Tree onions - Allium x proliferum
Tree onions, top setting onions, Egyptian onions, walking onions… there are many names for what is probably the most useful and hardy of the perennial onions. Recent evidence has shown them to be a hybrid of the common onion, A. cepa, and Welsh onion, A. fistulosum. There are several named varieties going around - we currently grow ‘Catawissa’ and ‘Kiwi’ varieties plus an unnamed variety we picked up many years ago before we knew there were different kinds.
These are the Alliums we use most in our day-to-day harvesting and eating from our garden. There are fresh tender green leaves almost all year round and the top-sets and below-ground bulbs can be used just like common onions (though the top-sets are fiddly to prepare). If left on the plants, the top-sets or bulbils will sprout and grow. The stalks bend under the weight of the new growth and take root some distance from the parent plant, giving rise to the name ‘walking onions.’ The underground bulbs also divide as they grow making tree onions a very prolific producer.
Like the other alliums, tree onions will naturalize in the forest garden - they are extremely hardy, grow well in dappled shade and need little attention when established (Newly planted bulbs should be weeded however, as plants don’t like competition when they are young). Clumps will expand year on year and the top-sets will spread. Bulb clusters can be dug up, divided and replanted (or eaten) in summer and autumn. Alliums generally grow well with most plants, especially roses, fruit bushes, carrots, celery, celariac, beet and chamomile, but they inhibit the growth of legumes.
Bulbils for planting will keep in the fridge or somewhere cool for several weeks (wrap in paper) if they have been dried out first. They should be planted directly in the ground between July and December, just below the surface and 15-20cm apart. They can also be planted closer together in pots, but will need transplanted to the ground when they start producing top-sets.