inland NSW, Victoria and South Australia. In those districts they are a sheltered courtyard or protected east-side plant with reliable irrigation, not a lawn specimen.

They are not the right tree for Brisbane, the Sunshine Coast, the Gold Coast or further north. Heat plus humidity is hard on them, and without cool autumn nights the colour people buy them for does not arrive. In the subtropics, choose from the feature trees or the tropical range instead.

When to plant a trident maple instead

Trident maple (Acer buergerianum) is the tree to reach for when you want maple character in a position Acer palmatum cannot hold. It takes full sun, heat, wind and compacted soil, it colours in autumn in warmer districts, and it stays at a size a suburban block can carry. Both sit in the wider maple range.

Situation Choose
Sheltered east side, courtyard or dappled shade, cool district Japanese maple
Driveway, nature strip or open lawn, full sun and wind Trident maple, from the maples
Hot open position, low water, summer flower wanted Crepe myrtle
Formal avenue on an exposed site Ornamental pear

Planting, and the first two summers

Plant in autumn or winter while the tree is dormant, so the roots move out before the first hot weather. The soil has to drain: a hole dug into heavy clay behaves like a bathtub, so on clay plant into a raised or mounded bed. Mulch wide and deep, kept clear of the trunk. Wide matters more than deep, because you are insulating shallow surface roots across the whole root zone. Do not cultivate or dig under an established maple.

Water deeply and less often, at the root zone, and check the soil rather than watering to a schedule. Skip high-nitrogen fertiliser, since soft fast growth scorches worse than steady growth. Keep pruning light and limited to dead or crossing wood, and prune in late autumn or early winter: cuts made at the end of winter bleed sap heavily. If your tree is grafted, rub off any shoots below the graft union as soon as they appear, or the rootstock takes over.

A smaller tree in the right position will overtake a large tree in the wrong one. If the budget forces a choice between a bigger grade and fixing aspect, shelter and soil, fix the site.

What to plant with them

The position a maple wants is sheltered and part shaded, so the companions choose themselves. Camellias give evergreen structure and winter flower in the same light, coral bells work as foliage at the base, and flax lily and mat rush hold the soil without competing hard for water. Avoid running lawn to the trunk: keeping turf green means watering in a pattern that does not suit the tree.

For a larger job, price the advanced tree grades against the smaller stock. Delivery is a flat $99 per order on a $399 minimum, so consolidating a planting into one order is usually the sensible way to buy.

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: Japanese Maples · Maples

See also: Cercis and Forest Pansy, Liquidambar.

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