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Growing from Seed

Hardening off seedlings...when?

18 years ago

I've read many of the threads and understand how to hardenen off my seedlings but I can't find WHEN to do it. How big should the plants be, or does it depend on the outdoor temps? My seedlings have their second set of true leaves, are in 4" pots and we have temps in the low 50's during the day and 30's at night. Thanks!

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Comments (3)

morz8 - Washington Coast
18 years ago
It depends partly on the plant....tender annuals or hardy perennials?

Best - wait until after chance of frost. (very tender annuals i. e. impatiens, I wait until night temps will stay above 45) We had frost just last night here on the coast, and since it's dropped to 40 from 55 under clear skies already this evening...I wouldn't be surprised to see light frost tomorrow morning.

It shouldn't be much longer, my last frost date in 2005 was March 9th and we've already past that date :)
morgan_5
Original Author
18 years ago
Thank you! Only perennials so far. The seedlings I have ready right now are Gaillardia and Salvia. Except for the floppy leaves on the Gaillardia (which I asked about in a previous post) they are looking great. This is my first year growing these from seed though so want to get the timing right.
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hello, I would keep them inside tonight. 49* will not hurt the plant but it's not great 41* might damage your plants or at least it could stunt them. Try putting the plants in a shaded area outside for a fw hours then move them to the sun for about a half hour increase the time outside and the time in direct sun until you leave them out 24/7 when night time lows are 50 - 55 and all danger of frost has past. This process should take about two weeks unless the danger of rost in your area has not passed yet you can plant them out when there done.
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I was not going to leave them overnight. I also have a large cold frame that is covered and has heating cables in the soil and I would put heat mats (for seed starting) inside also. Worse case I could easily cover it with blankets. Unless temps go below 30 I am ok. They would probably be fine under 25 - Would just toss in a small electric heater and leave it running all night. I am hooping to get them in the ground in about a week. Do you harden off for cold? I never have - so not sure. Meaning I put out on warm sunny days.
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calistoga_al ca 15 usda 9
18 years ago
The hardening process takes several days each day spending more time outside in a shady wind protected area, not over night. If you are only a week or so from your last frost, I would begin hardening off now. Al

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