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Permaculture plant: Perennial Onions


(Allium cepa var. aggregatum)

Potato onion bulbs and seeds. Photo by Maude Faruggia

Despite their name, the only thing potato onions have in common with spuds is the way in which they are planted. While potato onions can be grown from seed, they are most commonly grown by sowing a bulb of the previous season’s crop, in the same way that potatoes are grown from a previous season’s tuber.

Also known as multiplier onions, pregnant onions and a variety of other names that allude to their almost magical ability to grow a clutch of baby onions from just one bulb, potato onions are a valuable addition to a permaculture garden or food forest. This is because unlike biennial onions, they do not need to be grown from seed each year.


They like free draining soils, so growing in rows on a mound is a good idea. They don’t mind a bit of crowding with their fellow onions, but dislike jostling with competing weeds, so weeding rows well is essential. They are a little less fussy about planting time than many other alliums and can be sown either in autumn or spring, though harvests from the former are more bountiful.

They have very few common pest or disease problems, and their beautiful big blooms are a beneficial insect attractor. They are cold hardy and frost tolerant, but some varieties are sensitive to daylight hours, which can inhibit bulbing if they are grown at the wrong time of year in the wrong climate.


Potato onion harvests alternate between large and small bulbs each season. For example, plant a large bulb and you’ll find that you harvest a clutch of smaller, more slender bulbs. Plant one of these smaller bulbs the following season and you’ll find you have just one or two fat larger bulbs come harvest time. Seed heads are a sight to behold and can form part of an ornamental garden. While seed can be saved and sown, they do cross with other alliums so unless exclusion is practised, seeds may not grow true to type. Allowing plants to set seed for future sowing can also mean losing a few bulbs and bulbs going woody, so practice seed saving with this in mind.

Mature bulbs can be harvested when the first signs of flowering occurs and will need to be cured in a cool, dark and dry spot (in much the same way as garlic) before being stored.


Potato onions store well and have a very similar flavour to brown onions. They have much better storage properties than their relations, the shallot, and are generally larger (even the small bulbs), making them a great option for those wanting to grow their own supply of general cooking onions year-round.


(Allium proliferum)

Egyptian walking onions. Photo by Ginn Tinn

These strange and wonderful onions (also known as top-set onions or tree onions) are very similar to potato onions, with one major difference: they ‘walk’ to a new patch each year by growing a little bulbil from their flower stalk!


Egyptian walking onions grow in much the same way as potato onions, but can be grown from either a previous years bulbs or bulbils and prefer to be planted in autumn or winter.


Bulbs can be harvested once bulbils have set foot in the soil and the plant is beginning to die off. Ensure bulbils are left in situ (or moved to a new bed) when harvesting main bulbs. Green tops can also be used like spring onions during the growing season.


See potato onion.


(Allium fistulosum)

Evergreen bunching onions going to seed. Photo by BMJ

These green onions (also known as Welsh onions or scallions) propagate themselves by ‘bunching’ and can be sown almost all year round. They’re always welcome in our garden, as while they will self-propagate for many years, we eat them so often we need quite a supply of plants to ensure we don’t eat the whole bunch!


Slender bunching onions are a lot less fussy about growing conditions than their bulbing cousins. They can be grown quite successfully in small pots, or are just as happy amongst a guild of herbs in the ground. They can be sown from spring to late autumn.


Harvest fatter onions gently, being careful not to remove any baby shoots with them. These babies will go on to become the fat stalks you pick in the future. To avoid this problem completely some people just harvest plump green stalks and leave the white part and roots in the ground.


Green onions are meant to be eaten fresh. They can, however, be dehydrated and stored for later use or frozen if you really have a glut, however leaving them in the ground to propagate more baby onions is perhaps a better option.


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