How to Grow Alliums in Australia

Drumstick allium (Allium sphaerocephalon), an ornamental onion in the family Amaryllidaceae, is grown for its flowers, not to eat. Its egg-shaped heads open green, then turn deep purple on stems 60 to 90 cm tall, drawing bees in late spring and early summer. It needs little water once established and fails mainly when wet soil rots the bulbs; garlic, onion and leek have their own guides.

Three mistakes that matter

1. Planting in soil that stays wet. The small bulbs rot in heavy, waterlogged ground and in beds watered through summer. Plant in free-draining soil, a raised bed or a pot, and stop watering once the leaves wither.
2. Cutting the leaves while they are green. The leaves feed the bulb for next year, so removing them early weakens the bulb and gives fewer flowers. Let them yellow and dry before tidying them away.
3. Planting where onions or garlic grew. Ornamental alliums can catch the same diseases as edible ones, and white rot can survive in soil for up to 20 years. Choose a bed with no recent onion, garlic or leek crop.

When to plant

Plant the bulbs in autumn, from April, once the heat of summer has left the soil. Anzac Day sits in the middle of the window, and planting just before autumn rain settles the bulbs in. Flowers follow from November into January, a little earlier in the subtropics, and the bulbs then rest through summer.

Bulbs that arrive early can wait somewhere cool, dry and airy until the soil cools. In the subtropics, a short spell in the fridge crisper before planting can improve flowering; plant straight from the fridge.

Site, soil and setup

Weed status, state by state

Drumstick allium is not known to be naturalised in Australia. In Victoria it has been recorded only as a casual escape, such as at Warrnambool, and was not seen spreading. No state or territory declares it.

It still spreads by seed, offsets and tiny bulbils in the flower head. Snap off spent heads near bushland, and check your council's weed list. Do not confuse it with three-cornered garlic (Allium triquetrum), a declared weed in Victoria and South Australia. That weed has white, drooping, bell-shaped flowers with a green stripe, on three-sided stems.

Container growing

Most alliums do well in deep pots, a good answer to heavy or damp soil. Use a pot with drainage holes at least 30 cm wide and 30 cm deep (about 15 L) for one pack of seven bulbs. Fill it with free-draining potting mix with a little coarse sand or grit added.

• Watering. Pots need more water than beds; keep the mix lightly moist while the leaves grow, but never soggy.
• Feeding. Water in seaweed solution at 30 mL per 9 L every fortnight from the first shoots. Once the first flowers open, switch to liquid potash at the label rate every fortnight.
• Position. Full sun while in growth. Once the leaves die down, move the pot somewhere dry until autumn, or stand it behind other pots to hide the fading leaves.

Planting Bulbs

Drumstick alliums start from dormant bulbs about the size of a large coin, planted pointed end up.

Planting a bed of bulbs

1. Prepare the bed as under Site, soil and setup.
2. Set each bulb pointed end up, 8 to 10 cm deep.
3. Space bulbs 10 to 15 cm apart.
4. Plant in groups of seven or more, because the thin stems look best massed together.
5. Water in well, and keep the soil just moist for the next two weeks to start the roots.
6. Mark the spot, so a spade does not find the bulbs before the shoots appear.

After flowering: leave, lift or divide

Once flowering ends and the leaves have yellowed, let the bulbs rest dry through summer (see Three mistakes). Clumps grow by offsets, and in well-drained soil the bulbs return and naturalise. Lift and divide crowded clumps after the leaves and flowers have died down.

Care by growth stage

Moisture while the leaves are green and a dry summer rest decide how well drumstick alliums flower. They need little feeding: a light start at planting, then potassium as the flowers open.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in as the shoots appear can help.

Companion planting

Plants with spreading leaves or grey foliage hide allium leaves as they die back, and the purple heads rise through them.

