Prune Determinate Tomatoes

I have recently received a number of calls from growers about how to prune determinate tomatoes in a stake and weave system. Although this is relatively easy compared to how to prune indeterminate tomatoes with a trellis system, there are a few things I would like to call to your attention.

What to prune 

The common practice is to prune the suckers at the bottom of tomato plants. The benefit of this practice is to improve airflow which may help to control foliar diseases. Shoots of determinate tomatoes stop growing once they set a terminal bud. Most of us understand that if suckers are pruned too much, plants may have reduced yield.  However, there is confusion about exactly what to prune.

Normally, the bottom 6-7 suckers should be pruned until the first flower cluster. But it is important to note that the sucker just below the first flower cluster develops a very strong shoot (Figure 1), which will produce a large number of tomatoes. We find it works best to leave this sucker and prune everything below this point (Figure 2).

Figure 1. Leave the sucker right below the first flower cluster (indicated by the arrow on the right), prune this sucker (indicated by the arrow on the left) and all the other suckers below it.

Figure 1. Leave the sucker right below the first flower cluster (indicated by the arrow on the right), prune the sucker indicated by the arrow on the left, and all the suckers below it.

Figure 2. A tomato plant that has been pruned.

Figure 2. A tomato plant that has been pruned. Sometimes it works better to prune suckers first and prune bottom leaves when they begin to decline.

When to prune 

The ideal time to prune suckers is about when the first flower cluster start to bloom, around the stage showing in Figure 3. If suckers are pruned before the formation of the first flower cluster, it is difficult to know exactly what to prune. While if plants are pruned too late until the suckers grow big, removing suckers will create large lesions on the stem that facilitate the infection of pathogens. Another important consideration is that it is best for the lesions to dry out as soon as possible so there is less chance of disease infection. With this in mind, the morning of a sunny day normally is the best time to prune the plants.

Figure 2. Prune the suckers when the first flower cluster bloom.

Figure 3. Prune the suckers when the first flower cluster starts to bloom.


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