No matter how warm it is right now, we are in the beginning of the change to fall, with its eventual killing frost.
Even though our average first frost date is Sept. 15, we can get an early frost in late August. In 2008, we actually had frosts in the Spokane area every month of summer. It’s time to start thinking about protecting the late flowers and vegetables from that first blast of cold.
Understanding the microclimate in your garden is the first way to guard against being surprised by a frost. Observe where the frosts first damage plants. This will tell you where the cold air settles in your garden. Does your garden get a frost when the general forecast only said it was going to get down to the mid- to upper 30s? Is your garden one of the last to succumb to the frosts? Understanding this will help you plan.
For those one- or two-night sudden cold snaps, almost anything lightweight and flexible can be used to cover tender plants and capture ground heat. Tomatoes, peppers, melons, squash, beans, corn and cucumbers are the most sensitive to frost, so they will need protection long before crops like carrots, beets, potatoes and cabbage.
Plastic sheeting, cloth sheets, light tarps, even large sheets of cardboard can be used to cover plants in the evening before a predicted frost. These will have to be removed each morning before the sun gets warm enough to cook the plants.
To add more heat around plants, you can place five-gallon buckets of water, large timbers, rocks or pieces of concrete around sensitive plants to soak up daytime heat and radiate it back to the plants at night.
Another alternative is floating row cover. This lightweight, spun polyester fabric can be used to cover almost any garden crop and actually can be left in place until the last of the harvest. At night, the fabric can trap enough ground heat to keep the temperature under the cover as much as 2 to 5 degrees warmer than the outside air, more than enough to protect against light frosts. It is inexpensive, easy to handle, comes in several widths and lengths and can be reused for several years if handled properly.
Just as this fabric keeps the air around plants warm at night, it can also keep it warm during the day by as much as 10 degrees. This additional daytime heat can help ripen the crop it is protecting.
My garden often cools off enough in late August that it is hard to get tomatoes and other warm-season crops to ripen. After the August heat leaves, I cover the plants with floating row cover held up by a simple frame of PVC pipe and leave it there. The fabric is porous, so water, air and light can get through to the plants.