Mature Tomato plants, without support such as a trellis or cage tend to sprawl on the ground and collapse under the weight of a bounty of healthy tomatoes. On the ground they become much more susceptible to pathogens, fungal diseases, wilts and the ever present insects.
A properly supported and pruned tomato plant exposes the maximum surface area of its leaves to the sun, and will produce larger healthier tomatoes several weeks earlier than a prostrate one. Sugar produced by a properly pruned and supported tomato plant is directed to the developing fruit, not unnecessary foliage.
The leaves of a properly maintained plant dry off quicker, hence bacterial and fungal pathogens have less opportunity to spread. Soil is not as likely to splash up onto straight well supported upright plants. Basically upright tomato plants have fewer problems with leaf spots and fruit rots and greater production, both in quality and quantity. [Also See: Pruning Tomato Plants and Tomato Plant Diseases]
One of the simplest and most common methods to trellis tomatoes in the home garden is a tomato cage, which is just dandy if you only have a few plants. It becomes much more cumbersome as your garden expands, not to mention less cost effective.
One cost effective and efficient method is what is known as the Florida weave, or Cats Cradle. It works well with Tomatoes planted in a straight row and properly spaced at about 2 -3 feet apart. Drive stakes into the ground at the beginning and end of each row, in longer rows , a center stake or several additional takes is also advisable. In gardens subjected to heavy winds, sometimes every other plant may need a stake. Jute twine is best, it is strong, eco-friendly and biodegradable. At season end it can go directly into the compost pile .
When the plants have reached about a foot in height, weave twine from the primary tomato stems to the stakes to support them and prevent them from drooping to the soil level.
The twine should be fastened to the first stake about 6 inches above the soil level. Loop the twine around subsequent stakes, be sure to keep the line taut, or you'll be defeating the purpose as one drooping plant can drag the rest down.