Weathering the wind

GLYN CHURCH
Last updated 07:50 30/11/2012

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Last week we were up at Dawson Falls, looking at the shrubs on the National Park boundary. That got me thinking about how wind- hardy our native plants are. Most of us never think about it, and those who do, like landscapers, tend to take it for granted.

If a landscaper needs plants for a windy section they automatically start with native shrubs. For home gardeners with a new section or an exposed site, then native shrubs are going to be your standby for two reasons - the obvious wind tolerance and also the speed of their growth. They give you a visual screen and shelter in just a short time.

There's a reason our natives are so resilient. We're surrounded by ocean, far more than you might imagine. It's only when you see a map of the world with New Zealand centre stage it sinks home. We're cast adrift with no protection. Those Roaring Forties winds attack our tiny nation on a daily basis, but there's the added problem of salt-laden winds which are much more damaging to softer plants.

New Zealand is generally recognised as the windiest country in the world, not that there's a league table or anything. Some quibble and say the Falklands, but that's just part of Argentina (whoops) like the Chathams are part of New Zealand. So naturally as the windiest place we have the most resilient native plants to cope with those conditions.

Years ago I worked with Jane Hunter of Hunters Wines (name dropper) when she first came to New Zealand from Australia, to teach viticulture. Jane couldn't fathom why there was so much emphasis on shelter belts and hedges in the student assignments. "In Australia, all we have are fences" was her justification. It didn't take long, living in windy Wellington, for her to realise why anyone needs shelter from the storms.

For softer plants like grapes, wind is a three-fold problem. We are aware of how severe winds can topple trees and shrubs, but the wind also tears at soft leaves, crushing them until they are useless.

But there's another factor. Plants draw water up from the ground to boost the internal cells, but also to cool the plant. It acts like a ventilation system, because fresh water cools the plant as it travels up to the leaves and evaporates through the leaf pores.

Strong winds take this moisture away much more quickly and so the plant becomes dehydrated and dies. The soil, too, loses moisture, thus increasing the suffering felt by the plants. The easy way for gardeners to overcome this problem is to apply a thick layer of mulch, say woodchip or bark. This keeps the soil moist and cool and reduces the dehydration.

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So in a sense there are two kinds of hardiness for plants. One is the leaves and the other the stems or trunks.

Lots of our native shrubs have tough glossy leaves that resist moisture loss or any superficial damage from breaking and tearing. But often these plants topple at ground level during a gale. Pittosporums and akeakes or dodonaea would be typical of this, and if you get to them in time and restake them they eventually develop enough strength to cope. Others like the Griselinia littoralis are super stable and hardly ever blow over, and have super waxy leaves.

Those waxy leaves shared by the shiny taupata, or Coprosma repens, are the best for resisting salt winds as any salt deposits are washed off in the next downpour. Even the huge leaf puka Meryta sinclairii can shed salt and even more remarkably can cope with storms. To look at it you would think the first breeze would tear those huge paddle leaves off the tree. Another surprising coast hardy tree is the fine leaf kowhai.

Most gardeners don't have enough room for trees, but if you want a wind hardy tree then natives should be your first port of call. Pohutukawa, puriri, pigeonwood, karaka, kohekohe, ngaio - they're all amazingly tough. Even totara are resilient and breeze through cyclones. New Zealand natives adorn the streets of San Francisco, where the people have realised just how wind- tolerant our native trees are.

If you fancy going exotic then look for plants from other windy places such as South Africa with leucadendrons and proteas, or the Mediterranean with lavenders, brooms and rock roses.

After Wellington, New Plymouth is said to be the next windiest city, and the whole coastline is constantly being lashed by storms, so we need to look for these wind-hardy plants.

Of course we can alleviate the effects of wind by planting shelter hedges. You might imagine that solid walls and fences would do a better job, but it's not true as this just causes more turbulence. A hedge allows air to pass through and will filter the wind and reduce its strength. Even grass benefits from shelter and if farmers were to plant a series of hedges across the prevailing wind, their grass growth would be significantly improved.

When you see lush grass waving in the wind, every blade is losing water at too fast a rate, and both the ground and the plant are losing valuable moisture. In our desperate race to grow more grass we replace hedges with fences, but the reality is the increased wind strength is counterproductive.

Much as we might hate the wind at times, it does have its benefits. The ocean currents create the winds, bringing us plentiful rain to grow grass for our income. Perish the thought, but should the currents ever change, and the winds cease to blow, we might have regular droughts like the east coast. Tourists and sunbathers might like it, but it wouldn't be good for our economy.

- Taranaki Daily News

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