With a few exceptions, tomato varieties are almost all determinate or indeterminate, in the way they grow. Read on to learn how to prune them effectively for earlier, bigger, healthier tomatoes.
Determinate varieties have a determinate height, meaning that they grow to the specific height of that variety and don’t get any taller. The smallest determinate varieties are about 2’ tall, but the average is 3-4’. Fruit forms at the end of the branches of determinates. They produce plenty of fruit in a week or two, then are done for the season and die off. They also produce earlier. They are more manageable for beginner gardeners and those with short growing seasons or limited space. They also enable you go for a late summer vacation without worrying about care and harvesting.
Determinates grow suckers just like indeterminates. Suckers are the branches that form in the corner where the leaves meet the main stem. For best yield, pruning should be limited to only suckers below the first flower cluster and leaves that are in contact with the soil. The suckers produce more tomatoes without compromising the main stem and the plant stays bushy and compact.
Some varieties have stocky, sturdy main stems, but a cage is still recommended to protect against strong winds and heavy rain. Caged plants can benefit from leaf pruning. If it’s very dense in the center, removing or trimming leaves increases airflow. Good airflow helps prevent disease. Leaves nearest a fruit cluster are the ones that send sugar to that fruit, so when thinning, do not remove leaves directly above and below the cluster.
When growing indeterminates with determinates, consider a clear marking on the support, in case you auto-pilot and accidentally prune your determinates when you go out to remove suckers from all your plants.
Indeterminate varieties produce tomatoes all along the stems throughout the growing season, until they are killed by frost. Until the plant is about 12” tall, it uses all its energy to grow. Once it starts photosynthesizing more energy than the single growing tip can use, it will start to flower and sucker. Indeterminates can grow suckers endlessly; even after you remove them, more will emerge in their place. In general, more stems means more but smaller fruits, which are produced increasingly later in the season.
Left unpruned, a vigorous indeterminate tomato plant can easily cover a 5’ X 5’ area with as many as 10 stems, each as long as 5’.
This tangle of stems will be difficult to support above ground and makes the plant more susceptible to disease.
Staking and pruning helps to minimize disease and maximize photosynthesis, thus yielding earlier, larger, healthier fruit.
A properly pruned and supported single-stem tomato plant presents all its leaves to the sun to generate energy. Leaves that are shaded from the sun help to harbor disease and do little to feed the plant.
With only one growing tip to feed, most of the energy the plant produces goes to steadily developing fruit until frost. Also, by pruning the plant to a single stem you can grow more varieties in a small space. Pruned single stems can grow to over 6’, so be prepared with an accommodating support.
Only prune when the plant is dry to avoid disease affecting the wound. This should be done when the sucker is still small. Just snap it off – the small wound will heal quickly. Once a sucker becomes too big and tough, it needs to be cut, leaving a larger wound and increased risk of disease. When pruning, consider leaving a little stump of the sucker. The stump will eventually die back but it will buy you more time before a new sucker grows in its place.
Pruning also affects plant health. With fewer leaves, pruned plants are less dense, allowing more air to move through the plants. The leaves dry faster after a rain, so they are less susceptible to the diseases that need prolonged moisture to develop. Many tomato diseases, including septoria and early blight, can be present in soils. Soil splashes onto the plant is also reduced by pruning, minimizing bacterial and fungal pathogens that cause leaf spots and fruit rots. A more open and airy plant also make it easier to spot insect pests. As plants get taller, continue removing lower leaves up to 18 inches from the ground.
So far, we have covered simple pruning.
Missouri pruning reduces the shock of removing very large suckers on overgrown plants. This method involves removing the tip and most of each sucker but leaving a few leaves at the base. Also, since the wound is larger with a larger sucker, risk of disease is farther away from the main stem.
Leaf pruning
At planting, remove the lower leaves and bury plants either deep or horizontally in the soil. Leave about 3/4 of the plant above soil level. Tomatoes root all along the stem, so planting deeper will encourage them to develop more roots to feed the plant and fruit. Also consider removing any flowers present at planting time and up to when the plant is about 12” tall. This directs all its energy to go into root and leaf production, giving the plant a strong start to the growing season.
Tomato plants need lots of sunshine and air circulation to be healthy. For indeterminate tomatoes, all the leaves under the first fruit cluster are no longer needed and can be removed. Any leaf that is yellow or diseased does not help the plant and should be removed.
Taking leaves off also signals the plant to hasten reproduction; this means that it will speed up the ripening of fruit. Taking 2-4 leaves off every week, starting from the bottom as soon as fruit cluster develop, helps to have earlier ripe tomatoes.
Pruning fruit clusters. Sometimes tomato fruit clusters decide to grow into a leaf or branch; treat those as suckers and prune them off. Flower pruning and fruit pruning also causes the plant to focus on maturing and ripening the remaining fruit and flowers.
Topping your plants near the end of the season makes the difference between abundant dry, green fruit and fewer but juicer, riper fruit. About 30 days before the first frost, consider topping your plants to maximize ripening of existing fruit. Remove all the growing tips, flowers and tiny fruit. This will direct the plants energy to the existing fruit.