Tomato plants do not like freezing temperatures. Gardeners can take a number of steps to protect their tomato plants from damage, no matter what type of tomatoes they are growing. If that is not possible, the damage may also be mitigated by other means. Which method a gardener chooses will depend largely upon personal preference, as well as available facilities and supplies.
Tomatoes of all kinds are considered tender annual plants. Unlike semi-hardy or hardy plants, this means they cannot tolerate any frost. From the biggest beefsteak to the tiniest yellow pear tomato, no tomato fares well when frost is in the forecast.
Tomato plants shrivel and discolor almost immediately once freezing temperatures occur. Fruits still on the plants change rapidly in flavor and texture, losing all the qualities that make people want to eat them. This process occurs whether or not tomatoes are ripe on their vines. Foliage may begin to drop off, and if flowers are still present, they will shrivel and drop off as well.
Mulch can help guard against sudden temperature changes for tomato plants. An application of 2 to 3 inches around each plant will help guard against mild frost. Mulch can be made of wood chips, straw, dead leaves, old newspapers or other organic matter available to the gardener. Mulch in conjunction with floating row covers, essentially big blankets made of lightweight material for plants, can work if the frost will only be temporary. You can then remove the row covers during the non-freezing hours of the day so the tomatoes can get vital sun. Cloches--like big stocking caps for plants--may be another option to consider.
If you are not concerned about further growth of tomato plants and merely want to ensure that existing tomatoes on the plants ripen, two options present themselves. You can uproot the affected tomato plants and bring them into a garage or basement to hang until the tomatoes ripen on the vine. You can also simply pick the green tomatoes and place them on a countertop inside the house, where they will ripen a bit more slowly.
Only consider transplanting tomato plants to pots to bring indoors if you have adequate space and a light source for the tomatoes. A window that gets full sun is optimal, but even in that case, sun is not as strong during the winter. Therefore, supplemental grow lights are necessary to extend the growing season indoors. If you do not have space or facilities, don't bring tomato plants indoors, as it will only lead to disappointment.