Tomatoes and capsicums

Start with the box

Steve starts every crop with one question: tell me what your market wants. For fresh tomatoes and capsicums, it’s the box: fruit of the right size, evenly coloured, firm, clean of marks, and able to hold up on the way to the shelf. A fruit with a rotten end, a split or a blotchy colour is one you grew, picked and paid to cart, then threw out. Processing tomatoes are judged on other things: the sugar and the colour in them.

So the yield that counts is what packs out: Steve’s recoveries. And most of what’s lost from the box is decided weeks before it’s picked.

A shallow tray of ripe tomatoes, all the same size and the same even, glossy red. — The box is what the buyer pays for: fruit of the right size, evenly coloured, firm and clean, that holds up on the way to the shelf. A fruit with a rotten end, a split or a blotchy colour was grown, picked and paid to cart, then thrown out. An illustration, simplified.

Three ripe tomatoes: one with a dark, sunken patch at its blossom end, one split round its stalk and down its side, and one ripened blotchy, with yellow and green patches. — The box is what the buyer pays for: fruit of the right size, evenly coloured, firm and clean, that holds up on the way to the shelf. A fruit with a rotten end, a split or a blotchy colour was grown, picked and paid to cart, then thrown out. An illustration, simplified.

A plant that flowers as it fruits

A trellised tomato keeps growing all season. Every few leaves it puts out a truss of flowers, and it keeps going: while the bottom trusses fill and colour, the ones above are still flowering and setting. Capsicums and eggplants do the same, with a flower or two at each fork. So every stage of the crop is happening somewhere on the plant at once, and the plant is always sharing its sugar between new leaves and fruit.

Walk up one plant and you can read the whole season in it. At the bottom, a truss colouring. Above it, fruit filling, and above that, fruitlets still making their cells. At the top, the newest truss is in flower, under the growing tip. Each truss passes through every stage in its turn, and the leaves between them feed them all.

A tall tomato plant on a single stem: at the top, the growing tip and a truss of yellow flowers; below it, a truss of small green fruitlets, then a truss of full-size green fruit, and at the bottom a truss turning red. — A tomato flowers at the top while it fills and colours fruit below, so every stage of the crop is on the plant at once, all fed by the same leaves. An illustration, simplified.

That makes it a balance, like cotton. Push it with nitrogen and water and it grows leaf and drops flowers. Load it with fruit too early and it stalls, and the trusses above set poorly. The crop you want keeps growing steadily, and keeps setting as it goes.

Flowers set or drop

A tomato flower pollinates itself, but its pollen has to be shaken loose: by the wind outdoors, by a bee, or by a vibrating wand under cover. And the pollen is fragile in heat. On days over about 32°C, or nights that stay above about 20°C, much of it dies, and flowers drop without setting. Capsicums drop their flowers in heat too. A run of hot weather at flowering shows up weeks later as a gap in the trusses.

A tomato truss on its stem, carrying five small round green fruit. — A tomato’s pollen is fragile in heat. On days over about 32°C, or nights that stay above about 20°C, much of it dies, and the flowers drop without setting. A run of hot weather at flowering shows up weeks later as a gap in the truss. An illustration, simplified.

The same truss with only two fruit, and three short, dry stubs where the other flowers dropped. — A tomato’s pollen is fragile in heat. On days over about 32°C, or nights that stay above about 20°C, much of it dies, and the flowers drop without setting. A run of hot weather at flowering shows up weeks later as a gap in the truss. An illustration, simplified.

That’s one of the crop’s critical stages. It’s where the foundation (calcium, boron and silicon) has to be on time: boron for the pollen and the set, and calcium for the cells to come.

A short burst of cells

Once a tomato sets, it makes its cells fast, but only for about a week or two. Then it stops dividing, and grows for another month or so by filling the cells it has, before it colours. So the number of cells a tomato will have is mostly settled in its first week or two, and with it much of how big it can grow.

It’s Steve’s cell division window, truss by truss. Each truss opens its own, so the foundation has to be there all through the weeks the crop is setting, not just at the first flowers.

