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Keep peas off the heating mats

Seed-starting station

In every part of gardening, there are inevitably setbacks when you try something new. My fancy seed-starting setup started off great, producing healthy onion seedlings and quickly sprouting lettuce and kale seeds. But the peas refused to come up. And when I poked in the dirt atop the latter, I discovered that every single seed had rotted in the ground.

Vegetable seedlings

Putting on my thinking cap, I came up with three potential problems. Possibility one --- peas hate stump dirt. Possibility two --- the year-old pea seeds just weren't viable. Or --- the possibility I suspected was actually the most relevant --- our new heating mats exceeded the maximum germination temperature for these cold-weather legumes.

Soil temperatureThe trouble was, I bought a cheap seed mat without a thermostat, and I soon found that the device runs a little hotter than the heating pad I'd been using previously. On a warm day with the heating mat on, soil temperature was right at 85, compared to a non-heated tray that clocked in closer to 72. Sure enough, 85 is listed as the maximum germination temperature for peas.

To test this hypothesis, I started another round of pea seeds, this time off the heating mat but using seeds from the same packet planted in the same stump dirt. Sure enough, three days later, this second round of peas had broken dormancy and were sending down roots. Success!

Moral of the story: keep peas off the heating mat but put everything else on the heating mat until they sprout. I'm curious to see what my new setup teaches me next.



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I have never used a heating mat before. I have always assumed that the seeds will just come up whether or not it is heated. Have you tested seeds side by side, one with the heat and another without? I'm curious if the expense and trouble are truly worth using heating mats.
Comment by David Wed Feb 24 09:24:30 2016

David --- It depends on the vegetable variety and your house temperature. We use wood heat, so winter temperatures in our trailer often get down to 40 degrees at night. That dramatically slows seed germination! In our situation, yes, I've done side-by-side trials and shown that seed mats are extremely handy for faster, more thorough germination.

That said, if you live in a climate-controlled house, you might get away with just putting flats in a warm spot like on top of your fridge or water heater. It just depends on how warm your house generally stays at night.... :-)

Comment by anna Wed Feb 24 09:46:07 2016
Anna -- That makes a lot of sense. Yes, I'm in a house with a thermostat but we supplement our heating with a wood stove as well. I just bought a couple of fluorescent bulbs that have a high Kelvin rating and I'm hoping that this will make the difference between having leggy seedlings that fall over and die and ones that actually survive to be planted in the garden.
Comment by David Wed Feb 24 10:32:20 2016