Just in case there’s anyone reading this who doesn’t yet understand what a cold climate is (I’ve had Australian searchers looking for “hardy plants” arrive at this site), I thought I’d give an illustration. When I got up about an hour earlier, the outdoor temperature was 36 degrees F (that’s 2 degrees C for you Australians–and the rest of the world). Checking my electronic gadget’s memory, I learn that the low was 35.8 degrees F at 5:47am.
At dinner last night everyone was remarking on what perfect weather we had had that day, and how we could take a whole summer like it. I remember it being sunny with just a slight breeze, but I didn’t look at the thermometer. Fortunately another member of our family diligently checks the gadget’s memory each evening and records the highs and lows. That’s why I can tell you that the high yesterday was a toasty 67 degrees F (19 degrees C). (No, we don’t have a swimming pool–or central air conditioning.)
It doesn’t happen every year, but it’s happened enough years that we’re on our guard: frost the first week in June. Talitha, the chief vegetable gardener, had started planting the tomatoes (after all, a week ago it was in the high 80s and low 90s) in the ground, so they’ve been covered with a sheet the last two nights. The basil and peppers, as well as the hot weather annuals like zinnias, were still in pots and were brought into the house for these two questionable nights. Mind you, the weatherman hadn’t been predicting frost, just low 40s. But our own rule of thumb is to subtract ten degrees from what they predict for the low, especially if it’s a clear night and the temperature seems to be dropping fast.
These warm season crops can be stunted by soil or air temperatures that are too cold, even if they don’t get down to freezing. Tomatoes can be injured by temperatures below 50 degrees F. For basil, I think their growth is stunted below 60 degrees F, but I can’t find a website that comes right out and says that. The point is, frost will kill these warm-season crops, but unseasonably cool weather can be just as detrimental to their growth.
Of course, weather that’s too hot can cause blossom drop and other heat related injuries. The whole point of living here is so I don’t have to concern myself with heat related problems of any type–vegetable, animal, or mineral. I tend to feel mighty persecuted if the temperature goes above 90, especially if the humidity is high, which it almost invariably is. My thinking is, “I paid my dues last winter; this is a violation of some unspoken contract. I want my money back!” Sulking never seems to change the weather, but I keep trying.