Do you want your tomato vines to be healthy and productive all summer? It helps to prune them. Here’s how to do it:

Know which type of vine you are growing. This makes a big difference. Varieties with determinate vines are compact and require minimal pruning. They grow no more than 4 feet tall and set a concentrated harvest of fruits. Popular determinate varieties include ‘Celebrity’, ‘Mountain Fresh Plus’, ‘Roma’, ‘Sheyenne’, and bush types such as ‘Better Bush’ and ‘Patio’.

Varieties with indeterminate vines will grow robustly until frost. They require extensive pruning. Popular indeterminate varieties include ‘Beefmaster’, ‘Beefsteak’, ‘Better Boy’, ‘Big Beef’, ‘Big Boy’, ‘Early Girl’, ‘Jet Star’, ‘Juliet’, ‘Large Red Cherry’, ‘Red Grape’, ‘San Marzano’, ‘SunSugar’, ‘Supersonic’, ‘Supersweet 100’, ‘Yellow Pear’ and most heirlooms.

Remove the lower leaves.  After you trellis your vines, remove any leaves that touch the soil. These leaves become shaded, attract diseases from soil debris, and reduce air circulation in the planting.

Find one good sucker. Understand that each tomato leaf is a compound leaf, usually consisting of five to nine leaflets. Suckers form at the base of leaves (see drawing).

Find the first flower cluster. Below it is a sturdy sucker that can produce lots of fruits. Let’s call this Sucker One. We want to keep it.

Remove all suckers below Sucker One.

If you have a determinate variety, you are done pruning for the summer.

If you have an indeterminate variety, you need to remove the suckers above Sucker One as well. This will leave us with two stems: the main stem and Sucker One. Undesired suckers are removed every week or so. You can be less aggressive at removing the higher suckers if you feel your vines are thin.

Prune suckers when they are young and dry. Prune suckers when they are about 3 inches long. Larger suckers will create larger wounds. Snap suckers off using your fingers or cut them with a scissors or pruners. Prune suckers when vines are dry to prevent spreading diseases.

Trim back overgrown plants later this summer.  Trim back vines if they are growing over your trellis. 

Also, you can snip off the leaders of vines 30 days before frost is expected. This will channel the vine’s energy into ripening fruits rather than producing more leaves.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Drawing courtesy of Andrew Carbury, How to Prune Tomatoes, Wikihow, www.wikihow.com/PruneTomatoes.