The Backyard Larder

A place to explore and buy perennial vegetables and other food plants.

The Perennial Potato Onion

In the South Devon and Botanical Society May Show of 1851 you could win a prize of one shilling and sixpence for the ‘best dish of potato onions’. I’m not sure I’d win any prizes for mine but they have in fact done better this year than previously, thanks to further additions of compost to the soil. Onions like a rich soil!

potato onions in seed tray

Potato onions are similar to shallots in that they grow in clusters of bulbs, some of which can be replanted for the following season’s harvest. They are typically rounder, may be bigger and they have a stronger flavour than most shallots (which are generally known for their mildness).

Potato onions ready to harvest

Potato onions were widely grown in Britain in the nineteenth century, especially in Devon, falling out of favour in the twentieth, but now being sought out again as interest grows in perennial vegetables for sustainable food production. They seem to have fared a little better in North America where they also go by the names of hill, mother or pregnant onions (not to be confused with the poisonous but fascinating pregnant or sea onion, Ornithogalum caudatum). I’ve also read that varieties of potato onions not found elsewhere may be found in Finland, Russia and Estonia.

Close up of potato onions growing

To grow potato onions you have to plant potato onions. The usual advice is that you need to plant a small one to get a big one, and if you plant a big one you’ll get a cluster of smaller ones. That doesn’t seem to be exactly it from my experience. I only planted small ones last autumn (as I hadn’t grown them too well the previous year) but most of them developed into clusters of medium-sized bulbs (with some medium-sized singles). Maybe planting large bulbs would have given me clusters of prize-winning bulbs! But the advice still holds that it is best to plant a mixture of sizes in order to get some bigger ones to eat and some mixed sized ones for future planting.

Potato onions

I’ve read reports on North American websites of potato onions reaching 10cm in diameter. My biggest bulbs have only been just over 5cm; they may be genetically small as I got the original bulbs from Poyntzfield Herb Nursery who describe them as small. But they do store extremely well (in cool, dry conditions but not in the fridge) and can be planted in autumn for an earlier crop. Not all varieties are reported to store well and the largest bulbs are often said to store badly – also not all varieties are hardy enough for autumn planting. So whilst I’d love to have big potato onions, I’m very fond of these reliable doers. I aim to build up to big harvests in future years by replanting most of my bulbs in a variety of spots on my plots and lavishing some attention on them (hopefully they will become significantly bigger in the process).

potato onion split from cluster

Actually you can also sow potato onion seed – if you can get any. They do flower and produce seed occasionally. You may be able to get some seed from plant breeders such as William Whitson or Kelly Winterton in the States. Or if you can get some bulbs raised from their seed, you are more likely to get seed on your own plants as the ability for sexual reproduction won’t have been lost through generations of vegetative reproduction.

This led me to some ‘perennial potential’ musings…..Potato onions are classified, along with shallots, as Allium cepa aggregatum. In other words they are a form of the common onion. I’m not sure if common onions originally arose as a sport of these multiplying types or visa versa. I’m not sure that anyone knows as Allium cepa doesn’t exist in the wild. But Madeline McKeever of Brown Envelope Seeds mentioned to me on Twitter that some of her Ailsa Craig onions split to form both a flower stalk and a new bulb in their second year. Do your onions do that? It made me wonder if one could select for perennial traits amongst ordinary onions.

Finally this link and this one are interesting too – instructions for how you can eat any common onion and also grow on the very same onion for next years’ crop!

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