Frost is a danger for outdoor garden plants as it gets cold. In some regions of the United States, early frosts can occur even in September. A frost occurs, usually at night, where the temperature dips below the freezing point. Tomatoes and other outdoor plants can by damaged by a frost.
Save your tomatoes from a frost by covering them in the evenings. As the fall approaches, toward the end of August, begin to pay attention to the weather reports. If you read your daily paper or watch your nightly news, you'll hear information about when a frost is possible. If you believe that it is going to frost, cover your tomatoes before the sun goes down.
You can use different methods for covering your tomatoes. Smaller plants can be covered by buckets or overturned pots. Larger plants can be covered by sheets. The covering will not prevent the tomatoes from being exposed to the temperatures. However, they will prevent the actual frost from touching the tomatoes, which is what will kill the plants.
If you know that you are heading into a period of many frosts, and you still have green tomatoes, think about harvesting them as is, or moving the plants indoors as possible.
After a Frost
Attempt to save your tomato plants after a frost. If you did not cover your tomatoes and they were exposed to a frost, you have several options. Depending on the severity of the frost, it might have only touched a few branches of leaves of your plant. Whatever has been touched by the frost will die within a few days. Pull off frozen or dead leaves as soon as you notice them. Some tomato plants might survive a quick or very light frost.
If the frost lasted for more than a few minutes, and dipped below freezing, your uncovered tomato plants will not survive. There is nothing you can do to save the actual plant. In a couple of days, it will wilt and die. At that time, it will stop providing nutrients to the tomatoes on the vine.
However, you can save some of the fruit. Anything that was green on the vine when the frost occurred will not be harmed. If the tomato plant has survived, or partially survived, it should be able to provide the green tomatoes with nutrients to become ripe. You can choose to wait and see if the plant has survived, or you can choose to harvest green tomatoes and use them in green tomato pie, or fried green tomatoes. Any red tomatoes on the vine will have been frozen and will not be able to be saved. However, the tomato can be immediately harvested and used in things like ketchup, salsa, or other tomato products that require the tomato to be mashed up.