Stress & salt · The wiki · Learning hub

How is it communicating to you?

That’s the question Steve wants you asking of your crop. The plant is the scorecard, and it tells you when it’s struggling. Say this year’s three degrees hotter. As Steve tells it, the plant says, “Oh, Steve, I’m struggling with this.” Hear that, and you can work with it.

Stress is anything that pushes a plant off its plan: heat, a cold snap or a frost, a dry spell, waterlogging, wind, salt, a pest, even a big hit of fertiliser. Every crop meets some of it every season. What counts is when it comes, how ready the crop is, and whether you’re reading what it tells you.

“How is it communicating to you? That’s the question you want to ask, and when you find that out, then everything you do is according to the plan.”

— Steve, on reading the plant

Survival mode

A plant under stress looks after itself first. It shuts the pores in its leaves to hold on to its water, and that shuts out the carbon dioxide it makes its sugars from, so the engine slows right down. In real heat it can burn sugar faster than it makes it. It stops growing, and it drops the flowers and young fruit it can’t carry. Push it far enough and it finishes early.

The underside of a leaf, magnified: a jigsaw of pale green skin cells, and in the middle a pore, open between two plump, bean-shaped cells. — A plant under stress looks after itself first. It shuts the pores in its leaves to hold on to its water, and that shuts out the carbon dioxide it makes its sugars from, so the engine slows right down. An illustration, simplified.

The same pore, closed: its two cells slack and lying close together, the gap shut to a line. — A plant under stress looks after itself first. It shuts the pores in its leaves to hold on to its water, and that shuts out the carbon dioxide it makes its sugars from, so the engine slows right down. An illustration, simplified.

Steve reads every sap report for stress, and survival mode is one of the things his bean report digs into.

When it hits matters

The same hot week doesn’t cost the same all season. In the middle of leaf growth, a crop slows down, then picks up again when the weather turns. At flowering, a dropped flower doesn’t come back: in beans, it’s a pod lost. Through cell division, the cells that aren’t made can’t be filled later, however good the rest of the season is. And near the end, it can bring the finish forward before the crop has filled.

A bush bean plant at picking time, eight long green pods hanging among its leaves. — Leaf grows back after a hot week. A flower dropped at flowering doesn’t. An illustration, not measured results.

The same bean plant with five pods; three stalks hang bare where pods would have been, each with a dashed outline of the pod it lost. — Leaf grows back after a hot week. A flower dropped at flowering doesn’t. An illustration, not measured results.

That’s why Steve’s programs are built around the stages. Know when your crop’s critical stages fall, and you know which forecasts to worry about.

Salt and chloride

When Steve writes up a sap report, stress gets a look of its own, and salt and chloride with it.

A little chloride is a nutrient: the plant uses it in its engine, and to open and close its pores. A lot of it, with sodium, is a stress two ways. Salty water around the root is harder to draw up, so the plant goes thirsty in wet ground. And what it does draw up builds up in the leaves, until their tips and edges burn, the older leaves first.

A young bean plant in dark, wet soil with a faint white crust on top, cut away to show its roots. — Salt is a stress two ways: salty water is harder to draw up, and what the plant does draw up builds up in its leaves until they burn. An illustration, simplified.

Salt is a stress two ways: salty water is harder to draw up, and what the plant does draw up builds up in its leaves until they burn. An illustration, simplified.

Salt comes in the water, from a bore or a river running low, from a rising water table, and in what goes on. Some fertilisers carry a lot of salt, and potassium often goes on as potassium chloride. Crops differ a lot: avocados, beans and strawberries are among the most sensitive to salt, and barley and cotton among the most tolerant. So the wrong fertiliser at the wrong time can hurt your plants.

In potatoes, Steve sees it at planting. The chloride and nitrate in a big load of fertiliser under the seed tell the plant to grow leaf, right when it should be setting tubers.

Have the crop ready

You can’t stop a heatwave. What you can do is go into it with a crop that’s ready.

The foundation in. Cell walls built with calcium, boron and silicon stand up better to heat and wind, and hold their water better.
Potassium, once it’s earned. Potassium works the pores and moves the plant’s water. Steve’s rule still stands: the foundation first, then potassium.
The engine running. A crop whose leaves are working well has sugar to spend when it’s under pressure. The Photosynthetic efficiency page has more.
No soft growth going into the heat. Lush, sappy growth full of unfinished nitrogen is the first to wilt and burn, and the first the pests find.
The water steady. Big swings are a stress in themselves, and through sizing they can split the fruit.

A firm, upright young bean plant, an even healthy green, with a few small white flowers. — You can’t stop a heatwave, but you can go into it with a crop that’s ready: the foundation in, potassium once it’s earned, and no soft growth. Lush, sappy growth full of unfinished nitrogen is the first to wilt and burn, and the first the pests find. An illustration, simplified.

You can’t stop a heatwave, but you can go into it with a crop that’s ready: the foundation in, potassium once it’s earned, and no soft growth. Lush, sappy growth full of unfinished nitrogen is the first to wilt and burn, and the first the pests find. An illustration, simplified.

After it’s been hit

Walk it first, and ask what it’s telling you. Where is it worst: the sandy rise, the low spot, the end rows? Is it in the old leaves or the new? Then test the sap and put it beside the last test, so you’re reading the trend, not one bad day. Find out why before you add more: a mineral that shows short after a stress may be there, just not moving, and the roots need a chance to come back. A foliar can get a mineral into the leaf while the roots are struggling.

Where it fits in a program

Know when each of your crop’s stages falls, and watch the forecast ahead of every one. A hot week costs something different at each.
Put a sap test before the stage where stress usually hits in your district, and one after, so you can see what it did.
Hold the nitrogen going into a hot spell.
Test your water for salt. A bore can change fast in a dry year.
Watch the chloride in what goes on, most of all at planting.
Tick the week’s weather on your Crop Walk, so it sits beside what you saw.
Bring the hard ones to the live Q&A.

Stress and salt