A series of questions came in from Jaci this week about saving onion seeds. Her questions are really about growing onions for seed-saving. There is a difference (and she knows it). So let’s dive in to her questions:
Do different varieties of onion that mature to harvest size at different times (60 – 120 days) do the same for when they flower? Or do they all just flower about the same time.How far apart should the different varieties need to be from each other?
If I plant 4 plants (the same variety) close to each other and allow them to flower, can I use a netting over them to contain the pollination to just those 4 plants?
How much of onion pollination is insect, how much wind, or how much relies on self pollination?
Okay, Jaci. Let’s look at your first question:
Do different varieties of onion that mature to harvest size at different times (60 – 120 days) do the same for when they flower? Or do they all just flower about the same time.
It depends on growing conditions and stressors. In theory onions with different days to maturity rates would flower at those different rates as well, but drought or heat stress can cause onions to prematurely bolt to seed. You could try for seed saving based on which plants go to seed first, but I wouldn’t recommend use days to maturity as a reliable factor.
Next:
How far apart should the different varieties need to be from each other?
According to The Seed Garden (our affiliate link) by the folks at Seed Savers Exchange, onions and other alliums require an isolation distance of 800 feet to half a mile to prevent cross contamination from other varieties. Since I am guessing you don’t have that much space (who does?!), I suggest only letting one variety go to see each year and cut down any flowering stalks from the other varieties flowering at the same time.
Next Question(s):
If I plant 4 plants (the same variety) close to each other and allow them to flower, can I use a netting over them to contain the pollination to just those 4 plants? How much of onion pollination is insect, how much wind, or how much relies on self pollination?
I’ll answer both of these questions about pollination all at once. Since onions are insect-pollinated, you’d have to trap some bees in your netting for that to work. Also, Seed Savers recommends at least 5 plants for viable seed. That said I’ve saved seed for green onions from one plant and those work. It’s just less genetic diversity in your supply.
I hope this helps you save seeds from all the varieties you want, maybe just not all at once. Good luck and keep us posted.
Thank you so much! This gives me a plan…..and talking to a neighbor that is a master gardener (I never knew that) that knows the layout of my garden, she thinks it is possible. Luckily, I have a berry bed and orchard far away from my veggie garden which is 60×120 and will have a high tunnel up within a month. She suggested to grow my “seed onions” 5 or 6 to a group and space each variety as far away as I can from each other. Then as the flowers start to develop cover all of them with insect netting. Then as the flowers develop open up just one variety and let the insects play. Then cover that one again and open another one. She says she believes that I may get a few days to a week between varieties when the flowers are receptive. So paying very close attention and nature cooperating, she thinks I can successfully keep any cross-pollination to almost nil. I will experiment in 2026 and let you know how it goes. But she did say I may not get as many seeds from each plant, but should get more than I need. I grew over 400 onions this year – not for harvesting, but for vole control – and it seemed to help a lot growing onions on the sides of each of my 4 potato rows.
This sounds like a great experiment. In theory, it should work. And it will be even easier if your onions flower at different times. Keep us posted on how this goes.