A few weeks ago, during our March heatwave, I seeded the first of our two cold frames with a mix of spring veggies: Bright Lights Swiss chard, Green Banner onions, Belle radishes, Viking spinach and an heirloom leaf lettuce mix.
The first to appear was the radishes, followed by about 50% of the lettuce. The chard and spinach were next, but the onions were pretty spotty.
Then a week later, on the first day of spring, the kids and I seeded the second cold frame with three more rows of mixed leaf lettuce, Polar spinach, Sparkler Tip radishes, a half row of Tennis Ball lettuce (2010) and a half of Buttercrunch lettuce (2010) and some red cored carrots, just for fun.
Then a few days later our 26 degree Celsius day unexpectedly plunged to a minus 8 degree Celsius night. The radishes in the first frame got killed off and the spinach tips and the sprouts on the out edges were damaged by frost, too. The second frame is faring better as the sprouts had yet to emerge at the time of this wickedly cold night.
I've noticed that the interior temperature of the frames vacillates between quite warm during the day (despite propping open the lids) and chilly at night, which is causing some stress on the more tender seedlings (not so much the spinach -- it's doing just fine).
The lettuce is ok, but small. No fresh greens for us this Easter weekend.
As this is our first early spring using the cold frames (we built them last year in late March, but didn't start seeding until April) it was a good reminder that because the boxes sit on top of the ground (not buried) I need to better insulate the outside of the frames with straw bales to buffer against these wacky temperature swings. I think adding a layer of insulation inside -- perhaps from a feed bag and/or a light layer of mulch -- would also provide some extra protection.
So it'll be a few weeks still before we're enjoying our greens but one thing I've learned is that growing food teaches patience, respect for Mother Nature's mood swings -- and perseverance!