How to Grow Tomatoes: Water, Feed and Pinch Out

Tomatoes are the crop most people try first and the one where small mistakes show up most visibly. Almost every tomato problem I have had, and every one I get asked about, traces back to one of three things: irregular watering, feeding at the wrong time, or not knowing whether the plant needed pinching out. Get those three right and the rest is picking.

The short answer

Find out whether your variety is cordon or bush, because cordons need a support and weekly pinching out and bush types need neither. Water consistently rather than heavily, since splitting and blossom end rot are both watering-consistency problems. Start a high potassium feed only once the first fruit has set. Thirty to forty litres minimum in a container. In warm wet weather watch for blight, which kills a plant in a week and has no cure.

Cordon or bush: check before you plant#

This single fact changes how you grow the plant, and the packet tells you.

Cordon, indeterminate, vine

One tall stem, up to two metres. Needs a cane or string support. Side shoots pinched out weekly. Fruits steadily over months. Most greenhouse varieties.

Bush, determinate

Low and spreading. No pinching, often no staking. Fruits in a shorter concentrated burst. Suits containers and hanging baskets.

Semi-determinate

In between, and treat it as a bush. Some support helps, pinching does not.

Pinching out a bush variety is the classic error, because you remove the shoots that were going to carry the crop. If the packet is lost and the plant is sprawling sideways rather than upwards, treat it as a bush.

Sowing and planting out#

Sow indoors six to eight weeks before your last frost date. Any earlier and the plants get leggy on a windowsill before it is safe to put them out.

Two seeds per small pot, thin to the strongest. Keep them at around 18 to 21C to germinate, then somewhere as bright as possible. Leggy pale seedlings are short of light, not warmth.

Pot on into a larger pot once the first true leaves are established. Tomatoes can be planted deeper than they were growing, and they will root from the buried stem, which makes a leggy seedling recoverable.

Harden off for a week and plant out only after the last frost. They are completely frost tender.

Pinching out, weekly, on cordons only#

Every leaf joint on a cordon produces a side shoot. Left alone each one becomes a full stem with its own leaves and flowers, and the plant puts its energy into growing rather than ripening.

So once a week, snap out each side shoot while it is small, a couple of centimetres at most. Fingers are better than secateurs, which spread disease between plants.

In late summer, pinch out the growing tip too, once the plant has as many trusses as it can realistically ripen. In an average season that is four or five trusses outdoors and six or seven under cover. After that the plant should be finishing what it has, not starting more.

Watering: consistency beats volume#

This is the section that prevents most tomato problems, because three separate complaints are the same underlying issue.

Split skins happen when the skin sets at one size and then a heavy watering swells the flesh faster than the skin can stretch. Blossom end rot, the dark sunken patch on the base of the fruit, is a calcium uptake failure caused by the water supply stopping and starting, not by a shortage of calcium in the soil. And flowers dropping without setting is often drought stress.

All three are fixed the same way: water little and often rather than drought followed by a flood.

Key points

• In hot weather a container tomato may need water twice a day. Check by pushing a finger into the compost rather than guessing.
• Water the compost, not the leaves. Wet foliage invites blight and mildew.
• Mulch containers and beds. It evens out the moisture more effectively than any watering routine.
• Bigger pot, better outcome. Thirty litres minimum, forty for a cordon.
• Adding calcium for blossom end rot almost never helps, because the calcium is usually already there.

Feeding, and when to start#

Not until the first fruit has set. Feeding a young plant pushes leaf growth at the expense of flowers, and a huge green tomato plant with three fruits on it is a well fed plant.

Once fruit has set, use a high potassium tomato feed weekly, or every second watering for containers. Potassium is what supports fruiting; nitrogen is what makes leaves.

Never feed a plant that is dry. Water first, feed second, or you risk scorching the roots.

Stop feeding a couple of weeks before you expect to finish picking. By then the plant is ripening rather than building.

Blight, and recognising it in time#

Blight is the thing that ends outdoor tomatoes in a wet summer, and it moves faster than people expect.

The signs: dark brown patches on leaves, often with a pale yellowish halo, brown streaks on the stems, and fruit turning brown and firm from the shoulders down. In warm humid weather a healthy plant can be finished inside a week.

There is no cure once it is established. What you can do:

Remove and bin

Not compost. Bag affected foliage and fruit and dispose of it. Spores overwinter on debris.

Grow under cover

A greenhouse or polytunnel keeps foliage dry and dramatically reduces blight risk. This is the single most effective measure.

Choose resistant varieties

Blight resistant varieties exist and are genuinely useful outdoors. Not immune, but they buy weeks.

Space and ventilate

Air movement dries foliage. Crowded plants blight first.

Water at the base

Wet leaves in the evening is exactly the condition blight wants.

Potato blight and tomato blight are the same organism, so do not grow the two next to each other if you can avoid it.

Ripening and the end of the season#

Tomatoes ripen on warmth rather than sunlight, so the plant does not need to be in full sun for fruit to colour up.

Late in the season, remove the lower leaves to improve air movement and let light onto the trusses, pinch out the top, and stop feeding.

When frost threatens, pick everything including green fruit. Green tomatoes ripen indoors in a paper bag, faster with a banana in it, or they make chutney. Fruit left outside once nights turn cold will not ripen and will rot.

What it costs#

A packet of seed

$3 to $6, and it contains far more than you need for several years.

Three young plants

$10 to $25 if you missed the sowing window, which is a perfectly reasonable way to start.

One 40 litre container

$25 to $70. The highest impact purchase for a container grower.

Canes or string support

$5 to $20 for cordons.

High potassium tomato feed

$8 to $18 a bottle, and one lasts a season for several plants.

Grow bags

$4 to $10 each, and honestly too shallow for a good cordon. Use them for bush varieties or double them up.

Where this needs adjusting#

In a short or cool season, grow under cover if you possibly can, choose early ripening varieties, and expect fewer trusses. Pinch the top out sooner.

In a hot climate, afternoon shade helps, flowers can drop above about 35C regardless of watering, and the watering demand roughly doubles.

Indoors on a windowsill, choose a dwarf bush variety, expect a modest crop, and hand pollinate by tapping the flower stems, since there is no wind or insect movement to do it.

Where the guidance here comes from#

The three-problems-one-cause framing for splitting, blossom end rot and flower drop is the most useful thing I know about tomatoes, and I learned it by treating them as three separate problems for two seasons. For variety choice, blight resistance and feeding the RHS advice on growing your own is the reference I check, and Garden Organic is good on blight management without spraying, which for a home grower is mostly about cover, spacing and variety.

The short version#

Check cordon or bush first. Sow six to eight weeks before your last frost, plant out after it. Pinch side shoots weekly on cordons only. Water little and often, at the base, in a pot of at least 30 litres. Feed high potassium once fruit sets, never before. Watch for blight in warm wet weather and bin it rather than composting it.

Related reading#

• How to start a vegetable garden: where tomatoes fit in a first year.
• Container gardening: pot volume, which decides most tomato outcomes.
• Vertical gardening: growing cordons on strings for far more fruit per square metre.
• Garden planner: sowing dates and why they are worth writing down.