Bottom Heat for Germination


The growing rack is filling up. The bottom shelf is now exclusively a “hot box”, where the most heat-loving seeds go to germinate. Yesterday I added three kinds of basil (Tulsi or sacred basil, Genovese and sweet Italian) and greek oregano to the already resident eggplant, peppers, parsley and rosemary.

The second shelf is the medium temperature germination area (around 60-65F), where I added scallions, more garlic chives, rue, sage and lemon balm to the onions, leeks, chives and thyme and burnet, among others.

The third shelf is the seedling area with some room for seeds that like it cold for germination, like borage (around 55F).

I fiddled around with many way to give the heat-loving seeds their desired temperature. I ruined most of the first batch of eggplant seeds by placing them underneath an incandescent bulb: they got dried out, then I watered them, then they dried out again, etc.

Bottom heat is of course the best, I knew that. The electric heatmats that can supply it most evenly are $30 for one the size of one flat (10×20″) and $40 for one the size of two flats (20 x 20″, which is the kind of real estate I need at the moment). And that is without thermostat.

But first I wanted to build something myself. After some experimentation – during which I nearly cooked some seeds – I came up with this:


I used a double spotlight (part of the previous owner’s decor), with two incandescent bulbs and maneuvered each into a wooden wine case (came with the canning jars I got on Freecycle). On top of the boxes I placed two metal fridge racks (picked up at the landfill). The plugs and pots go right on top of those.

The temperature is of course not evenly divided, but that’s good. The soil in the pots right on top of the lamps is hotetst: 80F, perfect for peppers and eggplant. The pots more off center are about 70F and the ones to the side are 67F or so. It makes for some fun puzzling. The available area isn’t quite two flats, but close.

My only concern is the energy consumption. Those two lamps use 120 W. A heatmat consumes very little: about 45 W (for the 20×20″ one). The lamps are ineffecient: if they’re on for a month (and I keep them on at night), then they’ll consume 108 KWH {UPDATE} sorry, miscalculated: it’s really 86.4 KWH. The heatmats would make for only 32.4 KWH… To be continued.

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  1. Wow! Fantastic array of seedlings started. I can’t help but have that nagging little feeling with so many seedlings….how would I ever plant so many when it comes time? Back breaking work and with the little ones, you have to be so careful with your timing. I am jealous of your zeal.

    I am anxious to see how your garden comes out this summer. We are just now thinking about sowing some seeds in our little pots. We are not as ambitious as you though. :)

    Barb -Harmony Art Mom

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