Foliar or soil · The wiki · Learning hub

Four ways in

The program builder asks it of every pass: how does it go on? At planting, onto the soil, through the water, or onto the leaf. Each way in has its job, and a good program uses each one for what it does best.

A young bean plant, cut away below the ground, with its taproot and fine roots spreading through red soil. — The four ways a pass goes on, on one plant. An illustration, not to scale.

The four ways a pass goes on, on one plant. An illustration, not to scale.

At planting: there from the start

What goes in with the seed is there before the crop needs it. Steve’s poppy plan starts here: a planting blend with root fungi, to get the tiny seed through its slow first three weeks. The Poppies page has the plan.

But don’t load it up. In potatoes, Steve’s view is that a big load of fertiliser under the seed sets up a fight at the root. Potassium out-competes everything else, and the chloride and nitrate in the same load tell the plant to grow leaf when it should be setting tubers. The Potatoes page has more.

A young potato plant, its hill cut away: the old seed piece, fine roots, and stolon tips hooked over and swelling into small, round young tubers. — Keep what goes under the seed modest. A big load of fertiliser there sets up a fight at the root: potassium out-competes everything else, and the chloride and nitrate in the same load tell the plant to grow leaf when it should be setting tubers. An illustration, simplified.

The same potato plant, its leaves lusher and darker, its stolons running on, long and thin, with no young tubers swelling. — Keep what goes under the seed modest. A big load of fertiliser there sets up a fight at the root: potassium out-competes everything else, and the chloride and nitrate in the same load tell the plant to grow leaf when it should be setting tubers. An illustration, simplified.

Onto the soil: slow, and it builds

The big amounts go on the soil: lime and gypsum, and much of the nitrogen, phosphorus and potassium. The roots, and the life around them, take them up as the crop grows, and some of what’s left, like the phosphorus and lime, builds up over the seasons. It’s the slow way, and the soil has a say in how much of it the plant gets.

That’s Steve’s point about the root zone. It’s not what’s in the soil that counts, it’s what happens around the root. Put nitrate in, the pH around the root goes up, and the trace minerals you put on aren’t released. The Soil health page has more.

Through the water: little and often

Fertigation feeds through the irrigation, straight to the root zone, a little at a time, all season. It suits what the crop needs steadily while it grows and fills, like potassium through sizing, once the crop has earned it. Whatever’s in the water comes too, so check it for salt.

A young tomato plant with green fruit, cut away below the ground: a black drip line on the soil beside its stem, an emitter by the stem, and fine roots spreading through red-brown soil beneath it. — Fertigation feeds through the irrigation, straight to the root zone, a little at a time, all season. It suits what the crop needs steadily while it grows and fills. Whatever’s in the water comes too, so check it for salt. An illustration, simplified.

Onto the leaf: on time

A foliar goes on at the stage that needs it. Here’s a bean crop’s sap report, as Steve tells it. Through cell division, calcium dropped hard, so next season a calcium foliar goes in at that stage. The Cell division windows page has it.

“We have to get that calcium up into there. So next time you grow your beans, you know what we’re going to do? When we get to there, we’re going to get calcium foliar spray.”

— Steve, on a bean crop’s report

A foliar spray puts a mineral into the plant at the stage it matters, even when the soil’s holding it back or the roots are struggling. Foliars suit the minerals the plant can’t move around itself, like calcium and boron (in most crops), which have to land on the new growth they’re for. The Mobile and immobile minerals page explains why. They suit the trace minerals a crop needs only a little of, like manganese and zinc. But a leaf takes in only so much at a time. A foliar tops a crop up at the right moment. It doesn’t feed the whole crop.

Why the foliars follow the stages

Each stage is short, and some minerals have to be in the new tissue right then. The soil can’t be counted on to deliver them on the day: a cold snap, a dry spell or the wrong pH, and the roots can’t get them.

Steve’s poppy plan has a first foliar spray to overcome the lag of those slow first weeks. The Poppies page has it.

Getting a foliar to work

In the cool of the day. Early morning or evening, when it’s cool and the spray dries slowly. Not in the heat: then the spray dries too fast and can burn, and the plant has shut the pores it breathes through. The Stress and salt page has more.
Not just before rain. Give it time to soak in.
On the growth it’s for. Calcium and boron (in most crops) barely move once they’re in, so time them to the new growth.
Weak and often, not strong and once. Too strong a mix scorches the leaf.
Small and dissolved. A leaf takes a spray in through tiny pores in its waxy skin. What’s dissolved and small gets through most easily: the smaller, the faster. And it goes in best while the spray’s still wet on the leaf. That’s why a small chelate, like a small chelated calcium, gets in better than a big one.

A magnified cross-section of a leaf: a waxy skin over rows of green cells, with one clear drop of spray sitting on top. — A leaf takes a spray in through tiny pores in its waxy skin: what’s small and dissolved goes in while the spray is still wet. Spray in the cool of the day, so it stays wet long enough. An illustration, simplified.

The same leaf section: the drop has dried to a pale crust, and the green cells under it have browned and collapsed. — A leaf takes a spray in through tiny pores in its waxy skin: what’s small and dissolved goes in while the spray is still wet. Spray in the cool of the day, so it stays wet long enough. An illustration, simplified.

In the tank

Some products don’t mix. Calcium with a sulphate can drop out of the tank as a solid, and silicates, the silicon products, don’t sit well with most things. Calcium and phosphorus lock up together unless the tank is kept acid. Phosphoric acid keeps it acid, so calcium acetate or calcium nitrate can go in with it and are much less likely to drop out. A chelator, like fulvic acid or amino acids, can keep calcium and a sulphate apart, but not calcium and a phosphate: the phosphate pulls too hard. The Jar tests page has why.

A litre jar with a lid, its mix gone clear on top, pale flakes drifting in it and a white layer on the bottom. — Calcium and a phosphate lock up together and drop out of the tank, unless the tank is kept acid, as phosphoric acid keeps it. A chelator, like fulvic acid or amino acids, isn’t enough on its own: the phosphate pulls harder than it holds. Jar test every new mix. An illustration, simplified.

The same jar, full of an evenly, faintly cloudy pale liquid. — Calcium and a phosphate lock up together and drop out of the tank, unless the tank is kept acid, as phosphoric acid keeps it. A chelator, like fulvic acid or amino acids, isn’t enough on its own: the phosphate pulls harder than it holds. Jar test every new mix. An illustration, simplified.

The program builder flags a pass that mixes what won’t sit together, and notes one kept acid. When it pencils passes in for you, silicon gets a tank of its own, a few days ahead of the rest. Sulphates go on a few days after the calcium. So do phosphates, unless phosphoric acid keeps the tank acid.

Before a new mix goes in the tank, check its pH and jar test it: a litre of the water you’ll spray with, and each product at the tank’s strength, added in the tank’s order. Let it stand half an hour. If it settles out, clots or gels in the jar, it will in the tank. A clear jar is a good sign, not a promise. A bucket test does the same at the farm’s scale, and shows more: whether the mix clumps or settles as it stands, and whether it all runs through a fine filter, as it has to through the sprayer’s. Once your sprayer’s in, the program builder works out the jar’s amounts for each foliar pass. And the label is the law.

Where it fits in a program

The base goes in at planting and onto the soil. Keep what goes under the seed modest.
Time the foliars to the stages, for the minerals that have to be in the new growth then.
Fertigate little and often through sizing, if you have the system.
Jar test a new mix, and spray in the cool of the day.
In the program builder, each pass says how it goes on. Its checks flag a mix to jar test, and passes that could share a trip.