A few days before our average first day of frost (Oct. 9) I noticed some leaves on my climbing zucchini had been blackened by frost, although frost had not yet been forecast. The frost apparently descended in a narrow shaft of cold air, because the frost damage was not sufficiently extensive to kill the plant, or even damage some of the baseball bat-sized squashes hanging on the trellis.
Most of my very exposed garden was undamaged, although friends on the first bench and in the North End reported birdbath water was frozen solid. Fruits and vegetables produced by flowers are easily damaged by frost, and a frost kiss for just five minutes can leave damage. Leafy vegetables and root vegetables can tolerate frosts and some can even withstand freezes. Any food crops that have been frozen and thawed, or even brushed by frost and are damaged must be used quickly, others discarded.
How can you tell if food crops have been hit by frost? Watch for spots that appear water-soaked on pumpkins or squash. They should be used quickly, because most will spoil quickly. Some squash and gourds may harden, but I wouldn’t depend on it. If broccoli’s hit, the newest buds in the center of the head are most vulnerable. They’ll turn brown and emit a strong odor when thawed. Cauliflower curds also turn brown and yield stench when frosted and thawed. Cabbage leaves look somewhat translucent, and water-soaked, then turn limp when thawed. Blistered dead cells on outer leaves of lettuce turn tan, and begin to decay. Celery petioles (stalks) freeze more easily than the leaves, but both wilt and look like water soak when thawed.
Tomatoes develop watery soft spots from frost, and green fruits show a distinct color margin between healthy and damaged tissue. Pepper tissues look water soaked, and may be pitted or shriveled before they start to decay.
Freezing on root crops is harder to detect. Potatoes that have been frozen turn soft and watery after thawing, and show gray or blue-gray areas under the skin. Sweet potatoes show a yellow-green water-soaked appearance of interior and exterior tissues, the ring of material between those tissues showing yellow-green discoloration. Roots then soften and decay. Onions are water-soaked rings, visible when cut into cross slices, some of the scales appearing normal. Radishes may appear to be clear, just before they soften and shrivel. Carrots have a blistered appearance, and long cracks on the root. The interior looks dark and watery after it’s thawed.
To prevent damage, you can cover crops with plastic such as Visqueen, making sure the plastic is elevated above plants, for wherever they touch plastic, it will conduct cold and frost the plant. Floating row cover is more of a warmth blanket to an extent. Dead air space is also an excellent insulator, the main protection used by Maine gardener Eliot Coleman who gets a hardy crop well started, then installs row cover over it, and then rolls a large hoop house over the covered rows. That means there’s air insulation under the row cover, and a much larger air insulation between the covered row and the hoop house. The combination allows him to raise farmers market produce well into his cold winters.
Send garden questions to firstname.lastname@example.org or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.
Taking a break ...
Seed catalogs will be arriving soon to soften the harshness of biting cold, so I’m going to take some time off from writing weekly columns. Best wishes for peaceful happy holidays. I will continue to answer questions during this hiatus.