Blossom-end rot: calcium in the wrong place

The best-known fault in tomatoes and capsicums starts as a small, water-soaked spot at the blossom end, the end away from the stalk, where the flower was. It spreads into a dark, sunken, leathery patch. In a capsicum it’s often a pale, papery patch on the side, near the end. It’s a shortage of calcium, but it’s rarely a soil short of calcium. It’s calcium in the wrong place.

Calcium travels in the water, and the water goes where it evaporates: mostly to the leaves. A fruit gives off little water, so it gets little calcium, and inside the fruit, the calcium comes in at the stalk end and thins out towards the blossom end. From about one to three weeks after flowering, a young fruit swells fastest, faster than its calcium can follow it in. Then a hot, dry day or a gap in the watering sends the water to the leaves instead, and the cells at the blossom end collapse. Salt at the roots makes it worse, because the roots take up less calcium to start with.

A young tomato plant: a fine-haired green stem with jagged leaves, and a truss holding two small green fruit and two flowers. — Calcium goes where the water goes, mostly to the leaves, even when the soil has plenty. A fruit gets little, and its blossom end is last in line: that’s where blossom-end rot starts. An illustration, simplified.

A young green tomato cut in half from its stalk to its tip, its seeds in two chambers of jelly. At the blossom end, at the bottom, is a dark, sunken, leathery patch: blossom-end rot. — Calcium goes where the water goes, mostly to the leaves, even when the soil has plenty. A fruit gets little, and its blossom end is last in line: that’s where blossom-end rot starts. An illustration, simplified.

So the answer is mostly water: steady, never swinging from wet to dry, and above all as the fruit sets. Then keep the competition down. Too much potassium, magnesium or ammonium at the roots crowds the calcium out, and fast, soft growth pulls what there is into the leaves. Calcium sprayed on young fruit helps the fruit it lands on, a little. By the time you see the rot, that fruit was lost weeks ago, so look after the trusses still setting.

Fill and colour

Once a fruit has made its cells, it fills them with water and sugar, and colours. This is where potassium has earned its place. It drives the sugar into the fruit and builds its flavour. A fruit short of it ripens blotchy, with patches that stay green or yellow, and walls that stay hard and grey. Give potassium before the foundation is in, though, and it crowds out the calcium the young fruit need. It’s the same order Steve teaches for every crop.

A ripe tomato on its truss, round and glossy, an even deep red all over. — Once a tomato has made its cells, it fills them with water and sugar, and colours. Potassium drives the sugar into the fruit. Short of it, the fruit ripens blotchy, with patches that stay green or yellow. Give it once the foundation is in, though: before that, it crowds out the calcium the young fruit need. An illustration, simplified.

The same tomato ripened blotchy, with patches of green and yellow-orange left on its shoulders and side. — Once a tomato has made its cells, it fills them with water and sugar, and colours. Potassium drives the sugar into the fruit. Short of it, the fruit ripens blotchy, with patches that stay green or yellow. Give it once the foundation is in, though: before that, it crowds out the calcium the young fruit need. An illustration, simplified.

Heat matters here too. The red in a tomato doesn’t form well above about 30°C, so fruit ripening in a heatwave colours orange or yellow, and fruit out in full sun can scald. A good canopy over the trusses is shade as well as an engine.

Cracking

A near-ripe fruit that gets a sudden drink, after a dry spell or a storm, swells faster than its skin can stretch, and splits: in rings around the stalk, or in lines down from it. Steady water is the answer again, and a skin built with calcium may stretch further.

A near-ripe tomato on its truss, round, smooth and glossy, its skin whole. — A near-ripe fruit that gets a sudden drink, after a dry spell or a storm, swells faster than its skin can stretch, and splits. Steady water keeps it whole, and a skin built with calcium may stretch further. An illustration, simplified.

The same tomato split: cracks in rings around the stalk, and cracks running down its side. — A near-ripe fruit that gets a sudden drink, after a dry spell or a storm, swells faster than its skin can stretch, and splits. Steady water keeps it whole, and a skin built with calcium may stretch further. An illustration, simplified.

Reading the leaves

Where the yellow shows on a tomato says where to look. Yellow between the veins of the older, lower leaves is often magnesium, and tomatoes show it easily: the heavy potassium they’re fed for fruit fill crowds magnesium out at the root. Yellow on the newest leaves at the top points to a mineral that barely moves once it’s in: iron, manganese, zinc or sulfur. The Mobile and immobile minerals page explains why. Confirm it with a sap test before you spray.

