Petunias can handle temperatures as low as 29 degrees (F)–a fact I’ve long applied to all cool season annuals. I recently checked cold tolerance for the specific varieties in my winter vegetable garden. Turns out, everything I’ve planted can handle temperatures as low as 20 with most surviving as low as 15.

Talk about relieved. Here in USDA Zone 8A, temperatures lower than 15 are rare. I won’t need to cover stuff nearly so often–if at all.

This garden is the result of two plantings–one back in August (cabbage, collards, chard, broccoli and Brussels sprouts) and another just a few weeks ago (spinach, mustard, two kinds of lettuce and more chard). Everything was started from seed indoors with 12-hours of light/day. I only had room on the heat mat for one of two flats, so half of the first planting had no bottom heat.

The heat mat keeps the soil around 72–roughly ten degrees warmer than the unheated cells on my indoor rack. Seeds sprouted MUCH sooner with heat. Everything was up within days with both plantings.

Half of the Brussels sprouts, cabbage and broccoli went in the ground. The other half went in big pots, 3 plants per pot. Comparisons are a bit unfair because the smallest seedlings went in the pots so I could keep up with them–another lesson learned. Collards and the first chard planting didn’t have bottom heat and were much smaller than everything else when they were planted.

The second planting was supposed to be an indoor salad garden. I used containers with four cells–the largest I had–and kept to one flat for the bottom heat. They came up fast and soon had to be moved to individual pots. That’s another lesson learned: Don’t let seedlings touch each other or get even a tiny bit root bound

Potting the seedlings increased the volume from one flat to two. I ended up moving half of each variety to the coldframe for a little experiment to see which did best. In a matter of days, the plants in the coldframe looked much healthier than those indoors under lights.

I open the coldframe when it’s in the sun to keep the inside under 90 degrees. The rest of the time, it stays closed. I plan to keep the lettuce and spinach in pots in the coldframe until the space is needed for summer stuff. The mustard seedlings have already sent roots through the bottom of the cells. I’ll plant them and the chard in open spots.

Aside from lettuce, the odds of harvesting anything before Groundhogs’ Day are slim. Late February to March is more probable. By then, I’ll be focused on seedlings for summer. As always, I”ll keep you posted.

Happy Holidays!