Pruning Tomato Suckers: How to Do It Right

Contents

• What is a tomato sucker?
• Determinate or indeterminate: which plant do you have?
• How to prune tomato suckers step by step
• How often should you prune tomato suckers?
• One stem or two: how many should you keep?
• Pruning timetable for USDA zones 3–6
• Topping: the last cut before harvest
• Does removing suckers actually increase yield?
• Leaf removal, wounds and disease spread
• What to do with the suckers you remove
• Common mistakes
• Frequently asked questions

What is a tomato sucker?

A tomato sucker is a shoot that forms in the axil, the V-shaped notch where a leaf stalk joins the main stem. Left alone it becomes a full second stem with its own leaves, its own flower clusters and its own fruit.

The name is misleading. A sucker is not a parasite. Within two or three weeks of appearing it carries enough leaf area to produce more sugar than it consumes. Removing one is a deliberate trade for airflow, earlier ripening and a plant you can tie up — not a rescue operation.

Telling a sucker from a flower cluster

New growers hesitate for fear of pinching out the wrong thing. Three structures grow off the main stem, and they are easy to tell apart:

• The sucker sits inside the leaf axil, pointing up and out at roughly 45 degrees. It has tiny leaves from the moment it appears.
• The flower cluster (truss) emerges straight from the stem, between two leaf joints, never from an axil. It has no true leaves — just a branched stalk with buds or small yellow star-shaped flowers.
• The growing tip sits at the very top of the stem. Leave it alone until it is time to top the plant.

The rule: in the notch, with leaves, take it out. On the stem, with buds, leave it alone.

Why anyone bothers

• Airflow. An unpruned vine becomes a wall of leaves with dead air inside — the exact microclimate late blight, early blight and grey mould want. In a small tunnel in August this is the best reason of all.
• Earlier ripening. Fewer fruits, more light on each, faster colour. In zone 4, three weeks earlier is the difference between a bowl of tomatoes and a bucket of green ones.
• Manageability. One stem can be spiralled up a string. Six cannot.
• Fruit size. Fewer fruits per plant means each one gets a bigger share. Most visible on beefsteak types.

Determinate or indeterminate: which plant do you have?

This is where most pruning advice goes wrong, and it is the only part of this guide you cannot skip.

Indeterminate (vining, cordon)

These keep growing as long as light, warmth and food hold out; the growing tip never stops making new leaf pairs and trusses. Under glass in a cool climate they easily reach 2.5 m (8 ft). Most beefsteaks, most cherry tomatoes and nearly every heirloom belongs here.

Prune these. Remove every sucker, all season, all the way up — except for the stems you deliberately choose to keep.

Determinate (bush)

These have a built-in stop. Each stem ends in a flower cluster after a set number of trusses, and that is that. The whole plant flowers at roughly the same time and ripens over two or three weeks, usually topping out at 60–120 cm (2–4 ft). Paste and canning varieties are often determinate, which suits anyone putting up sauce in one weekend.

Do not prune these the way you prune a vine. Every sucker you remove is an entire branch of flower clusters that will never be replaced. Prune a determinate plant like an indeterminate one and you can lose half the crop.

One refinement almost nobody mentions comes from commercial stake-and-weave practice: on determinate plants it is worth removing the suckers below the first flower cluster. Those bottom shoots sit close to the soil, get poor light and are the main entry point for soil-splashed disease. The exception within the exception: the sucker immediately below the first cluster is unusually vigorous and carries a lot of fruit — keep that one. Do it as the first cluster starts to bloom, then stop.

Semi-determinate: the missing third category

A growing number of modern varieties sit between the two. They stop eventually, like a bush type, but reach 130–180 cm (4–6 ft) and spread the harvest over four to six weeks. Many greenhouse and container varieties behave this way, and the tag rarely says so.

Practical handling: treat them as a cautious vine. Keep two or three stems, remove the rest, and stop pruning once the tips finish in flower clusters instead of new leaves. The plant has made its decision and further leaf removal only costs you sugar.

How to tell when the label is gone

Look at the top when the plant reaches 50–60 cm (20–24 in). If the main stem ends in a flower cluster and growth carries on from a side shoot below it, you have a determinate or semi-determinate plant. If the stem runs straight on, alternating leaf pairs and trusses, it is indeterminate. A second tell: vining types set a truss every third leaf, very regularly.

