Salt and wind exposure

What you are looking at

Damage with a direction to it. The leaves along one side of a shrub are brown and dry around the margins, the buds on that side have failed to open, and the other side of the same plant is untouched. Draw a line through the garden and everything to windward of it is scorched while everything in the lee of the wall or the hedge is clean.

On the coast this follows a gale, usually within a week, and it happens in summer as readily as in winter. Inland beside a treated road it appears in spring, along the boundary, in a strip a few metres deep.

Evergreens show a slower version through late winter. Needles brown from the tip back and leaves go dull and leathery over several weeks, with no single cold night to point at.

Two different injuries with the same shape

Wind on its own dries a plant out. A leaf sits inside a thin layer of humid air that it has created by evaporating into it, and that layer slows further loss. Moving air strips it away and the leaf loses water at several times the rate. Where the roots can keep up, nothing happens. Where they cannot, the margins die, and the margins go first because they are furthest from the veins.

That is why an evergreen browns in February. The leaves are still losing water to every dry wind that passes, the soil is cold or frozen, and the roots cannot draw enough to replace it. The plant dies of drought with wet ground around it.

Salt makes the same injury worse and adds one of its own. Airborne droplets land on the leaf, the water evaporates, and the salt is left behind. Sodium and chloride cross the cuticle, travel in the water stream, and concentrate at the leaf margin where the water evaporates and the salt cannot. Chloride reaches levels the tissue cannot tolerate and the margin dies, which produces a browning that is sharper and further in from the edge than wind alone gives.

Salt in the ground is the third case and it works from below. Road salt washed off a pavement raises the concentration in the soil so that roots cannot take up water at all, and the plant shows drought symptoms in wet ground. Sodium also strips calcium off the clay particles and collapses the soil structure, so the ground sets hard and drains badly, which finishes off whatever the salt started.

Why the fence made it worse

Anyone who has put up a close-boarded fence to shelter an exposed garden has probably noticed that the plants immediately behind it did not improve.

Wind meeting a solid barrier goes over the top, and it comes back down behind it in a rolling eddy that can be more violent than the airflow it replaced. The sheltered zone behind it is short, and beyond that the plants get turbulence from above rather than a steady wind from the side.

A permeable barrier does something different. Letting roughly half the wind through slows it without deflecting it upwards, so the air behind stays smooth and the sheltered zone runs to around ten times the height of the barrier. A 2 m hedge therefore does useful work 20 m into the garden, which no wall of the same height comes close to.

That is the argument for hedges, shelter belts and windbreak mesh over fencing on any exposed site, and it holds whether the wind is carrying salt or not.

Reading the ground before you plant

The plants that grow untended on an exposed coast have small leaves, or thick waxy ones, or a coat of fine hairs. Each of those reduces how much spray sticks and how fast water goes, and none of them is an accident.

Walk the ground within a few hundred metres of where you are planting and note what is thriving without help. That local list beats any general one, because it has already been tested against the exact combination of exposure, salt, soil and winter you are dealing with.

Where the site is inland and the salt comes off a road, the exposure question disappears and the soil question takes over. There the useful trait is tolerance of sodium in the root zone, and the practical answer is usually to keep the salt out with a barrier rather than to find a plant that will put up with it.

What to do about it

Plant a permeable windbreak rather than building a solid fence, and expect shelter for about ten times its height.

Build the shelter in layers, with a sacrificial outer row.

Choose species that already thrive untended nearby, and read the leaves for small, waxy or hairy.

Screen new planting with mesh or hessian for its first two or three winters.

Plant in spring on a cold exposed site so the roots are working before winter.

Use grit rather than salt on paths you control, and screen the boundary beside a salted road.

Hose the foliage down with fresh water after a salt-laden gale that no rain follows.

Soak salted ground repeatedly in spring to wash the salt below the roots, and work organic matter in to hold the structure together.

Wait for growth to start before cutting out what looks dead.

What it gets mistaken for

Sun scorch takes the leaves the light falls on, so it picks out the top and the sunny side rather than the windward side.

Frost blackens soft growth all over the plant on a single morning, and the damage matches a date rather than a direction.

Wind rock is the same wind working underground, loosening the plant at the base and opening a water-filled socket around the stem.

Fertiliser scorch burns the lowest leaves all round the plant and leaves a crust on the soil.

Drought scorches evenly in dry ground, which is what separates it from an evergreen browning over wet winter soil.

Honey fungus and root disease kill a plant from one side too, and the tell is underground rather than overhead, so lift a little soil at the base and look at the bark before settling on the wind.