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War on weeds

Jack Hobbs reveals the dark side of plants escaping from gardens, and shows us why conservation of our native bush needs to start at home.


Banana passion fruit - a vine that can quickly spread New Zealand has around 2,400 native plant species. Compare that with more than 19,000 plants that have been introduced. And more than 2,000 of those have now escaped into the wild and are posing a real threat to our environment.

These garden escapees have become an epidemic in parts of the country. They are aggressive, reproduce prolifically, spread quickly out of control, and dominate our native plants.

Blue morning glory - a quick-climbing vineFor example, a pohutukawa has germinated on the trunk of this phoenix palm up here — and down here, well, another little baby. Neither of these pohutukawas could have germinated on the foreshore below because there is a thick carpet of kikuyu grass there. In a lot of places pohutukawa is not regenerating naturally because an introduced plant has taken over its habitat.

This is Cornwallis Beach, one of my absolute favourite regional parks. You can understand why people built their baches here. While the baches have long gone, the plants from their gardens remain. In fact, they're doing very well indeed.

Wild ginger - forms a dense thicket smothering other vegetationFrom here I can see ginger, I can see a loquat. Clambering up a tree, there's a banana passion fruit — in fact, there's just an awful lot of stuff.

I'm with Scott De Silva, senior park ranger with Auckland Regional Council, who says the news on the weed front is pretty bad, particularly in Auckland.

"Auckland now has become known as the second worst weed place in the world, behind Hawaii. I'd say that's probably because of the similar climates we both have — wet and warm.

Climbing asparagus"This area had a series of baches along here, and a lot of these are garden escapees. It was settled really early, and people obviously brought plants to which they were attached and have just let them go wild.

"The plants behind us, for example, these plants have just taken over and the natives are really struggling."

In this area the worst weeds are ginger, climbing asparagus and blue morning glory, which are all hard to control, says De Silva.

Blue morning glory "A lot of them are replacing areas where natives should be. Their ability to persist in some of these environments — they've just taken over.

"Certain ones, like ginger, can persist under a canopy, and don't require a lot of light. We'll probably end up with a canopy of mature trees and no regeneration underneath that. We'll end up with an area full of weeds and very very few natives."

Looking around, most of the plants are well-known garden subjects. Agapanthus has spread down the side of this road, and blue morning glory is creeping over the top of the trees. The red-berried plant, cotoneaster, is ready to spread itself everywhere too.

The range of weeds is enormous. There are ground covers, perennials, climbers, shrubs and trees. There are shade lovers and sun lovers.

So how do we control them?

  • Weed bin In the Waitakere Ranges the council has been providing weed bins. When you pull a weed out of your garden or out of the wild, you can bring it here, chuck it in the bin, and stop the spread.

  • Never compost them because they will bounce back. Don't dump them, either. You saw what happened in Auckland, the world's second weediest place.

  • Plectranthus When you've cleared an area, don't stop there. Once we had an area here that was covered in ginger. Now it is covered in plectranthus, which is just about as bad a weed.

  • Plant something once you've cleared an area of weeds, preferably a vigorous native. Then a bit of follow-up to keep the weeds at bay until your native plants have matured.

It's very important that people look after plants that might escape from their gardens, says De Silva.

Some of the weeds are beautiful plants, but the potential of them getting into a park like this is devastating. Be aware of the potential of these plants, and if they have the ability to become invasive, watch them like a hawk.

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH

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Last updated: March 1, 2021