Potato Onions

It is my understanding that onions, as we know them today, are a fairly recent phenomenon. If my information is correct, domestic onions were not originally the single bulb plants we see nowadays. The single bulb onion seems to be a fairly recent "innovation" designed to make them larger and easier to harvest by mechanical means. Historically, onions were smaller multi-bulbed plants a bit like garlic but with each bulb being a distinct entity joined at the base rather than in a clove. The idea was that you did not need to grow the onion from seed. At harvest time you just broke off a bulb from the main bunch, planted it back, and then took the remainder away to be eaten. Hence the name "Potato Onion". This is a much simpler process if you are doing things by hand but not if you are harvesting mechanically.

As was typical back then, each region apparently had their own locally adapted Potato Onions but the development of the larger single bulb types, and the ready availability of seed from them, drove most of the Potato Onion cultivars into extinction. A very small number of the varieties hung on in some places (particularly North America) and you can still get them - but they are not common. Phyto-sanitary regulations prevented me from importing the bulbs themselves (I am in the UK) but I did manage to find and order some seeds. The resulting onions were quite small and did not split nearly as well as the sales pitches would have you believe. They also did not do well in my garden. This was probably not the seeds fault as they were not adapted to my local climate and since Potato Onions, by definition, propagate vegetatively the seeds were probably not all that trued up.

Once I had heard about the concept, I was determined to have some locally adapted Potato Onions. Given the disappointing results of my initial attempt to obtain worthwhile Potato Onions from seed, it seemed that the only reasonable way forward would be to breed my own. So, I resolved to try and resurrect a proper locally adapted Potato Onion.

The ultimate goal is to have a Potato Onion that can be planted in late autumn or early winter as a small bulb - basically an auto-generated onion set. By the end of the season, the planted bulb should have grown into a reasonably sized, onion with a number of smaller bulbs around the base which are suitable for next years replanting. The variety should also be able to set viable seed if it is permitted to generate a seed head. The simulated Potato Onion image at left illustrates the ideal.

An additional aspect of the goal is that, if there is any interest, any varieties produced will be released into the public domain as open source.

Caveat: The yearly results are reported towards the bottom of this page. The year of 2023 was the first time the output of the project was felt to be sufficiently interesting to be worth reporting. The project may yet come to nothing - there are many things that can still go wrong. For example, besides disease and climate issues, the onions that split so well this year (and previous years) could resolutely refuse to split again in the future and, hence, the reported varieties would be useless as Potato Onions. It is early days yet.

So, the decision has been made, I'm going to rebuild a locally adapted Potato Onion for my climate - but where to start? Well, I did get some (very modest) results from the purchased Potato Onion seed and so those plants could be used to add some useful traits into a genetic line. It also occurred to me that the many single bulb onions we have today were likely to have been originally bred from various Potato Onion varieties and so may still have those old "splitter" genes buried deep within them. I have noticed in the past that the bulbing trait does show up from time-to-time - particularly if you mogrelize them by letting them cross in with other varieties. In addition, I have another ongoing project to breed onions for long keeping traits and so have a ready stock of reasonably genetically diverse seed to apply to the project.

So I set about breeding a land race Potato Onion adapted to my climate. I am an aficionado of Joesph Lofthouse's promiscuous pollenation plant breeding methods and resolved to use his techniques for the project. This is just a fancy way of saying that while I was (and still am) madly chucking genes at my Long Keeping Onions project, at the end of every season I would separate out the ones that looked kind of "splitty" into a separate line. I have been replanting, interbreeding and culling the resulting hybrids for some years. The continuous selection pressure of that process is finally beginning to move things in an interesting direction. You can see the results from previous years further down this page, but first, a short discussion of the breeding technique used.

Breeding Technique

Looking at it logically, since onions are biennial, in an on-going Potato Onion breeding project there are actually three categories of breeding candidates under cultivation at any one time.

1. The seedlings which result from the planting of seeds (year 1)
2. The single bulbs resulting from the previous years seedlings (year 2)
3. The bulbs that have made it out of last years category 2 culling process (year 3)

The first category is the onions which result from the planting of seeds. These will hopefully produce an onion bulb of reasonable size. I have never observed an onion started from seed split into multiple bulbs in the first year. They seem to want to put all the energy they have into producing just one bulb.

The second category is the plants resulting from the single bulbs planted from the previous years seedlings (last years category 1). By the end of the second year these will hopefully have divided and produced multiple bulbs. The majority do not split and will just set seed since it is now their second year. The bulb is usually inedible after this point. For most of them, trimming off the scapes and not letting them set seed does not seem to encourage division into viable Potato Onions. They just devote their energy into producing new scapes.

The third category consists of the very few candidates that have made it out of the previous years category 2 culling. Note that these plants are in their third year by this time. These are, hopefully, viable Potato Onion candidates and have been observed to divide in the category 2 season. Of course, in the first year of category 3 there are only very few bulbs of any one new variety since they came from a single bulb that split into two or three. These bunches (groups) are split apart and replanted so as to increase the numbers and observe how they fare over time. Of course, the fact that a bulb split the previous year does not necessarily mean the resulting offspring are prepared to do so again in the following season.

I suppose the bulbs remaining after the category 3 culling could be considered to be a fourth category. However, I must admit I do not keep records of which category 3 bulb came from which group - I don't much care for that sort of thing. At the end of the season I just split apart every viable category 3 Potato Onion group and store them together. They will all get planted out randomly the following spring. The idea is that, ultimately, they will either work or they won't. Having a detailed pedigree is of little use since once I have a Potato Onion that I intend to run with I can just propagate from that bulb alone - its pretty easy....

.... and thats the final part of the breeding program. One useful thing about seeking to breed a variety that will ultimately be vegetatively propagated is that truing up the line is trivial. Once you obtain a locally adapted cultivar which works, then you can just split that variety in order to obtain identical copies. So that is one factor working in the projects favour - although it does feel a bit like cheating. Of course, long term vegetative propagation has its own problems - thus the requirement for the resulting cultivar to have the ability to set viable seed as well.

Results

The Potato Onion breeding project has been in progress for quite a few years. Only recently have the results been such that they are worth documenting. You can find a write-up on the results from previous years listed below

• The 2023 Potato Onion Report
• The 2024 Potato Onion Report