A young tomato plant, its soil cut away to show its roots: its lowest leaves yellow between green veins, the leaves above green, and a truss of small green fruit. — Where the yellow shows says where to look. Between the veins of the older leaves, it’s often magnesium: the heavy potassium a tomato is fed for fruit fill crowds it out at the root. On the newest leaves, it points to a mineral that barely moves once it’s in: iron, manganese, zinc or sulfur. Confirm it with a sap test before you spray. An illustration, simplified.

Where the yellow shows says where to look. Between the veins of the older leaves, it’s often magnesium: the heavy potassium a tomato is fed for fruit fill crowds it out at the root. On the newest leaves, it points to a mineral that barely moves once it’s in: iron, manganese, zinc or sulfur. Confirm it with a sap test before you spray. An illustration, simplified.

Cucumbers, zucchini and melons

Cucumbers, zucchini and melons are a different family from tomatoes. They work differently. Most carry separate male and female flowers on the same plant, and bees have to carry the pollen from one to the other. A female flower that gets too little makes a fruit that’s crooked or pinched at the end, or drops it. So the bees count: keep them in mind when you spray. And a melon makes most of its sugar in its last couple of weeks before picking, from the leaves it still has, so keep them working to the end, with potassium and magnesium.

Part of a zucchini plant: a big lobed leaf, a male flower on a long thin stalk, and a female flower on the tip of a small young zucchini. — Cucumbers, zucchini and melons mostly carry separate male and female flowers, and bees carry the pollen from one to the other, so keep the bees in mind when you spray. A female flower that gets too little makes a fruit that’s crooked or pinched at the end. And a melon makes most of its sugar in its last couple of weeks, from the leaves it still has. An illustration, simplified.

Two young cucumbers side by side: one straight and even, the other curved and pinched at its blossom end. — Cucumbers, zucchini and melons mostly carry separate male and female flowers, and bees carry the pollen from one to the other, so keep the bees in mind when you spray. A female flower that gets too little makes a fruit that’s crooked or pinched at the end. And a melon makes most of its sugar in its last couple of weeks, from the leaves it still has. An illustration, simplified.

The season at a glance

About 120 days from planting. The days are a guide: the crop’s stage is the clock. Build yours in the program builder.

1 · Transplant to establishment days 0–14

Roots into the soil before the tops take off.

How you know it’s here The young plants hold up through the afternoon, and new leaves start at the top.

What matters most: Phosphorus Calcium Zinc
2 · Vegetative growth days 14–35

Build the canopy: the engine for all the fruit to come.

How you know it’s here Growing fast, with new leaves and shoots every few days, and the first flower buds still closed.

What matters most: Manganese Magnesium Nitrogen
3 · First flowers and fruit set days 35–55Sap test

Flowers set or drop in these weeks. Boron and calcium have to be there on time.

How you know it’s here The first flowers open, and the first small fruit hold as the petals fall.

What matters most: Boron Calcium Silicon
4 · Early fruit growth days 55–75Sap testCell division

Cells divide in the young fruit, and calcium gets in fastest now, so keep it coming.

How you know it’s here Young fruit growing on the first trusses or nodes, while more flowers open above.

What matters most: Calcium Boron Silicon
5 · Fruit fill and picking days 75–120

Fill and colour the fruit while new flowers keep setting. Potassium has earned its place now.

How you know it’s here The first fruit colour up or reach picking size, while the plant keeps flowering and setting.

What matters most: Potassium Magnesium Sulfur

Where it fits in a program

Know your box: size, colour, firmness and shelf life, and what’s cost you packouts before.
Get the roots away at transplanting, with phosphorus close by.
Have boron and calcium on before the first flowers, and keep the foundation coming through every truss that sets.
Water evenly, every day, through fruit set. Most blossom-end rot and cracking is water.
Save potassium for fruit fill. By then the crop has earned it.
Sap test as the first flowers open, and through the setting weeks, while there’s still time to act.

“Earn the right to use potassium. Don’t put it out there previously.”

— Steve, on potassium

Toma­toes and capsi­cums