How to grow tree onion
Overview
Tree onion (Allium x proliferum), also called walking onion or Egyptian onion, is a perennial vegetable grown for its edible leaves, bulbs, and top bulbs (bulbils). It is extremely cold-hardy and produces clusters of small bulbs at the top of the stem that can be replanted to propagate the plant. A low-maintenance staple for productive beds.
Varieties
- Egyptian Walking Onion — The most common form in Australian gardens; produces clusters of small reddish-purple bulbils at the top and forms a clump of bulbs underground. Very hardy and productive.
Soil Preparation
Prefers fertile, well-drained soil with a pH between 6.0 and 7.0. Enrich the bed with well-rotted compost before planting. Good drainage is essential to prevent bulb rot—raised beds or mounds help in heavy clay soils.
Growing Guide
Plant in full sun with well-drained soil. Space bulbils or divisions 20–30 cm apart, planting 2–3 cm deep. Autumn or early spring planting works best in most climates. Mulch to retain moisture and suppress weeds. Established clumps will multiply and require occasional division every 2–3 years to maintain vigour.
Care
Feed with a balanced organic fertiliser in early spring and again after the main harvest. Remove spent flower stalks to direct energy into bulbils. Divide clumps every 2–3 years to prevent overcrowding and maintain vigour; discard weak or diseased sections.
Companion Planting
Good companions include carrots, beetroot, lettuce, strawberries, and tomatoes—these benefit from the onion's pest-repelling properties. Avoid planting with beans and peas, as alliums can stunt their growth. Do not replant tree onions in the same spot as other alliums to reduce disease risk.
Common Pests & Risks
Thrips cause silver streaking and stunting—control with neem oil or insecticidal soap. Rust (orange pustules) can occur in humid conditions; improve air circulation and remove affected leaves. Onion root maggots are less common but can be deterred with crop rotation and diatomaceous earth.
Harvesting
Harvest leaves at any time once they are large enough to use. For bulbs (including top bulbs), wait until the foliage yellows and dies back in summer or early autumn. Lift main bulbs with a fork; top bulbs can be snapped off and stored. Regular harvesting encourages fresh growth.
In the Kitchen
All parts are edible: use leaves like chives or spring onions, bulbs as mild onions, and top bulbs can be pickled or cooked. Store bulbs in a cool, dark place for several weeks. The top bulbs have a stronger flavour and are excellent in stir-fries.
Troubleshooting
Yellow leaves: often overwatering or nitrogen deficiency—reduce watering or feed with seaweed extract. Rust (orange pustules): improve air circulation, remove infected foliage. Thrips (silvery streaks): spray with neem oil weekly. Bulb rot: caused by poor drainage; replant in raised beds. Poor bulbil production: insufficient sunlight or excessive nitrogen; ensure full sun and use balanced fertiliser.