Difference Between Determinant & Indeterminate Tomato Plants

To be, or not to be a determinate or indeterminate tomato plant, is not part of a gardeners decision making once the seeds are in hand. These traits are inherent in the tomato plants genetic imprint within the seed.

With either an indeterminate or determinate, tomato plant, 5 to 10 leaf fronds emerge out of the primary shoot of a young tomato vine before a flower cluster emerges. That means there will be at least 4 to 9 inter-nodes before a flower cluster appears on the vine. At that point the two types part company, so to speak. The indeterminate will keep growing in an exponential manner while the determinate will stop growing, get fatter stems and start focus on it’s fruits.

If a tomato reaches a certain size and stops growing, it is called a determinant tomato plant. However if the suckers keep on growing and growing out of the pot and into the frying pan, it is called indeterminate. The determinants stop growing and producing. The indeterminate’s keep on keeping on… forever, it seams. An indeterminate tomato plant will need to be pruned while a determinant will not. You can catch up on how to prune indeterminate suckers by reading Sucker Pruning a Tomato Plant. It’s easy to do!

Indeterminate Tomato Plants

Although indeterminate tomato plants look like they have a single main stem, this is not the case, all side shoots are replicates of the first stem. The growth of the first emerging stem ends with the formation of the first flower. Upward growth continues because the last leaf initiated before the flower cluster, produces a side shoot. These should be viewed as more main stems. The side shoot produces 3 more leaves before it produces another flower cluster. This process of initiating new growth from a side shoot of the last leaf (initiated before the flower cluster) continues indefinitely. This gives the appearance of another main stem with a flower cluster in the inter node between every three leaf nodes. Most heritage types are indeterminate varieties.

You can tell if a tomato plant is determinate or indeterminate by looking at how the flower cluster comes off the stem. If it is centered and shooting out from the tip of the stem, then it is a determinate plant. If the flower cluster is off to one side with the stem growing past the cluster, then it has an indeterminate growth pattern.

Determinant Tomato Plants

With a determinate tomato plant type, the process differs in that the side shoot above the first flower cluster produces 0 to 2 leaf nodes and a flower cluster but no further shoots. This ends the upward growth of the plant, making the main stem much shorter. Many side shoots will be sent from the first primary shoot. This gives the plant a bushy appearance. Each secondary side shoot eventually terminates in a flower cluster as did the primary shoot. Most determinate tomato plants need no support or pruning. The simultaneous growth of many flower clusters on determinate vines promotes earliness and concentrates fruit maturity compared to an indeterminate. Most modern commercial canners are determinate. It is the only way a commercial operation can function in a controlled growth environment. It is less work and fiddling in the garden or patio.

Semi-Determinant Tomato Plants

Few might want a 3rd class of a tomato plant but for clarities sake lets through it in. Shoots of semi-determinate plants produce several flower clusters to the side of an apparent main stem, like indeterminate’s, but eventually the shoot terminates in a flower cluster, as in determinate plants.

Most determinate varieties are recent hybrids. That is why almost all heirlooms are indeterminate tomato plants.