As the growing season shifts to winter mode, our attention turns to protecting food plants and flower beds and baskets for as long as possible. Watch for the first signs frost, which sneaks in on a clear windless autumn night. Fog or cloud cover tends to prevent a frost by trapping the heat that would otherwise escape skyward. Frost occurs when temperatures drop to just below freezing. Why all this frost watch diligence? Frost causes ice crystals to form in plant cells and thereby damages the cell walls. Leaves then shrivel and turn brown or black and the plant is doomed.
When the weather report suggests frost, protect plants by watering them thoroughly before sunset. Once the sun sets, much of the stored heat in the ground has dissipated. The soil will release moisture into the air around the plants throughout the night, keeping the air a couple of degrees warmer.
Another way to collect heat in the garden is to paint glass milk jugs black and fill them with water. Place them around any sensitive plants. The idea is that water loses heat at a slower rate than soil or air, so the collected heat will radiate outwards throughout the night, protecting the plants from frost.
To help slow the loss of heat rising from the plants and the ground, and to protect the moisture in the plant cells from freezing, build a simple frame around the plants and cover them before sunset using breathable material such as burlap, newspaper, cardboard, or even old bed sheets (avoid plastic which doesn’t allow moisture to escape), and secure with clothespins or giant binder clips. Uncover the plants in the morning to release any moisture and allow them to warm up. If the temperature stays low, leave the plant covered.
Or use commercial coverings designed to protect plants. These units may look more attractive than an old bed sheet, but a sheet does work just as well.
For smaller plants, make a mini greenhouse for each plant by cutting the bottoms off milk or soda jugs, removing the cap, and placing them over the plant. The plants stay warm and any condensation escapes through the top. Remove these in the morning. Alternatively, dig up the plants and move them indoors.
If possible, move container plants inside or into a greenhouse. They can also be covered and wrapped, with a layer of insulation such as burlap or bubble wrap around the pot to protect the roots. Or, bury the pot in the ground and cover the plant with newspaper or old sheets. At the very least, provide protection by moving them against the side of the house or shed.
Most plants respond well to being covered, but delicate foliage may not survive, even with the extra insulation. If plants succumb to a frost, leave the damaged parts intact as they will provide some insulation from further frost damage. The key is to be prepared.
Some vegetables such as leeks, beets, carrots, cabbage, kale, and broccoli are in no danger of frost. Even parsley, sage, and chives will survive. Accept the fact that frost is part of our natural cycle, and plan for next season.