Proper pruning will help you get the most out of your heirloom tomato plants. Pruning encourages heirloom tomato plants to grow larger, more flavorful tomatoes, produce more tomatoes throughout the season, escape disease and stay a more manageable size. Left unchecked many heirloom tomato plants can reach eight to ten feet in height with sprawling branches.
Pruning works by encouraging the tomato plant to focus its energy on developing tomatoes instead of on new leafy growth, resulting in larger, healthier and tastier tomatoes.
There are two main heirloom tomato varieties. If you have determinate heirloom tomato plants you probably won’t need to prune them. They will stay compact and produce a single large crop of tomatoes. Indeterminate heirloom tomato plants continue growing all season long. They constantly produce new stems, flowers and fruit and should be controlled with pruning.
REMEMBER: The growth tips of indeterminate heirloom tomato plants will not form blossoms. Tomatoes only form on the side shoots.
Objectives of Pruning Heirloom Tomato Plants
Pruning heirloom tomato plants is necessary to:
- Develop 1-4 strong main stems.
- Keep the heirloom tomato plants a manageable size.
- Keep leaves and stems from touching the ground.
- Allow light to reach the entire plant for good photosynthesis.
- Allow air to circulate to the center of the plant to deter mold, disease and pests.
How to Prune Heirloom Tomato Plants
While you can begin pruning any time after your heirloom tomato plants reach 12-18 inches in height, it is best to wait until they are strong and established.
Start out by allowing the first set of blossoms to grow. Remove all leaves and small stems below this cluster of blossoms.
Decide how many growing stems you want on your heirloom tomato plants. Single stemmed plants can be grown closely together, but they do not produce very much fruit. Most growers prefer 2-4 growing stems.
Image courtesy of bonnieplants.com
Creating Multiple Growing Stems on Heirloom Tomato Plants
Growing heirloom tomatoes with two stems:
Allow a growth tip or shoot to grow from the leaf axil (the first “V”) above the first blossom cluster.
Growing heirloom tomatoes with three stems:
Allow a growth tip to grow from the leaf axil directly above the second stem. Keep in mind that main growing stems should be close together to encourage strong, sturdy growth from the base of the plant.
Image courtesy of wattersgardencenter.com
Prune Side Shoots and Growing Tips
As your heirloom tomato plants grow they will continuously put out “suckers” or new growth tips. Allow these side shoots to grow at least two sets of leaves, and then pinch off the tip to stop further growth. The leaves will help protect fruit developing below from sunburn.
Limit Size
Once your heirloom tomato plants reach the size you want, pinch off all new growing tips. Eventually the plant will stop trying to grow up and focus on developing fruit below. As you continue to prune new growing tips it will begin to flower more heavily and set more fruit.
Prune Gently
Always err on the side of pruning lightly. Too much can put your heirloom tomato plants into shock, lowering their production and even killing them. A good rule of thumb is to never prune away more than 1/3 of the entire plant, even if it is overgrown or diseased. If you prune an old or overgrown plant heavily it will need a few weeks to recover. Don’t worry, it will begin to flower again!
Prune Heirloom Tomato Plants at the End of the Season
Four weeks before the first expected frost, prune away all new blossoms and suckers. This will encourage the plant to concentrate on the existing fruit, helping to ripen it before the frost.
Buying Heirloom Tomato Plants
Remember, you don’t have to start from seed. You can order heirloom tomato plants online or find healthy tomato plants for sale at your local farmer’s market in the springtime.
Extended Reading
The Guide to Growing and Eating Heirloom Tomatoes
Farmer Pete gives a lesson on pruning heirloom tomato plants: