More on Heat Mats

Flat of Salad Greens

Geoff posted last week about the heat mat set up he is using to start some pepper plants, here.  I use a heat mat and grow-lights as well to start peppers, tomatoes, and other vegetable seedlings that need a jump start, and I’ve also found the set up useful to give some bottom heat to my sweet potato starts well ahead of the time I need to get my peppers started.  Since I don’t need very much space for the sweet potatoes, I use the mat and lights to grow some salad greens, too.

I’ve already talked a couple of times about the heat mat/grow-light setup I use.  Here I talk about the set-up, in general, and here about using the lights for salad green production.  In this post I’ll explain an inexpensive temperature control I use to regulate the heat output of the mat.

I’m just about ready to start harvesting some greens as you can see in the top picture.  I’ve got two flats that are putting out very good growth.  I’ve got a third flat into which I seeded a lot of cilantro and basil.  They are sprouting, but I think I got the soil in that flat a little too hot and dry early into the process and most of the germination has been toward the edges of the flat. There is a little bit of new sprouting showing up, so we’ll see how it turns out.

The heat mat I have has no thermostat. That appears to be the case for many of the heat mats being sold.  If they do have a thermostat, they are factory pre-set and not controllable.   They sell temperature controlling shut off devices with soil probes to control the on/off heat of the mats.  I just saw one in a catalog for $40.00.  I invested $7.99 at my local Ace hardware for a light timer and it works quite well in lieu of a thermostat.  I’m maintaining a temperature at the bottom of the flats at between 75 and 80 degrees by using the timer shut off mechanism to turn on the heat mat for 30 minutes every two hours.

Inexpensive Light Timer

Setting the timer is very simple.  There are 48 on/off buttons – down is on, up is off. So having every fourth one down has the mat cooking one fourth of the time and idle for an hour and a half out of each two hour period.  When I first started up the system I let it get too hot and I think I fried some of the cilantro and basil seeds.  As the cilantro is a free saved seed, it’s not too a great loss.

Thermometer, Sweet Potatoes, and Salad Greens

I’ve got the heat for the system balanced out, and now it’s very stable.  In addition to the three flats, I have a couple of sweet potatoes in jars that are putting out a lot of root and just starting to put out some leaf buds.  Hopefully, I’ll get enough slips for this year’s planting

About the end of February, I’ll move any greens that are left into the sun room inside my south facing glass patio doors.  I’ll start three new flats with onions, leeks, and shallots, and when those sprout, I’ll move them into the sun room and use the heat mat and grow-lights to start peppers, tomatoes, eggplant, some of my cucurbits, and whatever else I can fit in.

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