How to grow Custard Apple in Australia

Where to plant

Custard apples need a warm, frost-free, well-protected spot in full sun. Frost can kill or severely damage both young and bearing trees. The wood is soft and brittle and the branches break easily in wind, especially when carrying a full crop, and wind rubbing marks the fruit skin, so shelter matters as much as warmth.

Queensland DPI advice is that the trees need at least 1 m of well-drained soil without heavy clay or rock to avoid root rot; where the topsoil is shallower, plant on a mound. Sandy loams suit them best. Avoid ground where tomatoes, potatoes, eggplant, capsicum or ginger grew recently, as these can carry bacterial wilt, which also attacks custard apples.

The tree is fussy about flowering weather. Fruit sets best at about 25 to 28°C with humid air during flowering, from October to February. Hotter weather gives more leaf and fewer flowers, and Queensland DPI says custard apples are not suited to the hot coastal tropics or hot inland areas.

• South East Queensland and the Northern Rivers: the heart of Australian custard apple growing. Plant from September to February in a sheltered, frost-free spot.
• Sydney: marginal. Plant from October to January in the warmest, most sheltered north-facing spot near the coast. African Pride is the variety that crops furthest south, and frost in the west kills young trees.
• North Queensland: plant from September to February, but the atemoya custard apple sets fruit poorly in hot coastal lowlands, so it does best on the Atherton Tableland. Darwin: not suited, as Queensland DPI says custard apples are not suited to the hot coastal tropics. In the hot tropics, its parent the sugar apple is the more reliable choice.
• Melbourne, Adelaide, Perth, Canberra and Hobart: not suited, as the season is too short and too cold.

Choosing a variety

Buy a grafted tree. Seedlings are slow to fruit and variable.

How to plant

1. Plant in spring or summer when the soil is warm, so the tree settles before winter.
2. Choose a sheltered, sunny spot with deep, well-drained soil, or build a wide mound if the soil is shallow or heavy.
3. Water the tree in its pot well, then plant it at the same depth it sat in the pot, with the graft union above the soil.
4. Water in deeply and mulch widely, keeping the mulch clear of the trunk.
5. Allow about 6 m between trees, or less if you will prune hard to keep them small.

Watering and feeding

Keep the soil evenly moist from flowering through fruit set and while the fruit grows. Even moisture gives bigger crops and stops the fruit splitting. Ease off watering in winter when the tree is semi-dormant, and never let the roots sit in wet soil. Custard apples are sensitive to salty water.

Custard apples do not need heavy feeding. Gardening Australia suggests compost and small, occasional applications of chicken manure, which keeps the soil healthy without pushing soft, brittle growth.

Pruning and pollination

Prune regularly to keep the tree low, open and strong. Gardening Australia describes three prunes a year: a main prune in autumn after harvest to control height, a spring prune to lift the lowest branches off the ground, and a summer tidy to remove water shoots and keep the centre open. A low, open tree is easier to pollinate, net and pick, and less likely to snap under a heavy crop.

Custard apple flowers are first female and then male, so they rarely pollinate themselves, and natural fruit set is poor in most varieties except African Pride and KJ Pinks. Hand pollination makes a big difference.

1. In mid to late afternoon, pick a few flowers whose petals are nearly fully open and whose pollen sacs have turned creamy grey.
2. Leave them on a sheet of paper or a tray overnight at room temperature. The pollen sacs shed onto the paper.
3. Before 11 am the next morning, use a small, soft paintbrush to dab the pollen onto the centre of flowers that are just starting to open, when the female parts are receptive.
4. Use the pollen within 2 to 3 days, as it does not keep.

Harvesting

Fruit ripens over a long season, from about February to early November, with the peak in May and June. Pick when the skin colour lightens, the knobbly segments smooth out and the fruit shows faint stretch marks between them. Clip it with a short stalk, as the soft fruit bruises easily.

Picked fruit ripens on the bench at room temperature over several days and is ready when it gives to gentle pressure. Do not put unripe fruit in the fridge: below about 8°C it suffers chill injury. Once soft, eat it within a day or two.

Using it

Cut a ripe custard apple in half and scoop out the flesh with a spoon, spitting out the black seeds. The flesh is good chilled, in smoothies, fruit salads and ice cream.