Coastal hedging: the salt and wind tolerant plants that survive down south

Quick answer: On an exposed southern coast, put Ozothamnus leptophyllus (tauhinu) and Ficinia nodosa on the front line where the spray lands, Muehlenbeckia complexa or Veronica (Hebe) 'Wiri Mist' behind that if you want something clipped, and Olearia dartonii or Kunzea ericoides for height and shelter. Leave taupata and karo to the northern coasts. Both are frost tender.

There's a moment on a coastal property where you walk past the end of a shelter row and the wind stops. Same paddock, same afternoon. On one side the grass is flat and you're leaning into it, and four steps the other side you can hear a bee working the flowers.

Then there's the other version. Every plant on the seaward side brown to halfway up, the ones tucked behind them green as anything. Same order, same day in the ground. Something on that site sorted them out, and down here the cold usually gets the blame for it.

What actually kills plants on an exposed coastal site?

Salt drying them out, mostly. Wind finishing the job.

Salt arrives as spray and mist, lands on the foliage and then pulls moisture back out of the leaf tissue. The leaf burns from the edge inwards, windward face first, and it happens whether or not there's water in the ground. You can have a soaking wet soil profile and a plant dying of thirst above it.

Wind does its own version without any salt involved. It strips moisture off new growth faster than young roots can put it back, and it abrades the leaf surface until the plant stops trying to grow on that side altogether. That's why an exposed hedge goes lopsided long before it goes brown.

Cold is the thing everyone names first and it's rarely the deciding factor on a coast. Invercargill, Bluff and the Catlins are milder than their reputation. The Otago Peninsula the same. What sorts plants on those sites is salt and constant wind, plus a growing season that's shorter at both ends than a northern coast.

Why doesn't the usual coastal plant list work down here?

Because most of it was written for a warm coast.

Search "salt tolerant plants NZ" and you'll get taupata and karo near the top of nearly every list. Both deserve to be there. Neither is the right call for a southern site.

Coprosma repens, taupata, has excellent salt tolerance and grows fast on a beachfront. Its natural range runs from North Cape down to about Greymouth, and it's frost tender, particularly while young. Pittosporum crassifolium, karo, sits in the same camp. Its original distribution was roughly the top half of the North Island, Te Paki south to about White Cliffs and East Cape, and while it takes moderate frost once established it's frost sensitive getting there.

We don't grow either. Not on principle, and not because they're bad plants. They're the answer to a question about Mount Maunganui, and you're asking one about Riverton.

Which plants take the salt best?

Two, if you want a front line that holds while everything behind it establishes.

Ozothamnus leptophyllus (tauhinu) is the one I'd reach for first. It grows naturally in coastal shrubland right through to subalpine country, and the tough little grey-green foliage handles both salt spray and wind. It wants high light and free-draining ground, so banks, sand and lean stony soil suit it better than a heavy wet flat.

Ficinia nodosa (knobby club rush) is the low one. It grows in sand dunes, sandy beaches and salt marshes around the country and it's rated hardy to frost, drought, wind and salt drift, which is an unusual four to get in a plant that costs what a sedge costs. The roots bind loose sand, so on a dune face or a sandy bank it holds the ground while the shrubs get away. It'll also sit in a wet spot without sulking, which most of the front-line plants won't.

What can I clip into a hedge on the coast?

Two again, at different heights.

Muehlenbeckia complexa (pohuehue) takes wind, salt spray and dry ground once it's established, and of the Muehlenbeckias it's the best one for trimming. It's vigorous, so it responds to clipping rather than sulking about it, and you can shear it into a proper formal face. The trade-off is that same vigour. Give it a job and a boundary, or it'll go and find its own.

Veronica (Hebe) 'Wiri Mist' is the low formal option, a hebe by any other name. It tolerates coastal conditions, light frost and dry spells once away, sits at about a metre by a metre left alone, and is usually kept between 50 and 75cm as a hedge with a light trim after flowering. Formal spacing is around 40cm, or 80cm if you want it informal. The honest limit sits in that phrase "light frost". On a coastal site that's fine. Take it inland to a hard-frost pocket and I'd want a season or two of evidence before promising anything.

