How to protect your garden from early frost | Gardening advice
THere are some dates on the gardening calendar that all gardeners should know about—and frost dates should be at the top of the list. No one can guess the exact date of the year’s last frost, but it’s important to know how to anticipate that first cold night and how it affects our plants. Knowing which of your plants can tolerate lower temperatures and which cannot is key to planning what to plant and when.
There are two main types of frost: air and ground. Air frost occurs when the air temperature drops to or below the freezing point of water (0°C or 32°F), while ground frost occurs when the ground temperature drops to this low level. They can occur separately, although they often occur together, and both can damage plants to varying degrees.
When water in plant cells is exposed to freezing temperatures, the cell walls can burst, damaging the plant and often causing it to turn black and die. Different plants have different levels of frost tolerance, ranging from tender (such as tomatoes) to hardy (such as evergreen trees, such as pines).
For many edible plants — from beans to summer lettuce and cucumbers — the first hard frost marks the end of their lives. However, I have been able to keep some crops tender for an additional two weeks with fleece protection or by moving container-grown plants – like my gooseberries, this season – to protected locations.
There are quite a few plants that can handle some freezing weather, including leeks, chard, some types of cabbage and kale – the latter two get sweeter in the winter as cold temperatures cause them to convert starch into sugar.
Interestingly, there are some areas that are more susceptible to freezing than others, known as frost pockets. Since cold air is denser than warm air, it tends to flow downward, which means that in a garden on a slope, for example, the bottom of the growing space will be more vulnerable to early and late frosts than a sheltered spot at a higher point. Avoid planting tender plants in a frost pocket, but if you do, be prepared to encase them even on moderately cold nights.
Predicting frost is a challenge even for meteorologists. They only forecast the air temperature, so remember that there could be frost even if the temperature does not drop to 0°C. A cold, clear, cloudless night is often preceded by a ground frost that is devastating to the plant.
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If you’re new to the garden, ask your neighbors (they better be the happiest plant owners!) if they know the dates of the first frosts for the past few years. From this year on, you should resolve to write down the date of the cold so you can factor it into your farming plans.