Tomatoes are usually planted in the garden after the danger of frost has passed for your planting zone. Unfortunately, you can not always count on the weather to be consistent, so occasionally you may find that you have a "frost warning" after you have diligently moved your tomato plants to the garden. A frost is not merely freezing temperatures, but it is when those temperatures are accompanied by moisture and dew, and this dew lands on the tomato plants and freezes, which can kill the plant's cells. When you have a frost warning for your area, don't panic. You can easily protect your plants from harm.
Lay mulch, such as shredded newspaper or hay, on top of the soil at the bottom of the plant. This will help keep heat in the ground.
Cover the plant foliage with a bedroom sheet. If your plants are still relatively small, in the evening open a large paper bag and set it over the plant.
Remove the covering in the morning, after the air has begun to warm up.
Repeat the process in the evening if there is another frost predicted for your area.