Save yourself the guessing next spring by checking growth habit before you buy. Our rundown of best tomato varieties lists the habit for every variety for exactly this reason.

How to prune tomato suckers step by step

With a rhythm the whole job takes one to two minutes per plant.

1. Pick a dry morning. The wound needs to dry before evening. Pruning in rain or heavy dew leaves an open, wet cut for hours, which is precisely the opening grey mould needs to get into the stem.
2. Wash your hands. Tobacco mosaic virus survives in cured tobacco and moves from fingers to tomato plants. If you smoke, wash with soap and water first, and again after handling any suspect plant.
3. Confirm the growth habit. Indeterminate: work through the whole list. Determinate: apply steps 5–7 only to the shoots below the first flower cluster, keep the topmost of those, then skip to step 10.
4. Start at the bottom and work up. The lowest suckers are always biggest. Working bottom to top also means you scan the plant systematically instead of missing shoots on the far side.
5. Search the axils. Follow the main stem with your eyes. At every leaf joint, look into the notch between leaf stalk and stem. The sucker often hides under the leaf above — push that leaf aside with your other hand.
6. Snap shoots under 8 cm (3 in) with your fingers. Take the shoot between thumb and forefinger as close to the stem as you can reach. Bend it sideways, back and forth once, until it breaks off. Do not pull it straight out — a strip of bark comes with it and you end up with a long tear down the stem instead of a small round scar.
7. Cut shoots over 8 cm (3 in) with snips. Once a sucker turns woody, finger pressure crushes rather than snaps it. Use sharp, clean bypass snips and leave a 3–5 mm stub. Wipe the blades with 70 % alcohol between plants if disease is anywhere in the row.
8. Never remove more than a third of the foliage at once. If the plant turned into a thicket while you were away, split the work over two sessions a week apart. Stripping half the leaves at once stalls growth and exposes fruit to sunscald.
9. Clear the lowest leaves at the same time. Take everything off the bottom 20–30 cm (8–12 in) of stem, and thereafter any leaf below a cluster whose fruit has started to colour. Those leaves contribute almost nothing and act as a landing strip for soil-splashed spores.
10. Retie the new growth. With the suckers gone the stem is easy to twist round its string or clip to its stake. Do it now, while the top is still soft and flexible.
11. Carry the prunings out. Never drop cut shoots and leaves on the soil, especially under cover — they go mouldy within days. Compost them outside, or stand the best shoots in water to root them.
12. Set a reminder. Next round in seven to ten days. Regularity is the whole trick: a small shoot takes three seconds and a thumbnail, a big one takes snips and leaves a scar.

How often should you prune tomato suckers?

Every seven to ten days while the plant is growing hard. In a warm tunnel in July a sucker can go from invisible to 15 cm (6 in) in a week, so lean towards seven. In late May, with cool nights, every two weeks is plenty.

Attach the job to something you already do. If you hand-water three times a week, make the axil check part of that round — a quick scan while the can fills. It then never becomes a task you postpone.

When to start

The first pruning happens when the plant has four or five leaf pairs and the first side shoots are clearly recognisable, usually two to three weeks after transplanting. Earlier than that and suckers are hard to distinguish from developing flower buds.

Suckers rarely appear on seedlings kept cool and bright indoors. If they do show up on a plant still waiting in its pot, that is a sign it is root-bound and needs potting on or planting out. Timing for the indoor phase is covered in the guide on when to sow tomato seeds.

When to stop

Two to three weeks after topping. A topped plant pushes new shoots from the axils nearest the cut, trying to replace the lost growing tip. Let them run and the energy goes there instead of into the fruit. After a month the plant gives up and you can stop patrolling.

One stem or two: how many should you keep?

The stock answer of "one stem" is right for a greenhouse with string support and limited headroom. It is not the only right answer, though.

For a second stem, choose the strong sucker immediately below the first flower cluster and train it in its own direction — that shoot is reliably the most vigorous on the plant. Every other sucker comes off as usual, on both stems.

In containers, one stem is almost always right. Root volume, not light, sets the ceiling, and two stems in a 12 litre (3 gal) pot compete for the same water. Pot sizes and watering are covered in the guide on growing tomatoes in pots.

Pruning timetable for USDA zones 3–6

The rhythm of pruning is set by two dates: when the plant goes out, and when your season ends. The table below works back from average first fall frost in each zone, with topping six weeks before that date. Shift everything by a week either way depending on the year.

