Growing tomatoes is a lot like some of the things we do in bonsai to balance energy in the plant.

As a tomato grows, axillary 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 and produce flowers/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 would be to have all stems roughly the same size, although the main stem should always be stronger, because it has to supply water & nutrients to the entire plant for the next several months.

A 'how to':

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, remove all suckers and 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 (until late in the year when you are sure frost will take the fruit before it can ripen on the stems you'll be pinching. I hope that made sense.).

Indeterminate tomatoes can have many stems. The fewer the stems, the fewer but larger the fruits, and the less room the plant takes up in a container. 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.

Al

"...and don't tie plants to their supports until the first flowers appear"

Al,
why not tie to supports until the first flowers appear. I can't say I've really paid attention to when I first loosely put some Velcro tape to the cage around the stem, but I imagine it's sometime around first flowering (they are usually not big enough to need it until about then)m but it's not because I was doing it deliberately. Wondering what the rationale is. TIA

Being able to move freely in the wind while stems are thin stimulates lignin production & strengthens stems. This is the same reason we try to avoid staking sapling trees if we can.

Al

Ah. That definitely needs to happen. Why first flower as the milestone? Is that just an easy thing to mark in time? Or does something change about the plant's development at that time?

Pruning everything below the first flower cluster promotes the development of a strong central stem. Some prefer to leave a couple of suckers on the lower portion of the plant, because these too, can be easily supported with staking. Then they prune the suckers from the remaining top growth of the plant, to prevent it from becoming too top heavy and falling or splitting.

Pruning tomato suckers reduces competition for nutrients with the original plant. You may eventually be setting more fruits if you leave the suckers grow, but the fruits will be smaller and the plant will be more cumbersome. Pruning tomato suckers is really just thinning the plants.

Pruning is never actually required and many gardeners donÂt bother with tomato pruning at all. The technique is as much trial and error as it is precision, so look at it as an experiment. When you first start pruning, do less rather than more. If you end up growing the same varieties year after year, youÂll get a feel for how they respond to pruning.

Al

Al, not sure we understood each other. I was asking about staking at first flowering, not pruning, a continuation of the question I'd asked earlier and you'd answered. Why use that milestone (or first flowers) instead of some other one? Does something happen within the plant at that time? Or is is simply a good milestone to remember that happens about the time that plant is large enough or has developed enough strength?

.... that happens about the time that plant is large enough or has developed enough strength.

.... and it's easier to put the cages on when they're not 3' and well along the path to behemoth stage. ;o)

Al