The ice storm that passed through Ontario late last week may have disrupted more than just your travel plans. If your power went out, and your generator didn’t kick on right away your greenhouse might have dipped in temperature overnight, leading to possible cold or chilling injury.Of course there was no physical frost, ice or snow in the greenhouse, but a sudden, dramatic shift in temperature can really throw your plants for a loop. It’s often not solely the low temperature that’s to blame, the amount of the temperature change and the speed at which the temperature changes are the factors that cause the most damage. As an example, a drop in temperature from 20°C to 5°C over 24 hours will cause less damage than that same drop over only 4 hours.
How can I recognize cold injury?
Chilling injury can present in many different ways. Commonly, damage can be seen on leaf edges and it progresses inwards. Affected tissue may look necrotic, purple or even bronzed. Leaves may appear curled or folded inwards. Leaf blotching or indenting can occur, especially if leaves happened to be wet. Symptoms can appear within 24 hours of the stress, or take several days to show up.
How do I care for my affected plants?
The first step is to restore your climate, and hopefully this was your initial concern (well before you noticed the plant damage!). Your best chance to save a crop is to minimize the length and amount of temperature change. Some plants will recover fully after removing the affected leaves. Plants that will recover should generally perk up and look more like themselves within a few days of fixing the problem.
For a good resource on cold injury during shipping of cuttings check out this article posted awhile back by the extension staff at Michigan State University. It’s got great pictures of some nasty chilling stress.