Two things follow. In zone 3 the window is so short that variety choice matters more than technique: an early cherry at 60 days finishes, a late beefsteak at 85 days does not. And a tunnel is worth roughly one zone at each end — start two weeks earlier, top two weeks later.

Topping: the last cut before harvest

Topping means cutting off the main growing tip — the same logic as sucker removal, applied once and for good: stop building, start ripening.

Count backwards from your first frost. A tomato needs roughly six weeks from pollinated flower to ripe fruit at the temperatures of late summer in zones 3–6. Any flower opening inside that window is wasted effort, and the sugar it would have used does more good in the clusters already set.

How to top

Cut the stem two leaf pairs above the highest cluster you intend to keep. Those two leaves feed that cluster. Cut immediately above the cluster instead and it ripens poorly and tastes thin.

Clusters to aim for in a cold climate: five to seven under cover, three to five outdoors. The Royal Horticultural Society gives seven and four respectively as its benchmark for cordon tomatoes, which lines up well with what a zone 5 or 6 season delivers. In zone 3 and 4, subtract one cluster.

After topping

Keep removing new side shoots for another two to three weeks. Strip leaves below ripening clusters so light reaches the fruit, but leave at least five or six full-size leaves — without them there is no sugar factory. Pinch off new flowers as they open.

One piece of folk advice you can safely ignore: severing roots or twisting the stem to "stress" the plant into ripening. There is no evidence it works, and it markedly raises the risk of split fruit the next time the plant gets a proper drink.

Does removing suckers actually increase yield?

Most pruning articles skip this, which is a shame — the trial data gives a far more interesting answer than "pruning improves your harvest".

An Oregon State University trial compared plants pruned to a single leader and staked against unpruned plants left to sprawl. The results did not flatter pruning across the board:

The conclusion is not to stop pruning. The conclusion is to know what you are buying. Pruning trades total weight for early ripening, bigger fruit and a plant you can manage. In zones 3 to 6 that trade is almost always worth making, because a plant that ripens three weeks earlier delivers more edible tomato than one carrying twice as much green fruit when the frost arrives.

If you garden in zone 6 with a long, warm September and plenty of space, letting a plant sprawl is a rational choice. Just plan on thick straw mulch, because whatever touches bare soil rots.

The other signal in the data is that cracking and blossom end rot both rise with pruning. A heavily pruned plant has less leaf mass to buffer water uptake, so every dry spell and heavy soak lands straight in the fruit. The fix is even watering, not less pruning.

Leaf removal, wounds and disease spread

Sucker removal and leaf removal go together but run on different schedules. Pruning suckers shapes the plant; removing leaves manages light and air around the fruit.

Which leaves to take

• Everything on the bottom 20–30 cm (8–12 in) of stem, as soon as the plant is established. These get splashed with soil at every watering and are the commonest way fungal disease gets aboard.
• Leaves below any cluster whose fruit has begun to colour. That cluster is finished being fed and the leaves now do more good gone.
• Yellow, spotted or wilted leaves, always and immediately, wherever they sit.

What not to remove: healthy green leaves above the highest colouring cluster. Those are the ones making sugar. A stripped plant with ten clusters ripens more slowly, not faster, and the fruit tastes flat.

The wounds

Every sucker leaves a small wound. A clean, fast-drying one heals in a day. A ragged tear from a thick shoot pulled straight out can stay open for a week. Hence the three rules: small shoots, dry weather, sideways snap.

Do not paint, seal or disinfect the cuts. Tomatoes heal best on their own in dry air. If you want to help, ventilate the greenhouse hard for the rest of the day.

Spread between plants

If one plant in a dozen has blight or mosaic virus, your hands and snips carry it down the row. Work through the healthy plants first and the suspect ones last, wipe blades with 70 % alcohol between plants, and wash up afterwards. The same discipline pays across the tunnel, since cucumbers share the space and some of the problems, as covered in the guide on how to grow cucumbers.

What to do with the suckers you remove

Do not bin them automatically. A tomato sucker is a ready-made cutting, and tomato stems root along their whole length, so they take easily.

Rooting in water

Take a shoot 10–15 cm (4–6 in) long, strip the lowest leaves and stand it in lukewarm water in bright light out of midday sun. Change the water every second day. White roots appear in seven to ten days. Pot it up, keep it moist for a week, done.

