Cotton

Start with the bale

Steve starts every crop with what the market wants. In cotton, it’s the lint, classed bale by bale. The class looks at how long the fibre is and how strong, its micronaire, a reading of how fine and how mature it is, its colour, and how much leaf and trash is through it. A bale that’s short, weak, too coarse or not mature enough, or stained by rain on the open bolls, is discounted.

So the profit isn’t only the bales to the hectare. It’s the bales that make their class: Steve’s recoveries, in fibre.

A sample of white cotton lint, with a tuft of long, fine fibres drawn out of it and laid straight. — Cotton is sold as lint, classed bale by bale: how long the fibre is and how strong, its micronaire, a reading of how fine and how mature it is, its colour, and how much leaf and trash is through it. So the profit isn’t only the bales to the hectare: it’s the bales that make their class. An illustration, simplified.

Another sample, dull and stained yellow-brown in patches, flecked with bits of dry leaf, its drawn-out fibres short. — Cotton is sold as lint, classed bale by bale: how long the fibre is and how strong, its micronaire, a reading of how fine and how mature it is, its colour, and how much leaf and trash is through it. So the profit isn’t only the bales to the hectare: it’s the bales that make their class. An illustration, simplified.

A plant that fruits as it grows

Cotton is a shrub grown as a crop, and it doesn’t stop growing to fruit. It keeps adding nodes up its main stem. A node is where a leaf joins the stem. From about the fifth or sixth node up, each node puts out a fruiting branch. Each fruiting branch carries its fruit one position after another, and the first position, closest to the main stem, makes the biggest and surest boll. So the plant is building its frame and setting its crop at the same time.

That makes cotton a balance. Too much nitrogen and water, and it grows rank: tall, leafy and shedding its fruit. Too little, and it loads up early and stops growing before the crop is big enough. The crop you want grows steadily, and holds its fruit as it goes.

A tall cotton plant with long gaps between its nodes and big, dark, lush leaves, its fruiting branches mostly bare. — Cotton fruits as it grows, so it’s a balance. Too much nitrogen and water, and it grows rank: tall, leafy and shedding its fruit. Too little, and it loads up early and stops growing before the crop is big enough. The crop you want grows steadily, and holds its fruit as it goes. An illustration, simplified.

Cotton fruits as it grows, so it’s a balance. Too much nitrogen and water, and it grows rank: tall, leafy and shedding its fruit. Too little, and it loads up early and stops growing before the crop is big enough. The crop you want grows steadily, and holds its fruit as it goes. An illustration, simplified.

Squares: hold the fruit

The first fruit is a square: a flower bud wrapped in three frilly bracts. It takes about three weeks to flower. Every square held is a boll to be, but a cotton plant always sheds some, and under stress it sheds far more: a dry spell, a run of hot or cloudy days, rank growth, or insects. Nearly everything it sheds is a square, or a boll in its first two weeks. An older boll, it almost always keeps.

A cotton fruiting branch with three broad, lobed leaves, a green boll in frilly bracts, a young boll with a dry pink flower on its tip, and a square: a pyramid-shaped green bud in three frilly bracts. — Cotton’s first fruit is a square: a flower bud wrapped in three bracts. Every square held is a boll to be. Under stress, a cotton plant sheds far more of them, and nearly everything it sheds is a square or a young boll. An older boll, it almost always keeps. An illustration, simplified.

The same branch with only the older boll left on it; the square and the young boll lie fallen below it, their bracts flared and yellowing. — Cotton’s first fruit is a square: a flower bud wrapped in three bracts. Every square held is a boll to be. Under stress, a cotton plant sheds far more of them, and nearly everything it sheds is a square or a young boll. An older boll, it almost always keeps. An illustration, simplified.

Insects are one of those stresses. Mirids and caterpillars take squares and young bolls, and sap-suckers like aphids and whitefly crowd onto soft, lush growth. Steve’s question comes first: why is that pest there? A crop pushed rank with nitrogen is the one they find. The Pests and plant health page has more.

Squaring is where cotton starts to set its crop, and the foundation goes in for it: boron and calcium to help hold the squares, and silicon for tougher tissue. On each walk, count the first positions that still carry their fruit. That’s the crop’s retention, and it tells you early how the season is going.

Each fibre is a single cell

A cotton flower opens creamy white in the morning and is pollinated that day. By the next day it’s turned pink, and a few days later it drops, leaving a small green boll. Flowering starts at the bottom of the plant and climbs it, a node every few days.

Inside the boll, every fibre is one single cell, growing out of the seed’s coat. It starts on the day the flower opens. For about three weeks it grows long, and that sets the fibre’s length: a dry spell then means short fibre. Then it stops lengthening, and fills its wall with cellulose, layer on layer, until the boll opens. That sets its strength and its maturity. A boll opens about seven or eight weeks after its flower.

It’s Steve’s cell division idea, flower by flower. Each young boll makes its cells in its first weeks, and its fibres start the day it flowers. A crop flowers for five or six weeks, so the foundation has to be there the whole way through, not just at first flower.

