Now Is the Time to Eradicate Willows and Restore NZ Natives

Marlborough, NZ - [December 2025] — Invasive willows continue to wreak havoc across New Zealand's waterways, but the summer months present the perfect window for action, according to local restoration expert Terence Stewart, the Founder and Owner of Native Restorations.

"People don't realise how incredibly aggressive willows are," says Terence. "They're adaptive, fast-growing, and thrive near water, which is why they're choking out our native plants and completely altering streamside ecosystems. We need to get rid of them now, before they take over."

Native Restorations, which operates throughout Marlborough, Kaikōura and Nelson, is calling on landowners to take advantage of the summer season to drill and fill invasive willow trees, a proven method that kills the tree without the need for immediate removal.

Why Summer Is the Best Time to Kill Willows

According to Stewart, willows are most vulnerable when they're actively growing and absorbing water. This makes summer the perfect time for treatment.

"Between December and April, the trees are pulling up water and nutrients fast. If you drill the base of the tree and fill the holes with herbicide now, the chemical will be taken through the plant's system far more effectively," he explains.

The "drill and fill" method involves drilling holes at the base and along exposed roots, spaced evenly, and immediately filling them with a 50/50 solution of water and glyphosate (like Roundup). Within one to two weeks, the tree will show signs of decline, and within a few months, it can be safely dropped and removed.

"Let the tree die standing. That's the trick. If you cut it first, it becomes chemically resistant. You need the leaves and canopy to help draw the herbicide through the system," says Stewart.

He also advises not to mulch the tree immediately after dropping or poisoning.

"It's not uncommon to hear of projects where a poisoned tree has not been left long enough and used for mulch, this can seriously damage or kill your new native plantings as the tree will still contain chemicals."

Plant Natives First, Kill Later

Rather than clearing and replanting all at once, Stewart recommends a strategic approach: plant your natives first, then kill the willow.

"It sounds backwards, but using the willow's canopy can actually protect young native plants from harsh sun and wind. Just don't plant directly under big limbs that could fall. Once your natives are established, you can poison and drop the willow and let the native species take over."

Climbers Like Old Man's Beard Also a Major Threat

Willows aren't the only invaders causing damage. Vines such as Old Man's Beard and banana passionfruit are equally destructive, especially in native bush. These climbers smother canopies, wrap around trunks, and often kill the very trees they latch onto. Many will argue that banana passionfruit are pretty and tasty, but this little climbing sucker blankets canopies and kills native bushlands.

"Climbers are sneaky. One central root, but they spread fast and wrap tightly. You can't just rip them out as you'll damage the tree they're clinging to. You need to kill the root and let them die naturally over time," Stewart explains.

Call in the Experts or Do It Right

While property owners can take action themselves, Stewart stresses the importance of following correct techniques and chemical handling, or calling in professionals if unsure.

"A lot of people want to do the right thing, which is great. But if you don't do it properly, willows and vines will bounce back stronger. They're survivors. A single willow branch left in a creek can regrow into a whole new tree."

A Better Future Starts With Better Planting

Native Restorations works with landowners, community groups, and councils to remove pest plants and reintroduce native species across the top of the South Island.

"When we remove willows and replant with natives like harakeke, carex, kōwhai, or mānuka, we're not just restoring the look of the land, we're rebuilding ecosystems," Stewart says. "It's about giving nature a fighting chance."

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