How to Prune Tomatoes: Removing Suckers, Tying In and Topping

One stem is the rule for large-fruited tomatoes

A beefsteak or slicing tomato only reaches full size if the plant concentrates on a small number of fruit. Grown on two or three stems, the way cherry tomatoes often are, you get more fruit but each one stays small. Grow a single main stem and remove every sucker, the shoot that appears in the angle between a leaf and the stem.

The one exception is a plant growing so vigorously that it is all leaf and no fruit. In that case leave a single sucker below the first truss and run it as a second stem, which gives the excess vigor somewhere to go. In a home garden this is not a common problem.

Take suckers off before they reach two inches

Suckers appear in the joint between a leaf and the main stem. While they are one to two inches (three to five cm) long you can pinch one between finger and thumb and bend it sideways, and it snaps off cleanly with a small wound. Once a sucker is four inches (ten cm) long the base has gone woody, you need pruners, and the cut is large enough to let disease in.

Do this on a dry morning. The wound dries during the day and seals itself. Suckers removed in the rain or in the evening stay damp all night, which is exactly how gray mold gets started.

1. Work from the bottom up Check every leaf joint from the base of the plant upwards. The ones you miss are almost always near the bottom.
2. Bend, do not pull Pinch the base of the sucker and push it sideways until it snaps. Pulling can tear a strip of skin off the main stem.
3. Use pruners on big ones For anything over four inches (ten cm), cut at the base with pruners and wipe the blades between plants. Leave the cut to dry.
4. Take the prunings away Do not drop suckers on the bed. They carry disease. You can also root them in water as spare plants.

There will be new suckers every single week. Leave it a fortnight and you have a second trunk, so pick a day of the week and stick to it.

Tie tightly to the stake and loosely to the stem

When you tie the plant in, wrap the twine firmly around the stake and loosely around the stem in a figure of eight. The stem thickens a great deal through summer, and a tie that grips it will cut in and choke off everything above that point.

Tie just below a truss. Once the fruit swells, that is where the weight hangs, so supporting it there stops the truss drooping and the stem snapping.

1. Tie below each truss Put a tie about two inches (five cm) below each flower truss. Do it while the flowers are open, not after the fruit has set.
2. Use a figure of eight Loop the twine round the stake, cross it over, then make a loose loop around the stem. You should be able to slip a finger between twine and stem.
3. Add a tie every week A tomato puts on eight to twelve inches (20 to 30 cm) a week in summer. Tie in the new growth on the same day you do the suckers.

How tall a stake do you need

Left alone a tomato will pass ten feet (three meters). With a stake of six or seven feet you are committing to stopping the plant after five or six trusses by pinching out the growing tip, which gardeners call topping. In other words the height of your stake decides how many trusses you can ripen.

A single upright stake per plant is the easiest to work with, and in a windy spot you can run a horizontal rail across the tops to tie them together. An A-frame is stronger but pushes the fruit into the middle of the row where it is awkward to pick, so for large tomatoes upright stakes are better.

Top the plant two leaves above the last truss

Once the plant reaches the top of its stake, count two leaves above the highest truss you intend to ripen and pinch out the tip there. Cutting immediately above the truss exposes the fruit to scorching sun and cuts off the flow of sugars, so the top tomatoes never fill out. The two leaves you leave behind feed that last truss.

Suckers keep coming after topping, so do not stop your weekly round. The sucker just below the top truss is especially vigorous and will take over as a new leader if you let it, stealing everything from the fruit you were trying to ripen.

1. Choose the final truss The last truss should be about a foot (30 cm) below the top of the stake. Anything above that will not ripen before the season ends.
2. Cut above two leaves Count two leaves above that truss and cut the main stem just below the third leaf, on a dry morning.

Strip the lower leaves to let air through

Once you have picked a truss, the leaves below it have no more work to do. Taking two or three of them off each time opens up the base of the plant, dries it faster after rain, and makes blight and gray mold much less likely.

Do not strip too much at once. Three leaves per visit is plenty, and never take leaves above the truss you are currently picking. Those upper leaves are the factory that fills out the remaining fruit, however untidy they look.

1. Work below the picked truss Find the truss you have finished picking and only take leaves below it. Leave everything above it alone.
2. Three leaves at a time Start with any that have yellowed, and snap them off sideways at the base. Removing green leaves wholesale weakens the plant.
3. Carry the leaves away Old lower leaves usually carry spores. Bag them rather than dropping them, or rain will splash the spores back up onto the plant.

Fixing pruning mistakes

A sucker you missed that has become a branch, a tie that has cut into the stem, topping the plant too early: all of these are recoverable. It is very rare for a pruning mistake to cost you the plant, so work through the symptoms one at a time.

1. A sucker has become a branch If it has no flowers, cut it off at the base. If it is carrying a truss, leave one leaf above that truss, pinch out the tip, and remove the branch after you have picked.
2. A tie has cut into the stem Cut the tie off and retie a little higher up. The scar stays but the flow of sugars recovers.
3. You snapped the growing tip Let the sucker just below the break grow on as the new leader. You lose a truss or two but picking continues.
4. The main stem ended in a flower That is a determinate habit and the stem will not extend. Train the nearest sucker below it as the new leader.