Watering and Feeding Medium Tomatoes for Even, Full-Sized Fruit

Why steadiness matters more at this fruit size

A medium tomato sits on the plant for roughly two months between open flower and full color, growing the whole time. Calcium, the mineral that keeps the blossom end sound, moves only in flowing water and only into tissue that is actively expanding. That means the plant needs an uninterrupted supply for weeks, not a good soak now and then. A cherry fruit finishes fast enough to shrug off a dry week. A medium fruit records it, as a black patch or a ring of splits.

Aim for soil that is never bone dry and never saturated. In open ground under 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 two inches (five cm) into the soil at the edge of the leaf canopy, where the feeding roots actually are, not next to the stem where it always feels damp.

1. Test at the canopy edge The soil beside the stem holds moisture long after the working roots at the canopy edge have dried out. Test where the roots are, not where the plant is.
2. Soak deeply, not often Half a gallon (two liters) or more poured slowly at the base beats a daily sprinkle. Shallow watering keeps roots near the surface where they cook in high summer.
3. Water in the early morning The plant takes it up before the day's heat and the foliage dries within the hour. Evening watering leaves leaves wet overnight, which is how leaf spot spreads.
4. Mulch two inches deep and keep it topped up Straw, clippings or plastic over the root zone halves evaporation and takes most of the swing out of soil moisture. It is the cheapest insurance against both blossom end rot and splitting.

Blossom end rot: the medium tomato's characteristic failure

A sunken, leathery black patch on the base of the fruit is blossom end rot. It is a calcium delivery failure, not a disease, and it is markedly more common on medium and large fruit than on cherries because a bigger fruit needs more calcium delivered over a longer period into tissue that is expanding faster. Almost all of your soil already has enough calcium in it. What has failed is the water carrying it.

The usual causes are a container that dried out hard, a heavy nitrogen feed that pushed leaf growth ahead of root supply, or root damage from hoeing too close to the stem. Pick off affected fruit immediately, because it will not recover and the plant keeps spending on it. Then fix the watering rather than buying a calcium spray, which barely penetrates the fruit skin and does not address the cause. Watch the next truss up: if that one comes through clean, you have solved it.

Splitting: rings on the shoulders and radial cracks

Medium tomatoes split in two distinct ways and the pattern tells you which mistake you made. Fine concentric rings around the shoulders come from slow, repeated moisture change over days, and they are ugly but shallow. A single deep crack running from the calyx down the side comes from a sudden surge, almost always rain or a heavy watering onto soil that had gone dry, and that one opens the fruit to rot within a day.

This size of fruit splits more readily than a beefsteak because the skin is under more tension relative to its thickness, and less readily than a cherry only because it has more mass to absorb the surge. The fix is the same in either case and it is not a product: keep the mulch on, water before the soil goes hard rather than after, roof the row with clear plastic while fruit is coloring, and pick anything at full color ahead of forecast rain.

1. Pick colored fruit ahead of a storm Anything past the halfway point in color should come off before heavy rain. It finishes indoors in two or three days with no real loss of flavor.
2. Never let the soil go hard between waterings It is the dry-then-wet cycle that splits fruit, not the wet part alone. A soil that stays evenly damp almost never splits fruit.
3. Roof the row, leave the sides open A sheet of clear plastic over a rail on top of the stakes keeps rain off the root zone. Open sides keep air moving so the canopy does not turn into a glasshouse.

Feeding: start late, then keep going

Do not feed until the fruit on the lowest truss is the size of a marble. Whatever compost you dug into the bed carries the plant comfortably to that point, and nitrogen applied earlier gives you a magnificent leafy plant that flowers late, sets badly and produces black-based fruit. This is the single most common self-inflicted problem on medium tomatoes.

Once fruit is sizing, feed every ten to fourteen days in the ground and weekly in a container, using a tomato feed with roughly twice as much potassium as nitrogen. Because each fruit takes two months to finish, a plant that runs out of food in late summer hands you pale, hard-shouldered tomatoes that never color properly. Keep feeding right through to your last picking.

Reading the plant instead of counting weeks

The growing tip and the shape of the trusses tell you what the plant needs from several feet away. A tip curled tightly inwards, very dark, on a stem thicker than your thumb is a plant with more nitrogen than it can use. An open, pale tip on a stem narrowing towards the top is a plant running out of food. Both are easy to see once you know to look, and both are more informative than any fixed feeding schedule.

Trusses are the second gauge, and on medium tomatoes they are unusually honest. A healthy truss is a bare stalk ending in flowers. When small leaves start appearing along the truss, or it ends in a leafy shoot instead of a flower, the plant is nitrogen-drunk and those flowers will set poorly. Check the truss shape before every feed and skip a round when it looks leafy.

Green shoulders and hard cores

A medium tomato that colors to a good red but keeps a hard yellow-green ring around the stem has had too much direct sun on the fruit, too little potassium, or both. Temperatures above 86F (30C) on the fruit surface stop the red pigment forming while the rest of the fruit ripens normally, which is why over-enthusiastic leaf stripping causes it so reliably.

Leave the leaves above each sizing truss in place so the fruit ripens in dappled shade, keep the potassium going, and in a heatwave put shade netting over the row through the afternoon. Fruit already showing green shoulders will not fix itself on the plant, but it is perfectly good eating once you cut the core out, so pick it and move on.

1. Stop stripping leaves above the fruit Every leaf above a sizing truss is shading and feeding that fruit. Only remove leaves below the truss you are actively picking.
2. Shade the row above 86F (30C) Shade netting through the afternoon keeps fruit surface temperature below the point where the red pigment stops forming.
3. Record which trusses did it Note the truss number and the week it happened. Two seasons of that tells you whether your row needs shading every year or only in exceptional heat.