Germination Temperature Above 90 Degrees Bad for Seeds?

alex818(z9 CA)October 21, 2009

So the other day I bought a germination heat mat with a 72 cell seed starter kit and dome. Im using Rapid Rooter plugs in them trying to grow Bhut Jolokia peppers. The heater does not have any kind of a regulator so I wasnt sure how warm it was getting. I bought a little glass aquarium thermometer and inserted it into an empty plug. Today I noticed that the temperature had risen to about 95 degrees so apparently it had been running at around that temp for almost 2 days. Today I used some wood to raise the container a little higher so its not actually touching the mat but the air in between warms up heating the container and making it about 89 to 90 degrees now. Does anyone know much heat the pepper seeds can tolerate before going bad? Is 89-90 degrees still too warm?



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rds040800(Zone 9)

Ideally you want to keep it between 80 and 86. Here is a link to an article outlining this with germination rates at different temps. You just have to convert from Celcius to Farenheit.

    Bookmark   October 21, 2009 at 7:44AM
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The heat mats I have say they keep the tem. at about 20 degrees above room temp.Whatever that may be.
So I'd keep an eye on the temp. if it gets warmer or cooler in that room.
They set them like that going by the assumption most rooms are 75 degrees or so and your sprouter would be a little lower than room temp. without the mat.
you can buy a thermostat for heat mats-$$$$$$$.

    Bookmark   October 21, 2009 at 12:22PM
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rdback(Z6 VA)

Something else you can do is cover the heat mat with a towel or 2 or 3 etc until you get the temp down into the low 80's. By using the towels, it eliminates potential temperature fluctuation caused by airflow between the mat and the seed tray.


    Bookmark   October 21, 2009 at 12:29PM
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The hydrofarm mats I use indicate that if you want the root area to be 90+ leave the mat on 24x7. IF you want it less than that you need to unplug them for a certain number of hours each day.

The easiest way to control it is with a single thermostat that shuts off the power when the ideal temp is reached.

Alternately with a thermometer one can do as Rick suggests and place insulating layers between the mat and the flat. This slows the heat transfer and allows more time for heat to dissipate from the potting medium. It's more trial and error, but gets the job done.

FWIW, I can't imagine pepper seeds having a germination issue with the mat left on 24x7. A mat intended for horticultural use simply shouldn't raise the temps in a flat too high for seeds, like peppers, that prefer warm soils. With the hydrofarm mats I use flats with dome covers on and often under HID lighting and it doesn't get so hot that germination doesn't occur in a reasonable timeframe.

    Bookmark   October 21, 2009 at 3:55PM
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