Tree onion

Family

Alliaceae

Habit

perennial

Height

0.9 m

Spread

1.5 m

Growth

fast

Lifespan

10 years

First yield

after 2 years

Hardiness

zone 5–8

Shade tolerance

full sun

Soil

Sand, Silt

Soil moisture

moist – very wet

pH

6 – 7.5

Times apply to the northern hemisphere in a temperate climate and shift with altitude and cultivar.

A hardy, perennial onion for sunny to partly shaded beds on free-draining garden soil that is not too wet; once planted it stays in place for years. Planting time for the bulbils is September. How large the bulbs turn out depends primarily on vigour and site, and partly on the origin of the plants — cultivar names are barely used in Europe, so different strains circulate under the same designation. If you do not need it for propagation, keep harvesting the upper tiers; the stalk then does not topple and the stand stays put. Against weeds, letting trailing squash grow over the rows has proved itself in practice: squash is easier to keep in check than couch grass and buttercup.

It propagates exclusively vegetatively: instead of flowers the flower head forms bulbils, which sprout while still on the mother plant and in turn set further bulbils in a second and third tier. When the stalk topples under the weight, the upper bulbs root where they land and the stand migrates — hence the English name walking onion. All offspring are genetically identical to the mother plant, so a good selection stays unchanged for decades. The bulbils are taken off and planted without any pre-treatment from September of the same year. Practical accounts report that a vigorous mother plant yields twenty to thirty bulbils a year, with a further four to seven already forming inside each green bulb that has sprouted; two mother plants produced around four hundred plants within a year this way. Occasionally true flowers appear among the bulbils.

One of the few onions that works as a true permanent crop: instead of seed it forms bulbils, propagates itself without any help and yields more planting material every year than you can find room for. Because propagation is purely vegetative, a good strain once found is preserved unchanged — and because the flower head sets no seed, it does not escape by self-seeding.