Most perennial plants and trees and shrubs are genetically wired to respond to warming temperatures. When a trend of ever-increasing daily temperatures is registered, it usually means that spring has arrived. That means it's time to wake up, time to open up the sleeping buds, time to sprout forth green growth. Plants react to the changes with no reference to a calendar.
When the warming trend is a fluke, the plant can suffer. Recently I enjoyed a week-long period of temperatures more than 20F degrees above average. December should give me days in the 40s (4C). Instead I enjoyed days in the 60s (16C). This winter has been relatively mild and many sections of my lawn are still green, even under the snow. With this trend of unusual warmth it's important to remember the rest of my landscape.
While it's not unusual for some non-evergreen perennial plants to have evergreen parts, my daisies have kept more green leaves at their core than I remember in recent years. They're ready to grow.
When I take a close look at my young fruit trees, it appears that some of the buds are beginning to swell, a sign that maybe they are receiving extra energy from the tree in anticipation of leaf growth. On some of the branches some buds already sprouted little leaves. The tree is confused, "thinking" that spring has arrived.
We can put on another layer of clothes and a warmer jacket. Plants have no such recourse. The tiny hope of new leaves on my apple tree will succumb to the cold. If not tonight when the low temperature is expected to drop near 0F (-18C), then soon when the lows will probably sink lower than that.
Daisy leaves can handle temperatures well below freezing, but if they're is exposed to historical lows in my area that can still hit -30F (-34C), they'll suffer.
Freezing temperatures below what a plant is designed to handle will kill new growth. The Daisy leaves won't survive to provide life-sustaining nutrients when the plant is ready to send up flower stalks. My herbs will shrivel. The awakened apple tree buds won't grow into strong new branches or tasty fruit.
The entire plant may not be killed in these conditions, but it can be damaged. Bushes and shrubs won't produce as many branches or flowers. Trees may lose the important buds that control their central trunk growth, resulting in new branch forks and ultimately reduced strength. Perennials can be stunted with less foliage and fewer flowers during the prime growing season. Fruit canes and trees may not bear at all.
There are a few things you can do if you're encountering the same conditions as I. Just as we appreciate a warm coat on a cold night, some plants can be saved by giving them a blanket. If you have new growth on a low-lying plant and are expecting frigid weather, cover it with a wool blanket or a tarp during the day before the low temperatures hit; you may be able to trap enough heat to give it a fighting chance. Surround and cover plants with a thick layer of straw. If you're lucky enough to have snow, leave it in place around your plants. Snow will keep the temperature near the freezing point, but that may be well above the colder air temperatures that can kill new growth.
Much of the time all we can do is react to the harsh reality of drastic temperature swings. Severe pruning may be necessary to eliminate dead branches. Entire plants may die and need to be replaced. Low crop yield shouldn't be a surprise.
It's difficult watching the inevitable decline, damage, or death of a plant. I wonder what effect today's cold will have on tomorrow's growth. Having no control over the situation is uncomfortable for a gardener.
All gardener's in cold regions have and will experience this problem, probably more-so in the future. Knowing that others are going through the same dilemma may be slightly helpful, but certainly not comforting.