Photos: Ron Patterson | UI Horticulture Educator
There are three types of tomatoes based on growth habit: determinate, semi-determinate and indeterminate. In reality, there are only two growth types — determinate and indeterminate. The term “determinate” refers to what is happening at the end of the vine. Regardless of their growth habit, tomatoes tend to sprawl. Some sort of support or trellis system will help keep them contained in a smaller space while not adversely affecting yields. The more we can get tomatoes growing vertically, rather than sprawling, the more yield we can get per square foot of garden space.
Tomatoes have a main stem with alternate leaves at the nodes. At each leaf, there is a secondary stem, referred to in the industry as a sucker. Also along the branch and subsequent suckers, an average of every three nodes, there will be a flower cluster (truss). This basic anatomy determines how we train and support tomatoes to help save space in our gardens.
Determinate and semi-determinate
Determinate vines terminate with a flower truss when the vine reaches a certain length. There will be no more vegetative growth on that vine beyond the terminal flower truss. These plants are compact and typically produce a flush of fruit in a relatively short time, then they are done. Commercial growers like the condensed harvest window of determinate tomatoes.
Semi-determinate tomatoes are a taller determinate tomato. The vines still have a terminal flower truss, but the plants are taller and they have a longer harvest window. Many of the bush-type tomatoes grown for home production are considered semi-determinate.
The best support for determinate and semi-determinate tomatoes is either a cage or the “Florida weave” system. In eastern Idaho the cages with a narrow base tend to tip over with the wind and should be supported with a steel post. You can make your own wide-based cages from woven wire fencing or similar material. Use a material with holes large enough you can reach through to harvest.
Very little pruning needs to be done on determinate and semi-determinate tomatoes. They are easier to manage if the lower suckers are removed until the one just below the first flower truss. Beyond that, all suckers can stay on the stems. It is helpful to remove the interior leaves as they are not contributing to photosynthesis. This will reduce disease pressure inside the plant canopy.
Indeterminate vines almost always have a vegetative bud at the end (every now and then a vine may terminate with a flower truss). The vines will keep growing until something kills the plant. It is possible to have tomato vines up to 20 feet long in eastern Idaho. As you can imagine, these vines are difficult to manage with just a cage. A trellis can be a simple structure to support the growing vines. It also makes harvesting much easier.
Indeterminate tomato pruning is a little more complicated. Remove all suckers up to the one just below the first flower truss. Keep these two main stems and remove all other suckers, above and below those two stems. Along those two stems, about every third leaf, there will be another flower truss. Watch the video above about pruning and trellising indeterminate tomatoes.
Feel free to share your tomato patch space saving ideas in the comment section.
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