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Vegetable Gardening

Can you over-heat seeds so they don't germinate?

7 years ago

I'm starting some seeds indoors using a heat mat. The soil got to between 87 and 92 degrees, which the peppers loved. The lettuce and chives didn't do so well. Half the lettuce sprouted. Some of one chives variety did too. None of the other chives variety germinated. I know they prefer cooler soils (75 degrees or so) for germination.

It has been over a week since I removed the heat from the lettuce and chives. The soil has been right around 75 degrees since. There is no new growth of the chives. Can high soil temperatues essentially kill seeds so they won't germinate even when moved to preferred temperatues? Should I just start a new batch?

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Comments (11)

theforgottenone1013 (SE MI zone 5b/6a)
7 years ago
Yes, heat can kill them. Lettuce and chives need no heat at all. If the room they are in is around 65 to 70 degrees they'll germinate just fine. And they don't need heat to grow once germinated.

Rodney
LoneJack Zn 6a, KC
7 years ago
I agree with Rodney. Not much requires a heat mat but some of the slower germinating seeds can benefit and germinate faster with one. Lettuce is not one of those. I seed lettuce and put directly under lights and they germinate in 2-3 days. If not up by day 5 they probably won't ever sprout.
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zzackey
7 years ago
Where do you live that you need to start seeds inside now and use heat mats?
Eric
Original Author
7 years ago
Colorado 5b. This being my first year, I messed up seed starting early on. Now I'm refining my methods so I don't have a debacle next year. Clearly a good idea because I killed my chives.
floral_uk z.8/9 SW UK
7 years ago
Is it too hot to direct sow your lettuce?
daninthedirt (USDA 9a, HZ9, CentTX, Sunset z30, Cfa)
7 years ago
Some nice tests exploring the effect of temperature on seed germination is here. http://tomclothier.hort.net/page11.html

Lettuce goes over the cliff at 80F. Even peppers are happier at below 90F. Amusingly, turnips, which are real winter veggies, and highly frost tolerant, are delighted to have germination temperatures as high as 95F.
Eric
Original Author
7 years ago
last modified: 7 years ago
It's more a question of, if I start my seeds in soil that is too warm (85 degrees for a week) then remove the heat (75 degrees), will they germinate? So far with my chives it seems not. Nothing is happeneing so I'm wondering if I killed the seeds.
Eric
Original Author
7 years ago
I made the mistake of asking my question in more than two sentences. I don't think many people are actually reading the question :)
theforgottenone1013 (SE MI zone 5b/6a)
7 years ago
Pretty sure I answered your question with my first sentence. "Yes, heat can kill them." If the seeds get too hot for too long it won't matter if you move them to cooler temps.

Rodney
Eric
Original Author
7 years ago
Sorry Rodney, you were one of the exceptions.
floral_uk z.8/9 SW UK
7 years ago
Eric, you asked 2 questions.

1. Can high soil temperatures essentially kill seeds so they won't germinate even when moved to preferred temperatues?

2. Should I just start a new batch?

I read both questions and all the answers. Rodney answered the first for you. My query was a continuation of the discussion and an attempt to get further information to help you with your second question.

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