Grows well with

• Catmint, a low, sun-loving mound that covers the fading allium leaves.
• Lamb's ear, grey foliage that sets off the purple heads and likes the same dry soil.
• Lavender, which shares the need for full sun and sharp drainage.
• Yarrow and ornamental grasses, feathery plants the stems can weave through.

Keep apart

• Onions, garlic, leeks and chives, which share white rot, downy mildew and onion thrips.
• Thirsty annuals watered through summer, because summer irrigation rots resting bulbs.

Harvesting Blooms

Cut stems for the vase when about half the florets in a head have opened and the stem just below the head feels firm.

• Water the bed the day before, and cut in the cool of early morning or evening.
• Use clean secateurs and stand the stems in clean water straight away.
• Cut the flower stem low and leave the leaves on the plant.
• Strip anything that would sit below the waterline, where it rots and shortens vase life.
• Expect a mild onion smell from cut stems.
• Leave some heads standing, because the dried heads look good in the border.

For dried heads, cut while the colour is bright, which helps them hold it. Tie small bunches with a rubber band and hang them upside down in a dark, dry, airy place, such as a wardrobe or shed. They usually dry in three to five weeks and keep for dried arrangements and wreaths.

Common problems

Leaves yellow as the flowers open. This is normal at flowering time, so leave the leaves to wither (see Three mistakes).

Leaves but no flowers. A warm winter, deep shade or leaves cut early the year before can stop bulbs flowering. Chill bulbs before planting in the subtropics and move clumps into sun.

Stems leaning or flattened. Wind flattens the tall stems, and shade makes them weak and leaning; plant in a sheltered, sunny spot.

Alliums coming up beyond the bed. Seed and flower-head bulbils spread the plant, as under Weed status, state by state; lift unwanted clumps once the leaves die. For rotting bulbs, see Three mistakes.

Pests and diseases

Alliums are usually trouble free in a sunny border, and most problems are the same ones that strike edible onions.

Onion thrips (Thrips tabaci). Widespread in Australia and abundant on onions and garlic, these tiny insects leave silvery streaks on the leaves. Spray insecticidal soap late in the day, away from open flowers. Read more

Downy mildew (Peronospora destructor). It thrives in cool, wet weather, starting as pale yellow patches on the leaves that turn greyish-purple with spores. Space bulbs for airflow, water at soil level, and bin badly affected leaves. Read more

White rot (Sclerotium cepivorum). It rots the roots and coats the bulb base with white fluffy fungus. Its tiny black resting bodies stay in the soil for years (see Three mistakes). Lift and bin affected bulbs with the soil around them, and never compost them.

Onion rust (Puccinia allii). Bright orange or dark brown bumps form along the leaf veins. It is worst on garlic and chives, and its spores spread on wind and rain splash. Remove affected leaves as soon as you see them and bin them, never compost. It is not known in Western Australia, where any suspected onion rust must be reported to the state agriculture department.

Garden snail (Cornu aspersum). Widespread in Australian gardens, snails and slugs chew young shoots. Hand-pick on damp evenings, or scatter bait thinly by its label, never in heaps, and keep dogs away from the pellets and packet. Read more

Prevention first

• Plant only firm, clean bulbs, and bin any that are soft, mouldy or blemished.
• Clear away spent allium leaves once they are dry, because plant debris carries downy mildew.
• Move soil and tools from an infected bed only after cleaning them, because white rot travels in soil.
• Check new shoots on damp winter evenings for snails, and leaves in spring for thrips.

Tips

1. Store spare bulbs over summer in an old stocking hung in the shed, which keeps rodents away from them.
2. Chill bulbs away from ripening fruit, because the ethylene gas it gives off can make the flower buds abort.
3. Grow on the tiny bulbils from a flower head in a pot of gritty mix, 2.5 cm apart and 1 cm deep. They take several years to reach flowering size.

Due to quarantine restrictions and our shipping policy, we cannot send allium bulbs to Western Australia or Tasmania.