Paying attention to signs of frost extends season

By Kathy Hatfield
Gardening Columnist

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Cooler temperatures may be a welcome relief after an intensely hot summer, but they also signal that the growing season is on the downhill side. As we rush to gather as much as possible before conditions become too cool for ripening tomatoes and peppers, we need to be aware of the warning signals of impending frost and a sudden halt to the harvest.

Weather conditions can vary widely, depending on a garden's location. Even gardens within a short distance of each other can experience strikingly different weather. So when the weatherman predicts frost, it's important to pay attention to a few key signs of the likelihood that it will happen in your garden.

Garden location can be a major factor in determining the chances of a first fall frost. We all know that gardening at a higher elevation means a shorter growing season. And gardening at the top of a hill exposes the garden to chilling temperatures. But gardening on a low spot is not such a good idea either. Cold air is denser than warm air and settles in low spots. A garden at the bottom of a slope is more likely to suffer frost damage than one on a south-facing slope.

Soil fertility is linked to soil moisture. Fertile soils release more moisture into the air than nutrient-poor or sandy soils, which means plants growing in richer soil have a better chance of surviving an initial fall cold snap than those in thin or sandy soils.

Mulch is generally beneficial to garden plants, keeping warmth and moisture in the soil. And during those sweltering hot days we've experienced this summer, light-colored mulches help to keep the soil a bit cooler. But with impending frost, a mulched garden is more likely to suffer frost damage because this warmth is not released when needed.

Humidity is a plus in fending off frost. Just as evaporation requires heat, condensation releases heat. Our humidity is generally pretty low, but if there is sufficient moisture in the air from a recent rain or from watering the garden, it may be enough to protect your plants.

Clear skies with falling temperatures are usually an indication that frost is on the way. But if there are clouds in the sky, especially a low, thick cloud cover, the chances of frost are reduced. The clouds insulate the Earth like a blanket and trap the sun's heat. This may be enough to prevent frost from forming.

If there is little or no wind, the coldest air will settle to the ground and plants may freeze. A slight breeze could be enough to keep the cold air from settling and freezing your plants. Of course, a cold, blustery wind can harm plants too.

Pay attention to the weather forecast and note the dew point, the temperature at which the air is saturated with moisture. The higher the dew point, the less likely there will be frost. More moisture in the air means the temperature will be higher when the moisture starts to condense, so frost is less likely.

Some plants are more susceptible to frost damage than others based on their individual characteristics. For example, darker-leaved plants tend to absorb and store more heat, so will be less likely to be damaged by frost. Fuzzy-leaved plants trap a thin layer of air near the leaf surface that acts as insulation. Compact plants and those planted close together help to reduce the proportion of leaf damage from frost.

Once you've determined that frost is likely in your garden tonight, you have several options. If you're really not ready to say goodbye to the garden, you can cover your plants with almost anything that will retain a few degrees of heat. Place plastic tarps, pine boughs, newspapers, or bushel baskets over the plants before sundown to trap as much heat as possible. Anchor them well to prevent the wind carrying them away. Be sure to take the covers off as soon as the air temperature begins to warm.

Watering your garden the day frost is predicted can increase the humidity enough to protect plants. As the water evaporates from the soil, the humidity increases around the plants. Then as the air cools, moisture in the air condenses on the plants, releasing heat in the process.

The last option is to simply accept nature's timetable. Enjoy the break from garden chores, put up whatever produce you were able to harvest, and wait for next year's garden catalogs to arrive.