Watering and Feeding Cherry Tomatoes Through the Season

Steady moisture matters more than quantity

Almost every cherry tomato problem that is not an insect comes back to swings in soil moisture. A plant that dries hard and then gets a soaking splits its ripening fruit within hours, because the skin on a small fruit has far less give than the skin on a large one. Your aim is a soil that never gets bone dry and never sits saturated, which is a duller target than watering deeply once a week but a much more useful one.

In open ground with a mulch, that usually means a thorough soak every four or five days in warm weather and nothing at all for a week after heavy rain. Check with a finger rather than a schedule: push it in two inches (five cm) at the edge of the leaf canopy. Damp means wait. Dry and crumbly means water, and water the soil, not the leaves.

1. Test at the canopy edge, not at the stem The soil by the stem stays damp long after the feeding roots at the canopy edge have dried. Test where the roots actually are.
2. Water in the early morning The plant takes it up before the heat, and the foliage dries within the hour. Evening watering leaves leaves damp overnight, which is how leaf spot spreads.
3. Mulch two inches deep Straw, grass clippings or plastic across the root zone halves the evaporation and takes most of the swing out of the soil. This is the single most effective anti-splitting measure in open ground.
4. After a downpour, stop Do not water for several days after heavy rain, even if the surface looks dry. Adding water to already wet soil is what splits fruit.

Containers dry out and starve faster

A cherry tomato in a 14 inch (35 cm) pot in midsummer can drink two gallons (eight liters) a day. Water until it runs freely from the drainage holes, and empty any saucer afterwards, because a pot standing in water suffocates its roots within a day or two. In a heatwave, do it morning and evening rather than doubling the morning dose.

All that water flushes nutrients straight out of the pot, so containers need feeding weekly from the moment the first fruit swells, not every two or three weeks as in open ground. If the compost has pulled away from the sides of the pot, push it back with your fingers first, otherwise everything you pour runs down the gap and out of the bottom.

Start feeding at first fruit set, then never stop

Hold off on fertilizer until the first fruit on the lowest truss is pea sized. Feeding a young cherry tomato is the classic mistake: it is vigorous enough already, and extra nitrogen at that stage gives you a magnificent plant that flowers late and drops what flowers it makes. Whatever compost you dug into the bed carries it comfortably to first fruit.

Once fruit is setting, though, a cherry tomato needs feeding for far longer than a slicing tomato does, because it is still filling trusses late in the season when a beefsteak has finished. Use a high-potassium tomato feed every ten to fourteen days in the ground and weekly in a pot, right through to your last picking. Plants that run out of food in late season give you thin-skinned fruit that splits at a touch.

1. First feed at pea-sized fruit Scatter a handful of balanced granular fertilizer in a ring at the canopy edge, eight inches (20 cm) clear of the stem, and scratch it into the surface.
2. Switch to high potassium once picking starts A tomato feed with roughly twice as much potassium as nitrogen keeps the fruit coming and stops the plant running to leaf.
3. Log the date every time Feeding from memory ends in either a starved plant or a nitrogen-drunk one. Write down each application and glance at the last date before you feed again.

Look at the plant before every feed. Tightly inward-curling tips with a very thick stem mean skip this one. Pale, thin, open growth with small flowers means feed a little sooner than planned.

Read the plant instead of counting weeks

A cherry tomato tells you what it needs in the shape of its growing tip and the behavior of its trusses. The tip curling hard inwards with dark, brittle-looking leaf and a stem thicker than your thumb is too much nitrogen. A tip held open and pale, with a stem narrowing towards the top, is a plant running out. Both are easy to see from a few feet away once you know what to look at.

The trusses are the second gauge. A cherry truss should be a bare stalk that ends in flowers. When a truss starts producing small leaves along its length, or ends in a leafy shoot instead of a flower, the plant has more nitrogen than it can use and the flowers on that truss will set poorly.

Why cherry tomatoes split, and what actually stops it

Splitting is the defining cherry tomato problem. The fruit is small, the skin is thin, and a fruit at full color has almost no capacity to stretch. When the roots suddenly take up more water than the skin can accommodate, it splits, usually in fine rings around the shoulders or in a single line from the stem. It happens overnight and almost always after rain or a heavy watering on dry soil.

Three things reduce it dramatically and nothing else makes much difference. Mulch, so the soil moisture never swings hard. A rain cover over the row while fruit is coloring, even a simple sheet of clear plastic across the tops of the stakes. And picking every two or three days so that no fruit sits at full color waiting for the next downpour.

1. Pick ahead of forecast rain Anything showing full color, and anything past the halfway point, should come off before a downpour. Half-colored cherry fruit finishes indoors in two days.
2. Never let the soil go bone dry It is the dry-then-wet cycle that splits fruit, not the wet part on its own. Consistent moisture is the whole trick.
3. Roof the row, leave the sides open Clear plastic over a rail on top of the stakes keeps rain off the root zone. Leave both sides open so air still moves and the plant does not cook.

Blossom end rot on a cherry tomato

A sunken black patch on the base of the fruit is blossom end rot. It is a water problem, not a disease, and it is much less common on cherry types than on large-fruited ones because a small fruit is easier for the plant to supply with calcium. When it does show up on cherry tomatoes, it is nearly always a container that dried out hard, or a plant that has been fed heavily with nitrogen.

Pick off any affected fruit, because it will not recover and the plant will keep spending on it. Then fix the watering rather than reaching for a calcium spray. If it appears on one or two fruit on the first truss and nowhere else, ignore it entirely; that is a plant settling in, and it corrects itself.

1. Remove marked fruit at once It will not size up and it rots on the plant, which draws in fruit flies and mold.
2. Even out the moisture, then wait a truss Mulch, water consistently, and check the truss above. If that one is clean, the problem is solved.
3. Miss the next nitrogen feed Excess nitrogen blocks calcium uptake. If the growing tip is curling inwards, skip a feed and the next truss usually comes through clean.