A cotton branch with a broad lobed leaf, and at its end a creamy white flower cupped in three frilly green bracts. — One fruiting position, followed over time. Each fibre is a single cell: it grows long first, then thick. An illustration, simplified.

The same branch with a young green boll cut in half: seeds wrapped in short, wet, white fibres. — One fruiting position, followed over time. Each fibre is a single cell: it grows long first, then thick. An illustration, simplified.

Cut-out, and filling the bolls

As the bolls load up, flowering climbs closer to the top of the plant. When there are only four or five nodes left above the highest white flower in a first position, the plant has cut out: it stops adding fruit, and puts what it makes into the bolls it has. Count the nodes above the top white flower on each walk, and you’ll see cut-out coming.

A young cotton plant: an upright stem with broad lobed leaves, and short fruiting branches carrying green squares, each a flower bud in three frilly bracts; two places near the stem are empty. — A cotton plant fruits as it grows. Two counts on each walk tell you how the season’s going: the first positions still holding fruit, and the nodes left above the top white flower. An illustration, simplified.

The same cotton plant weeks later, taller: green bolls low down, a creamy white flower and a pink one higher up, and a few nodes of young leaves above them. — A cotton plant fruits as it grows. Two counts on each walk tell you how the season’s going: the first positions still holding fruit, and the nodes left above the top white flower. An illustration, simplified.

Now the plant has earned its potassium. It needs plenty, and the bolls are a big draw on it. Short of it, the leaves mottle yellow, then bronze and drop before the bolls are full. The bolls stay light, and the fibre can come out shorter and weaker. Magnesium and sulfur keep the leaves working to the end.

Opening, and a clean finish

The bolls open from the bottom of the plant up. What you want now is a crop that finishes: the top bolls filled and open, and the leaves ready to come off cleanly when it’s defoliated for picking. Late nitrogen works against all of it. It feeds new leafy growth, holds the top bolls back, and makes the leaves harder to get off. So hold the nitrogen at the finish, and get it picked before rain stains the lint.

The same cotton plant at the finish: open bolls of fluffy white lint from the bottom of the plant to the top, its leaves turned yellow, red and bronze. — The bolls open from the bottom of the plant up. What you want now is a crop that finishes: the top bolls filled and open, and the leaves ready to come off cleanly when it’s defoliated for picking. Late nitrogen works against all of it, so hold the nitrogen at the finish. An illustration, simplified.

The same cotton plant given late nitrogen: open bolls low down, but a dark green, leafy top with small green bolls still shut. — The bolls open from the bottom of the plant up. What you want now is a crop that finishes: the top bolls filled and open, and the leaves ready to come off cleanly when it’s defoliated for picking. Late nitrogen works against all of it, so hold the nitrogen at the finish. An illustration, simplified.

The season at a glance

About 180 days from planting. The days are a guide: the crop’s stage is the clock. Build yours in the program builder.

1 · Planting to establishment days 0–20

An even stand in cool spring soil: roots down before the tops take off.

How you know it’s here The seedlings are up, with two round seed leaves, then the first true leaf.

What matters most: Phosphorus Zinc Calcium
2 · Early growth to first square days 20–45

Build the frame: the nodes and fruiting branches that will carry the crop.

How you know it’s here True leaves come one node at a time up the main stem, with no squares yet.

What matters most: Manganese Magnesium Nitrogen
3 · Squaring days 45–65Sap test

Every square held is a boll to be. Boron and calcium on time help hold them.

How you know it’s here The first squares show: tiny flower buds, each wrapped in three frilly bracts.

What matters most: Boron Calcium Silicon
4 · Flowering and boll set days 65–100Sap testCell division

Cells divide in each young boll in its first weeks, flower by flower. Keep the foundation there right through, and have the nitrogen on by peak flowering.

How you know it’s here The first flowers open creamy white, low on the plant. They turn pink the next day, and drop to leave a small boll.

What matters most: Calcium Boron Silicon
5 · Boll fill days 100–145

Fill the bolls. The plant has earned its potassium now, and it needs plenty of it.

How you know it’s here The flowering has climbed to the top of the plant and slowed: that’s cut-out. The bolls are filling.

What matters most: Potassium Magnesium Sulfur
6 · Boll opening to picking days 145–180

Let the top bolls finish and open. Hold the nitrogen: this late, it only feeds regrowth.

How you know it’s here The first bolls crack open, from the bottom of the plant up, showing white lint.

What matters most: Potassium Calcium

Where it fits in a program

Know what your bales are classed on, and what cost you last season: length, strength, micronaire or colour.
Build the frame early: an even stand, and a plant growing steadily into its fruiting branches.
Have boron, calcium and silicon in by first square, and keep the foundation coming right through flowering.
Feed the growth the fruit can carry, and no more: rank growth sheds fruit.
Save potassium for when the bolls fill. By then the crop has earned it, and it needs plenty.
On each walk, count the first positions holding fruit, and the nodes above the top white flower. Sap test from first square and through flowering, while there’s still time to act.

“Build the foundations, build the house, fill it with potassium. Now you’ve got yield and quality.”

— Steve, on the order of a program

Cot­ton