Determinate and indeterminate are two terms you’ll often see applied to tomato plants (Solanum lycopersicum) and they cause a bit of confusion with beginning gardeners… and even some fairly advanced ones. The two terms refer to how the plant grows and, indirectly, to the eventual size of the plant. Here’s my explanation:
The main stem of a determinate tomato ends in a cluster of flower buds and its secondary branches also end in flower buds. As a result, it stops growing in height fairly early in the season. The exact height does vary according to the cultivar, but determinate tomatoes remain quite compact plants and don’t really need much in the way of staking. The entire plant tends to flower nearly all at once and, as a result, the fruits all ripen at about the same time. These are the tomatoes you see growing in commercial fields: the fact that there are no stakes to worry about and that the fruits mature all at once means they are easily harvested by machine. For gardeners into canning and preserves, their “all ready at once” characteristic is also ideal.
Determinate tomatoes also tend to be earlier than indeterminate tomatoes and therefore good choices for climates with short growing seasons. The down side is that they produce fewer tomatoes than would a similar indeterminate tomato.
Indeterminate tomatoes have totally different growth habit. The tip of the stem doesn’t end in flower buds, but continues to grow upward. Flowers are instead produced on side branches. They are climbing plants and will need good staking. It’s not unusual to see indeterminate tomatoes, like the very popular ‘Sweet 100’ reach 8 feet (2,5 m) or more in height, even in temperate climates, only stopping when frost cuts them down. And in tropical climates, the sky is the limit. The tallest indeterminate tomato ever reached 19.8 m in height: that’s 65 feet!
Indeterminate tomatoes produce many more fruits than determinate tomatoes of similar types, often 3 or 4 times more, but do so over a long period, a few here and a few there, not all at once. Plus, they’re later to come to maturity than determinate tomatoes. They’re especially interesting when you like cooking with fresh tomatoes, as you’ll have fresh fruit continuously over a very long season.
Indeterminate tomatoes are the ones on which work-obsessed gardeners spend hours pruning off the so-called suckers. And if you do use the traditional 1 stake per plant staking method, you may have to do just that: it would be very difficult to fix all those branches to a single stake. When growing indeterminate tomatoes, though, you can avoid all that effort. Just use large tomato cages and simply push any wayward branches back inside the cage, so no pruning is required. That way, you get a much bigger yield, as those “suckers” are really branches and will produce tomatoes if you let them.
There are also semi-determinate tomatoes: taller than determinate tomatoes, but with a similar habit. However, not so tall you need a ladder to harvest them.
Please note that tomato growth habit does not affect fruit size, taste or color. You can find cherry tomatoes, slicing tomatoes, paste tomatoes, yellow tomatoes, pink tomatoes, etc. in all three groups.
As a gardener, I like to grow an especially early determinate tomato or two for an early harvest, but really bank on the indeterminates to supply most of my crop, offering me ripe tomatoes I can bite into until well into autumn.
Most tomato seed packets are clearly labeled determinate or indeterminate. If you buy tomato plants, though, you’re often given nothing more than a cultivar name, if that. You’ll have to ask the vendor what type it is!