With my summer garden winding down, I turn to thinking about next year. I'm very comfortable starting from seed and growing nightshade vegetables like tomatoes, peppers and eggplant by this point. This year I added cucumbers, summer squash, greens, garlic and carrots to my garden. Next year, I want to try a few more new vegetables. And, I'm thinking about growing onions in the 2011 garden. For some reason I feel like onions are kind of confusing: long day v short day v intermediate, bunching v green, sets v transplants v seeds, etc. Thus, I've turned to books and the internet to try to sort this all out. This is what I've learned:
What's the difference?
As far as I can tell there are 3 "types" of onions: Bulb, bunching and multiplier/perennial onions. The bulb type are what we generally buy in the grocery store (they're are the option to choose if you want storage onions) and one seed/set/transplant will give you one onion. Bunching onions are basically "green onions" as they don't form large bulbs. And, finally, multiplier (or perennial) onions are like the bulb onions but they--as their name implies--multiply and create their own sets. Shallots and potato onions do this by creating clusters that you separate & divide, while top-setting onions, like the Egyptian walking onion, create bulbets that form on the top of the stem which take roots
Sets, Transplants or Seeds?
Sets are tiny bulbs, about the size of a marble without any sprouting, that were started from seed the year before. These are the easiest way to plant onions, but transplants actually offer better success and store better. Sets can be planted before the last frost, but the soil needs to be rather dry and a bit warm otherwise they can rot.
Transplants are just like any other seedling/plantlet...they are baby plants. You can buy these (although I don't think I've ever seen these in the nurseries around here) or start your own from seeds. These tend to result in bigger onions than sets and have few pest issues. When the danger of frost has passed, plant harden offed transplants in the ground, but don't bury too deep.
Seeds often allow the greatest variety of cultivars. Start them indoors 8-12 weeks before transplant date, but if you're blessed with a long growing season, you can direct sow outside.
If you're doing bulb onions (by seed, transplant or set) you'll need to match to your summer daylight. If you're north of a line from North Carolina to San Francisco, plant long-day cultivars. If you're south of it, plant short-day cultivars.
No matter what type of onion you choose, they all seem to need well-drained soil with at least half a day of direct sun.
I think, should I plant onions next year, I'm going to go with seeds of bulb-type, long-day cultivars that I'll start indoors. The idea of perennial onions is tempting (I love stuff that you just plant once!) but I'm not sure where I would put them.