How cold is too cold for onion seedlings?

rhubarb_stalker(Z5b Western MA)March 24, 2011

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.

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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.

    Bookmark   March 27, 2011 at 1:12AM
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seysonn(8a WA/HZ 1)

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.

    Bookmark   March 29, 2011 at 6:55AM
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