Rooting in soil

Faster, but needs more attention. Push the shoot 5 cm (2 in) into moist seed compost, keep it cool and shaded for three days, then bright and evenly moist. Roots in ten to fourteen days.

When it is too late

A rooted cutting needs ten to twelve weeks from rooting to first ripe fruit. The last useful rooting date column in the zone table works that back for you: around 10 June in zone 3, 25 July in zone 6. Later cuttings will not fruit outdoors, but they make excellent winter plants under a grow light and free insurance if a main plant is lost.

Rooted suckers also make good gifts — one taken in June is flowering by August. For the whole cycle from seed to harvest, see the guide on how to grow tomatoes.

Common mistakes

• Pruning a determinate plant like a vine. The most expensive error on this list. Every sucker removed from a bush variety is a branch carrying three or four clusters that will not be replaced. Check the growth habit before you start.
• Waiting until the suckers are big. A 25 cm (10 in) shoot leaves a wound the size of a thumbnail and has already spent three weeks of the plant's resources. A seven to ten day cycle prevents this entirely.
• Pulling the shoot straight out. A strip of bark peels away down the stem with it. Snap sideways instead, with one back-and-forth movement.
• Pruning in rain or late evening. Wet wounds are grey mould's best friend. Dry mornings only.
• Confusing a flower truss with a sucker. The truss comes off the stem between leaf joints and has no leaves. The sucker sits in the axil and always has leaves. Two extra seconds of looking solves it.
• Stripping too many leaves at once. More than a third of the foliage in one session stalls growth and exposes fruit to sunscald. Split the job.
• Forgetting to top. An untopped indeterminate plant spends all of August and September making flowers that will never become ripe tomatoes. Topping is the single highest-value cut of the season.
• Leaving prunings on the ground. Cut shoots and leaves go mouldy on the soil within days and become an infection source. Carry them out.

Frequently asked questions

Do you have to prune tomato suckers?
No plant dies for lack of pruning. But an unpruned indeterminate tomato becomes a dense, heavy thicket with still air inside and fruit that colours late. In zones 3 to 6, where the season ends in September or early October, that is often the difference between ripe tomatoes and green ones. Determinate varieties do perfectly well untouched.

How do I know if my tomato is determinate or indeterminate?
Check the top of the plant at 50–60 cm (20–24 in). If the main stem finishes in a flower cluster and a side shoot takes over growth, it is determinate. If the stem carries straight on, alternating leaf pairs and clusters, it is indeterminate. Seed catalogues almost always state the habit, even when the plant tag does not.

What size should a sucker be when I remove it?
Between 3 and 8 cm (1 and 3 in). At that size it is unmistakable, it snaps off cleanly between finger and thumb, and the wound dries within hours. Below 3 cm it is hard to distinguish from a developing flower bud. Above 8 cm the stem turns woody, you need snips, and the scar is bigger than it needs to be.

Can I accidentally remove a flower cluster?
It happens, and it is rarely serious — the plant sets more clusters higher up. Avoid it by checking where the shoot attaches. Flower clusters come directly off the main stem between two leaf joints and carry no leaves. Suckers sit in the notch between a leaf stalk and the stem and always carry small leaves.

Is it too late to prune tomatoes in August?
No. Keep taking suckers off until two to three weeks after you top the plant. Be more careful with leaves this late in the season, though: remove only leaves below clusters that have already started to colour, and leave at least five or six full-size leaves higher up so the fruit still gets sugar.

Can you plant tomato suckers?
Yes. A shoot 10–15 cm (4–6 in) long roots in a glass of water in seven to ten days, or in moist seed compost in ten to fourteen. To get fruit the same season, root it by about 10 June in zone 3, 25 June in zone 4, 10 July in zone 5 or 25 July in zone 6. Later cuttings make good indoor winter plants.

Should you prune cherry tomatoes?
Most cherry varieties are indeterminate and do benefit from pruning, but go gently. Keep two or three stems rather than one. The fruit is small and ripens fast, so you lose less by leaving extra leaf mass, and you gain a considerably longer picking season from a plant that keeps producing into autumn.

Why does my plant look thin and sparse after pruning?
You most likely took too much at once, or stripped leaves too high up the stem. A plant that loses more than a third of its foliage stalls for a couple of weeks. Let it recover, water evenly, give it one feed with a high-potassium fertiliser, and remove nothing else until fresh growth shows at the tip.

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