How to Grow Tree Onion
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Tree Onion
Allium cepa var. proliferum
vegetableTree onions are perennial bulbing onions that produce small aerial bulblets (also called topsets) in clusters at the top of tall, sturdy stems instead of flowers. These bulblets can be replanted to grow new plants, making them a self-perpetuating crop. They are cold-hardy, unusual, and excellent for gardeners seeking novel or heirloom varieties.
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Example Tree Onion timeline · Pittsburgh, PA (Zone 6b)
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Plant Tree Onion
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Tree Onion
Around Jul 16≈ 90 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Tree Onion dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Zones 3-8; extremely cold-hardy and suited to cooler climates
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Dormancy & Emergence
2-4 weeks (spring) or overwinterBulbs remain dormant over winter or early spring; green shoots emerge as temperatures warm
In fall-planting regions, apply winter mulch (2-3 inches) for frost protection. Reduce watering until growth appears. Monitor for slugs and snails.
Vegetative Growth
6-8 weeksTall, sturdy stems (12-30 inches) develop with green foliage; plant builds leaf area and root system
Water regularly and consistently. Apply balanced fertilizer every 3-4 weeks or use compost top-dressing. Stake tall varieties in windy areas. Remove any flower heads that form.
Bulblet Formation
4-6 weeksStems thicken and clusters of small aerial bulblets (quarter to half-inch diameter) form at the stem tip, often in a nest-like arrangement
Reduce nitrogen; switch to phosphorus-rich fertilizer to support bulblet development. Maintain steady watering but allow slight drying between waterings. Support tall stems with stakes if needed.
Bulblet Maturation & Ripening
2-3 weeksBulblets develop papery skin and darken in color; foliage begins to yellow and die back; bulblets become heavy and may cause stems to bend
Reduce watering gradually as foliage dies. Allow stems and bulblets to dry in place if weather permits. Do not harvest until bulblet skin is dry and papery.
Harvest & Storage
Ongoing through fall and winterStems dry completely and bulblets are ready to separate and store or replant
Cut entire stem cluster when fully dry. Separate bulblets by gently breaking them apart or cutting the stem. Cure bulblets in a cool, dry location for 1-2 weeks before storage or replanting.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Use row covers during early growth; remove affected plants; apply neem oil or spinosad if infestation occurs; ensure good drainage to reduce adult fly habitat
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Spray with insecticidal soap or neem oil; increase humidity slightly to discourage them; remove heavily infested leaves
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Hand-pick, especially at dusk; apply diatomaceous earth around plants; use slug traps with beer or yeast; remove leaf litter and dense mulch nearby
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Ensure excellent drainage; avoid overhead watering; sanitize tools; remove and destroy infected plants; crop rotate; avoid planting in same location for 3+ years
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Improve air circulation; avoid overhead watering; apply sulfur or copper fungicide if needed; remove infected foliage
Uses
Unique onion flavor for cooking and pickling
CulinaryTree onion bulblets are small but flavorful with a milder, slightly sweeter taste than storage onions. They are excellent pickled whole, roasted, or minced into dishes. The edible foliage can also be used as a scallion-like green. [source]
Self-propagating perennial crop
CulinaryUnlike standard onions that must be replanted each year from seed or sets, tree onions regrow from bulblets, making them a low-maintenance perennial addition to kitchen gardens. Once established, they can provide onions for multiple seasons with minimal input. [source]
Ornamental and novelty appeal
CraftThe tall, distinctive stems topped with clusters of small bulblets make tree onions visually striking in gardens. They are excellent conversation starters and are valued by heirloom and unusual vegetable gardeners. [source]
Storage and preservation
HouseholdBulblets store well for months in cool, dry conditions and can be pickled for extended shelf life. The year-round availability makes them useful for winter cooking and pickling projects. [source]
Traditional allium health benefits
MedicinalLike all onions, tree onions contain sulfur compounds and quercetin with potential anti-inflammatory and antioxidant properties. They have been used in traditional medicine to support immune health and digestion. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest bulblets when the stem has dried completely and foliage has yellowed and withered. Cut the entire stem cluster at or just above soil level. Separate individual bulblets and allow them to cure in a cool (50-60°F), dry, dark location for 1-2 weeks. Store in mesh bags or paper in cool conditions (32-40°F, low humidity) for winter use. Replant bulblets in fall or spring depending on your climate. Some gardeners leave the smallest bulblets in place to multiply in situ over multiple seasons.
Fun Facts
- 🌱 Tree onions are an ancient heirloom variety that have been cultivated in Europe since at least the 1600s, and are mentioned in medieval herbals as unusual multiplying onions.
- 🌱 The bulblets are heavy enough that mature stems often bend or collapse under their weight, which is actually beneficial—fallen stems can root into soil and create new plants without any human intervention.
- 🌱 Tree onions are sometimes called 'Egyptian onions' or 'walking onions' because they can gradually 'walk' across a garden as falling, rooting stems create new plants at increasing distances from the original planting site.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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