Typically you won't worry about frost protection in spring because you know when to plant tomatoes by consulting charts. But what if you want to get an early crop?
You could try setting out your tomato transplants a month early; but, I'd advise you to first learn some methods and strategies to protect your young plants from cold weather. Don't forget to uncover plants on warm days to avoid overheating. Consider using one of the following ideas to protect your plants from frost.
Want to extend your growing season and don't have a greenhouse? You should consider using cold frames, which can be thought of as mini greenhouses. In fact, you may be able to grow vegetables for a garden salad 12 months a year if your climate isn't extremely cold. Leaf lettuce grows particularly well in cold frames. They're also great for hardening off seedlings. It's easy to build a cold frame yourself, and I show you how.
If you want a pre-made cold frame check out Burpee's cold frame. I haven't tested it myself but it looks pretty solid.
Plastic sheeting is commonly used to cover frames or cages used for frost protection. But an alternative to using clear plastic sheeting and frames is using floating spun-bonded fabric row covers.
Fabric row covers are lighter in weight than plastic and can protect your plants from insects as well as frost. They are light enough to be spread directly on top of plants and are manufactured in a variety of weights and opacity; heavier weight fabric provides better frost protection.
Row covers can also be used in cooler climates as protection against insects during the summer.
One source I know of is Gardener's Supply Company's All-Purpose Fabric which is available in different sizes.
Encircle your plant with a teepee of water. Wall-O-Waters (aka Season Starters) and Kozy Coats all use the same concept. Kozy Coats hold 3 gallons of water and are made of red plastic. The red color is reflected onto the plant, which has been shown to increase the fruit production of tomatoes. Manufacturers claim you can plant up to two months early using these devices. This will depend on your local conditions, of course.
HotKaps (or Hot Kaps) are small waxed paper tents that are used by commercial growers and home gardeners to provide a protected environment for plants. Keep your plants covered at most times except on warm, sunny spring days. On those days, temporarily uncover. They are manufactured in several sizes; for tomatoes, order the large size.
A substitute for HotKaps is large, brown paper bags.
An old-fashioned garden cloche is a bell-shaped glass jar which protects seedlings from frost. They have been used as far back as the 1700's. It is said that farms outside Paris could be seen using thousands of these in the fields in the 1800's. HotKaps are the modern substitute for these glass relics. Antique glass cloches still work, of course, and they also make great decorative garden ornaments.
Glass garden cloches are still manufactured. Gardener's Supply Co. carries glass cloches and also less expensive plastic Solar Bells. Another similar product, Ferry-Morse Seed Plastic Plant Cover is available through Amazon.com and has received good reviews.
Tomato automators (aka tomato trays) are black or red lightweight plastic trays that surround the base of the plant. The hollow downward cones at the four corners direct water and nutrients to the root zone. The plastic absorbs solar heat during the day to warm the soil.
I'm testing the black trays out this year. Another obvious benefit to the trays is blocking worms and weeds.
Using one or several of the above frost protection strategies can put produce on your table four to six weeks early!