How to Grow Tree Onions USA

Soil & Growing Conditions

Water: About 1in of water a week; MSU notes it does not thrive in wet or extremely heavy soils.

Growth Stages

Quick Facts

At a Glance

Harvest & Storage

When to pick: Topsets can be picked once they colour from green to reddish or purple (Penn State). Leaves can be cut like chives or green onions at any point while green. The underground parent bulb is edible but tough-skinned and pungent (MSU), and lifting it ends further growth from that plant.

Diseases

Pests

Tree Onion, Topset to Walk

A stem topped with bulbils, not a flower

Instead of a normal flower, the stem produces a cluster of small bulbils called topsets -- green at first. This is the defining trait that separates tree onion from every other allium in the collection.

Colouring as they mature

Topsets turn reddish or purple as they mature (Penn State), a visible cue that they're ready to pick, propagate, or leave to root where they fall.

The stage before it "walks"

As the topset cluster grows heavy, the stem dries, weakens and eventually topples under the weight -- moving the plant roughly 2-3ft across the garden as the fallen bulbils root where they land (Penn State).

The leaves are a harvest too

Leaves can be cut and used like green onions at any point while green -- a crop in their own right, separate from the topsets and the tough, pungent underground bulb.

Sources

1. Penn State Extension - Egyptian Walking Onions

   Heirloom perennial onion producing a cluster of bulbils (topsets) at the top of the stalk, green at first, turning reddish or purple as they mature. When the cluster gets too heavy the stalk falls over and takes root where it lands -- the plant "walks" roughly 2-3ft across the garden per year. Plant bulbils 2in deep in full sun; fall is the optimal planting season, though bulbils can go in any time the ground isn't frozen. Leaves used like green onions; topsets fried, cooked in soups, or eaten raw in salads; underground bulbs are edible but very hot, and harvesting them prevents regrowth from that point.

2. University of Wisconsin-Madison Division of Extension - Egyptian Walking Onions

   Allium x proliferum is a cross between the cultivated onion (A. cepa) and the Welsh onion (A. fistulosum), hardy in USDA zones 3-10. Instead of flowers and seed it makes a cluster of BULBILS (topsets) at the top of the stalk; if they are not picked, the stalk flops over under their weight and the bulbils root where they land -- which is how the plant "walks" across the bed, moving only 2-3ft a year. Propagate by breaking off bulbils and planting them no more than an inch deep and 4-5in apart. Plant in FULL SUN somewhere you are content to keep them long term, since they are perennial. Eat the tender young shoots and stems as spring onions, the small underdeveloped basal onions (VERY HOT), and any bulbils not replanted, which keep a few months in store. Pests: thrips can be a problem in hot dry summers but the damage is mainly cosmetic. Not susceptible to juglone.

These 2 sources are specific to this region. The full list of 5 sources behind this guide (Michigan State University Extension, Penn State Extension, Royal Horticultural Society and others) is in the references of our UK guide to tree onions; they describe the plant itself, which is the same wherever it grows.