Looking on the positive side, our recent end-of-April cold and snow remind us that April is a transition month, and May is the main planting month. Old-timers had it right when they cautioned not to be fooled by a few April warm spells.
In late April most gardeners haven’t planted tender annual flowers, tomato plants or other plants easily killed when temperatures drop below 32 degrees. But by the end of April perennials are usually peeking through the soil, tulips might be blooming, and trees and shrubs are beginning to show life. What effect will the cold have on them?
Luckily, perennial flowers, trees and shrubs are well-hardened in spring because they’ve grown through cold soil and experienced nights in the 30’s. They’re tough, and temperatures can drop down to 28-32 degrees with little or no noticeable damage to leaves or developing growth. The foliage of tulips and other spring bulbs is similarly hardy.
Even temperatures in the 25 to 28 degree range usually won’t harm perennials, trees and shrubs. But when temps drop to the low 20’s or below, that’s when newly-emerging foliage can be blackened from cold damage. If a gardener were inclined to cover valuable perennials, it might be a good idea if temps were forecast below 25 degrees.
The flowers of perennials and fruit trees are more frost-tender than the foliage. Research has shown that apple blossoms can tolerate temperatures down to about 25 degrees and still produce fruit. The borderline is 25 degrees. Below that, blossoms are usually damaged.
Tulips, daffodils, hyacinths and other spring flowers that are in full bloom when cold hits often turn dark and limp. They’ll usually tolerate 30-32 degrees ok, but temps in the 20’s are a problem.
Oddly enough, late spring snow that accompanies freezing temps can be a benefit. Dry cold is much more harmful than cold that’s accompanied by wet snow and moisture. Snow is a great insulator, and moisture-laden plants suffer much less damage than dry plants exposed to cold. Citrus growers down South use this concept to their advantage when they turn irrigation sprinklers on when frost is forecast. The citrus trees might be ice-covered by morning, but foliage is protected under the ice coat.