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How cold is too cold for onion seedlings?

Posted by rhubarb_stalker Z5b Western MA (My Page) on
Thu, Mar 24, 11 at 8:00

I've got my onion seedlings in the cold frame, and nighttime temperatures are supposed to get down into the low 20's. How much cold can these little guys handle? I know I can take them out of the cold frame and put them into the garage, but I would like to avoid that if possible.

Follow-Up Postings:

RE: How cold is too cold for onion seedlings?

Depending on the variety they should be able to handle those temps. I am up here in Ontario Canada and last night my Redwing and Cortland seedlings were exposed to -6.5C (20F) in my unheated greenhouse. They are in cell packs and the grow medium just about froze solid and they survived and appear to be fine now. I don't know if this will adversely affect them later in their growth ie. bolting or thick necks, I guess I'll find out. We are having another very cold night tonight so I brought them inside, I don't want to push my luck.
They are about 9 weeks out from seed in 100 cell packs, about 2 - 4 seedlings per cell.
Hope this helps.

RE: How cold is too cold for onion seedlings?

Freezing temps should not be a problem. But I would try to mulch them with dry leaves/straw/ pine straw heavily to prevent from repeated short cycle freezing and thawings, as much as possible. This is the only reason for mulching the over-wintering garlics as well. The ground (in zone 5) will probably freez to a depth of more than a feet with or without mulch.

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