While air temperature is 74F in the house, soil temperature of my potted indoor plants can be 68F, because evaporation cools it down. Not only will some seeds not germinate under 80F,
I’m learning that even cool-weather crops, like collards just don’t thrive when they’re young, if the soil is under 79F. Some LED lights don’t put out much heat, others put out a little more.
When on the shelf below young plants, they can supply a bit of bottom heating to keep the soil from falling below 70F. Even with a heating mat that heats to 90F, soil temperature is still only 73F after an hour of heating.
I’ll have to check things tomorrow to see if more time heating increasing soil temperature. I expect it will. For comparison, I brought potted eggplants indoors.
While outdoors over summer, they produced eggplants about 8-10″ long and an inch and a half diameter. The same plant fruited indoors, (because it had been pollinated outdoors) and is now struggling to produce 4 x 6″ long and a half inch diameter eggplants.
In another case, I germinated cucumber seeds, planted what I could indoors and had a pair left over. They were the smallest. So I put them in a pot in the greenhouse.
The runts are now 4 times bigger than the indoor cucumbers. So, lower temperatures translate into slower growth, if not failure to thrive for indoor plants.
For anyone in northern zones, I advise seedling heating mats on lower shelves. Growing in a closet or grow tent, that can be warmed above common room temperature (72F) and/or a space away from exterior walls would be a good idea.
Sunlight really helps plants thrive, but a cold window slows growth a lot. I hope others can learn from my mistakes. 🙂
Whitewolf I’ve grown veggies indoors before, but then wondered what I’d do if the lights went out. How would I get fresh greens? Then I discovered sprouting like beans, alfalfa, lentils, broccoli. They even like to grow in the dark! You can buy sprouting seeds online.