April 25 - I recently received this e-mail query:
"I overwintered Walla Walla onions for the first time this year. I planted them last September
and they are looking good, except they have recently begun to develop a stalk with a head.
"What now? Should I (1) cut off the heads like with garlic, and then wait for July, or (2) just sit back and do nothing, or (3) start to think about harvesting these guys?
"I have received different kinds of advice from different people and am ready to have you decide the issue."
The onions that are developing a stalk are going to seed, or "bolting". They may bulb up a little, but they're not going to form big onions. If the majority of your overwintered onions are sending up seed stalks, it's usually an indication that the plants were too large heading into winter. Perhaps you fertilized them too heavily when you planted the seed. It could also be the case that the sowing date you used was simply too early for your location.
On rare occasions this can just be the result of an extended period of unsettled spring weather.
With next year's crop, try either sowing a bit later (maybe try two sowings 1 and 2 weeks later than you did this time), or else fertilize less. The target is to have the plants be less than a pencil's thickness going into winter. Actually, finding the correct sowing date for overwintered onions is probably the trickiest thing about growing them!
It gets even trickier when you realize that specific varieties of overwintered onions mature at different times. Walla Wallas mature in early July (in my garden), as do a few others; but most types mature about a month earlier than that.
Onions that are going to seed are still edible, but if you let them flower and form seed they'll draw energy from the bulb (such as it is) and direct it to the seeds; so at that point the eating quality will go down. I'd probably harvest them by the time they've flowered at the latest.
You might find it helpful to read my article about growing overwintered onions.
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This page was last updated November 18, 2013