Solving the mystery of the two main types of tomato plants
Indeterminate tomato varieties will grow ‘forever’. So they can grow over two seasons. Determinate varieties die after about 100 days. If you have a very short season to grow your tomato crop it is cheaper to buy a determinate variety, but if you want a long season and have ideal climate, get the indeterminate types.
The first shoot (or primary shoot) produces 5-10 leaves and a flower cluster. In indeterminate cultivars, the shoot continues to grow upward and flower clusters appear to develop to the side of main shoot or main stem. Most growers use indeterminate varieties in greenhouses as the main stem is allowed to grow several meters (10-20 feet). The lower leaves, which tend to look as if every disease possible is attacking them, are removed so that the bare stem is on the ground. Only the youngest healthy 1.8 m or 6-7 feet of leaves are left on the plant. In any case, these are the leaves that are actively contributing to the nutrition to the next harvest so the others are really not that necessary and only contribute as a safe haven for pests and diseases. All side shoots or suckers which grow out of the leaf axils are removed. Determinate varieties also have suckers but they are left on to grow. Note that the growth of the primary or first shoot ends in a fruit cluster with determinate varieties. The rest of the growth expansion is dependent on side shoot development (compared to indeterminate varieties where side shoots are removed).
So how do determinate varieties expand their growth? It is achieved by producing many side shoots on the main stem below the first flower cluster. Again three side shoots are produced and it ends in a flower cluster. The process repeats itself on and on until the plant dies after about 180 days or when frost kills the plant. Because there is a flower cluster on the main stem, it is much shorter and gives a bushy appearance. So the indeterminate plant can theoretically grow on forever since the main stem has a growth point at the tip while determinate varieties the growth point ends early on in a flower cluster.
The advantage of determinate varieties is that they produce fruit very early in the season as compared to indeterminate varieties. For that reason, seed companies have developed semi-determinate varieties focused on early yields, or put in another way, they peak early and yields taper off later in the season.
Processing tomatoes and fresh market tomatoes are determinate types. They grow lower to the ground, are easy to access. The short growth period or harvest period makes them ideal for outdoor planting as the next crop needs to be planted. If an indeterminate variety is used outside, it can often keep on growing until the low temperatures kill the plant. Yields are also very low at the end of the season due to low temperatures and not because the plant has reached the end of its life.