Introduction and description
Tree onions, Allium cepa ×proliferum, are similar to common onions (A. cepa), but with a cluster of bulblets where a normal onion would have flowers.
They can be classed from a nutritional point of view alongside onions and garlic.
Although we have provided this entry in order to help in identifying this plant, the observations for it are to be found with the more general onion category.
Genomic evidence has conclusively shown that they are a hybrid of the common onion and the Welsh onion (A. fistulosum). However, some sources may still treat the tree onion as A. cepa var. proliferum or A. cepa Proliferum Group.
Tree onion bulblets sprout and grow while still on the original stalk, which may bend down under the weight of the new growth and take root some distance from the parent plant, giving rise to the name "walking onion".
The bulblets are usually marble-sized, between 0.5 cm to 3 cm in diameter. They can vary in flavour; some tree onions are very strong flavoured, whilst others are relatively mild and sweet. The underground bulbs are particularly tough-skinned and pungent. They may be quite long, like leeks, or in some types may form bulbs up to 5 cm across.
Young plants may be used as spring onions in the spring, and the bulblets may be used in cooking similarly to regular onions or shallots, and preserved by pickling.