Answer: Once the main stem is horizontal, there is an increased tendency to branch. Left to its own devices, a vigorous indeterminate tomato plant can easily cover a 4- by 4-foot area with as many as 10 stems, each 3 to 5 feet long. By season's end, it will be an unsightly, impenetrable, disease-wracked tangle.
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.
Side stems affect plant vigor
As a tomato grows, side shoots, or suckers, form in the crotches, or axils, between the leaves and the main stem. If left alone, these suckers will grow just like the main stem, producing flowers and fruit.
Suckers appear sequentially, from the bottom of the plant up. The farther up on the plant a sucker develops, the weaker it is, because the sugar concentration gets lower as you move up the plant. On the other hand, side stems arising from below the first flower cluster, although stronger, compromise the strength of the main stem. For a multi-stemmed plant, your aim is to have all stems roughly the same size, although the main stem should always be stronger, because it has to feed the entire plant for the next five or six months. Here's how I achieve this.
I keep tomatoes free of side stems below the first fruit cluster. When trained to one vine and left free-standing, tomato plants develop strong main stems. To encourage a strong stem, I remove all suckers and I don't tie plants to their supports until the first flowers appear.
Determinate tomatoes need no pruning other than removing all suckers below the first flower cluster, because pruning won't affect their fruit size or plant vigor. If you do any pruning at all above the first flower cluster on determinate tomatoes, you'll only be throwing away potential fruit.
Indeterminate tomatoes can have from one to many stems, although four is the most I'd recommend. The fewer the stems, the fewer but larger the fruits, and the less room the plant needs in the garden. For a multi-stemmed plant, let a second stem grow from the first node above the first fruit. Allow a third stem to develop from the second node above the first set fruit, and so forth. Keeping the branching as close to the first fruit as possible means those side stems will be vigorous but will not overpower the main stem.
There are two ways to deal with a sucker that isn't destined to become a stem. The simplest is to pinch it off entirely; not surprisingly, this is called "simple pruning." This should be done when the sucker is still small and succulent. Grab the base of it between your thumb and index finger and bend it back and forth. The sucker should snap off, producing a small wound, which will heal quickly. Avoid cutting the sucker with a knife or scissors, because the resulting stump can become easily infected. Once a sucker becomes too tough and leathery to snap off, however, you'll have to use a blade. I recommend a retractable razor knife.
The second option is Missouri pruning. In Missouri pruning, you pinch out just the tip of the sucker, letting one or two leaves remain. The advantage is that the plant has more leaf area for photosynthesis and to protect developing fruit from sun-scald. The disadvantage is that new suckers inevitably develop along the side stems, adding to your future pruning chores.
Missouri pruning is necessary when things have gotten out of hand. When you're dealing with large suckers, it's better to pinch off just the tip than to cut off the whole thing close to the main stem. For one thing, if disease hits, it's farther away from the main stem. And for another, removing just the growing tip is less of a shock to the plant than removing a foot or so of side stem.
You'll find that suckers grow very quickly during the hot summer months. I can't count the times I've returned home from a five-day road trip in July to find my formerly well-tended tomatoes covered with foot-long suckers growing in all the wrong directions. This is indeed a situation that tests one's resolve. It helps to know that side stems started this late in the season will always be spindly and produce inferior fruit. You must be heartless and tip them all.
Hope this helps you control the jungle out there!
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