What if I want height and shelter, not a hedge?

Olearia dartonii (twiggy tree daisy) is a fast, grey-leaved shrub that gets to roughly 3m by 2m, carries fragrant white flowers in spring, and is a coastal plant by origin that also handles cold and high-country exposure. It gets used as a shelter pioneer for exactly that reason. For a hedge or shelter line, space it 1 to 1.2m apart.

Kunzea ericoides (kanuka) is the taller option, out to around 8m by 4m, and it'll take trimming. It handles dry and poor soils, wind and salt air, with moderate frost tolerance once established. On a big exposed site the kanuka line is what lets the rest of the planting grow, because everything behind it sits in the lee.

What about Griselinia, then?

It works on the coast. Wet ground is what kills it.

Griselinia littoralis is a coastal species, wind and salt tolerant, so on exposure alone it belongs on this list. Its weakness is underfoot. It hates sitting in wet ground, and phytophthora root rot in heavy soil is what usually kills a Griselinia hedge, not the sea air. A free-draining coastal bank is close to ide

al for it. A flat paddock corner that holds water all winter is where you'll lose it, salt or no salt.

Same goes for any exposed site. Look down before you look out to sea.

Should the shelter be solid or let the wind through?

Let it through. A solid wall makes the problem worse.

Shelter design guidance is consistent on this. A semi-permeable barrier of roughly 40 to 60% porosity acts as a filter and gives the widest area of protection behind it. Wind hitting something solid gets forced up and over, then drops back down on the far side as turbulence, and that turbulence does more damage than the straight wind it replaced. Anyone who has watched a plant thrash itself to bits three metres behind a close-boarded fence has seen it happen.

The other number to hold on to is height. A windbreak slows the wind meaningfully for roughly ten times its own height downwind. So a 3m Olearia line covers about 30m of ground behind it, a 6m kanuka line about 60m. That's how you set the gap between shelter rows on a big property instead of guessing.

Does the advice change on other coasts?

The same species travel fine up the east coast. What changes is how hard you have to work to get them established.

North Otago and South Canterbury, so the Oamaru and Timaru coast, run drier and warmer in summer than the Southland coast. Salt is still salt, but establishment failures there come down to water more often than exposure, so a watering plan for the first two summers matters as much as the species list.

Inland from any of those coasts, the Canterbury nor'wester is its own event. It arrives warm and takes moisture off new growth at a rate young roots can't match. Shelter porosity matters more there than any frost rating on a label.

Shipping north is the natural place to make the hardened-stock argument. Stock grown outdoors in cold, wet, windy Southland conditions has already met worse weather than most sites up the line will serve it. Being straight about it, in Tauranga or Whangarei that hardening counts for less, because nothing up there is really testing it.

Common questions

How close to the sea is too close?

There isn't a line on a map. Salt carries a long way inland in a good blow, but the plants that cop it worst are the ones in the first row with nothing in front of them and nothing overhead. If a site takes visible spray, plan on the front row being sacrificial for the first few years while it builds up a crust of growth that shields the rest.

Can I just put up windcloth instead?

Use both. Windcloth or a temporary shelter fence through the first two or three years gives young plants a chance to get their roots down, and it comes out once the planting can hold its own. Check the porosity rating on the cloth rather than buying the tightest weave, for the same reason a solid fence causes turbulence.

Do I need to water coastal plantings? The wind makes everything feel damp.

Yes. Salt and wind both pull water out of the leaves, so the plant loses moisture faster than an inland one even in a wet season. Water through the first two summers on any exposed site.

Will salt build up in the soil and poison it?

On most coastal sites the rain washes it through, and the damage sits on the foliage rather than in the root zone. Truly saline ground, like a low flat that takes tidal or storm water, is a different situation and calls for salt-marsh plants rather than hedging. Ficinia nodosa is the one on this list that already grows in that ground.

What grade should I be ordering for an exposed site?

A bigger grade carries more reserve into a rough first summer, which counts for a lot when the wind is taking moisture off it daily. Smaller grades still establish well, cost less across a long boundary, and take the wind better because there's less top on them.

Get the front row right and everything behind it becomes easy. Get it wrong and you'll be replanting the same six metres every second winter.

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