With tomatoes, you want to maximize the efficiency of photosynthesis and minimize the risk of disease. This is best accomplished by ensuring that each leaf has plenty of room and is supported up off the ground. When a tomato plant lies on the ground, or when its growth is extremely dense, many of its leaves are forced into permanent shade, greatly reducing the amount of sugar they produce. If a leaf uses more sugar than it makes, eventually it will yellow and drop off. A pruned and staked plant will produce larger fruit two to three weeks earlier than a prostrate one.
A properly pruned and supported single-stem tomato plant presents all of its leaves to the sun. Most of the sugar produced is directed to the developing fruit, since the only competition is a single growing tip. The result is large fruits that are steadily produced until frost. If more stems are allowed to develop, some of the precious sugar production is diverted from fruit to multiple growing tips. Fruit production, although slowed, never stops. The result is a nearly continuous supply of fruits throughout the season. In general, more stems means more but smaller fruits, which are produced increasingly later in the season.
RULE 1 Get plants off the ground.
RULE 2 Give plants room.
RULE 3 Never prune or tie plants when the leaves are wet.
Pruning also affects plant health. The leaves of a pruned and supported plant dry off faster, so bacterial and fungal pathogens have less opportunity to spread. Soil is less liable to splash up onto staked plants. The bottom line: Upright plants have fewer problems with leaf spots and fruit rots because their leaves stay drier and free from pathogen-laden soil.
The way you choose to train and prune your tomato plants will affect how you space your plants, as well as the best method of support . There's no one right way to do it. Instead there are a few good patterns to follow.
Once flowering commences, all tomato vines must be tied to their supports. Although vigorous, the plants are also easily damaged, so take care in how you tie them and what you use. Cloth strips work well as long as they're not too old and threadbare. Pieces of panty hose cause the least damage to plants, but they're not biodegradable. Twine should be at least 1/8 inch thick, or else it can cut into the tomato stems.
There are two types of ties. Training ties direct plant growth upwards, and supporting ties keep it there. The top foot of a tomato stem, or leader, is very succulent and easily snapped; it needs to be directed upwards, gently. I would wrap a short piece of twine around the middle of the leader, cross it over on itself, and loosely tie it to the support. The resulting figure-eight tie reduces the chance the tender stem will rub against the support and get bruised.
Fruit will form along this stem. If left to the devices of the loose training ties, the weight of the fruit will pull the ties down the stake. Eventually, the stem will bend over and crease. Luckily, as the stem matures, it toughens; by the time fruit develops, the stem can tolerate a tighter tie. To support a fruit cluster as it fills and gains weight, I would loop a longer piece of twine, 12 to 18 inches, around the stem just above the fruit cluster, creating a sling. Then I would gently pull it up to take the weight off the stem. I would wrap the twine twice around the stake, and firmly tie it to the stake 6 to 10 inches higher than the point of attachment to the vine. To keep the tie from slipping, I would knot it underneath the point where the sling meets the stake.
Which method of support you use and how far apart you set tomato plants depends on the number of stems you allow to grow.
Cages work for plants with three to five stems. I would use them almost exclusively for determinate tomatoes. Ready-made tomato cages are too little for all but the smallest determinate cultivars. An ideal tomato cage is made from 5-foot-tall galvanized fencing with openings at least 4 inches square, so you can reach in and pick the fruit. A 4-foot section makes a cylinder about 15 inches in diameter. Secure it with baling wire, and stabilize it with two stakes, one of which is at least 6 feet long. Drive the stakes in within a week of planting, but wait to set cages over the plants until the first fruits form, to simplify weeding and pruning. Space caged plants about two-thirds of their final height in all directions.
Use the same type of fencing to make a tomato fence, which works best for plants with one or two stems. To get a good, solid fence, you need a helper. Secure the fencing with 6-foot stakes every 4 feet. Here's how I would keep the fence taut. Loop each non-end stake through the bottom rung of the fence, then start to drive it into the ground so its bottom is angled away from the previous stake. Once it's about 4 inches into the ground, bring the stake upright and drive it in the rest of the way. Set single-stemmed plants 18 inches apart, and double-stemmed plants 24 inches apart. If you stagger the planting (successive plants on opposite sides of the fence), you can knock 6 inches off these distances. Erect the fence before you plant your tomatoes.
Stakes work well for plants of one to four stems. I would use 1 inch x 1 inch x 6-foot lengths of untreated oak or cedar, sharpened on one end. Drive the stakes 8 to 12 inches into the ground, depending on your soil (deeper for loose, sandy ground). To avoid damaging roots, drive your stakes in within a week of planting. Space staked plants at 18 inches for a single stem, 24 inches for two stems, and 36 inches for three or four stems.
