How to Tackle Stubborn Weeds: Convolvulus, Blackberry, Kikuyu, and Couch

Extracts from ‘Edible Backyard’ – Growing Food Gardeners NZ’ by Kath Irvine, a legendary Kiwi gardening teacher and author.

Gardening is a battle against nature’s most persistent invaders, and some weeds are determined to win, but that’s not going to happen under the Cut’n’Paste watch! So here we go with another fantastic post full of tips for you – whether you’re a weekend warrior or a more full-time guardian of our natives.

Among the most troublesome to deal with (and the ones we get many emails about) are convolvulus, blackberry, kikuyu, and couch grass. Each presents unique challenges, which are amplified further when considering the unique environmental setting wherever it’s growing – but with the right strategies, you can reclaim your garden or land.

The following passages are adapted and re-printed with thanks from ‘Edible Backyard ⋆ Growing Food Gardeners NZ’ by Kath Irvine, a legendary Kiwi gardening teacher and author. Learn more at ediblebackyard.co.nz.)

Convolvulus: The Twisting Nemesis

Convolvulus is a relentless climber that thrives in a variety of conditions. It doesn’t care whether it’s in rich compost or heavy clay—it will spread aggressively regardless.

How to Control Convolvulus

• Smother It: On bare ground, lay carpet in spring before new growth appears. Keep an eye out for any shoots peeking out over summer and cut them back.
• Dig It Out: In autumn, when the soil softens, roll up the carpet and remove the tangled roots. Burn them or seal them in a black plastic bag until they rot.
• Plant Competitively: Fill the space with fast-growing, competitive plants that will outcompete convolvulus over time.
• Persistent Removal: Any regrowth should be traced back to its source and removed.
• Livestock Assistance: Chickens followed by pigs can weaken convolvulus over time, but complete elimination is rare.

Dealing with Convolvulus in Existing Plantings

If convolvulus is winding through your established plants, organic control is difficult. A precise, targeted application of Cut’n’Paste [Bamboo Buster], glyphosate gel developed by New Zealand park ranger Andy Spence, can be effective. Dabbing new growth each December has significantly reduced convolvulus in orchards and native plantings without the risks of spray drift. Cut’n’Paste is also working on a glyphosate-free alternative, which will be a welcome addition to any organic gardener’s toolkit.

Blackberry: The Thorny Invader

Blackberry thrives in open ground and along edges where soil life is lacking. If left unchecked, it can take over large areas quickly.

How to Manage Blackberry

• Small Areas: Hand grub the blackberry and let goats graze on the new shoots to weaken regrowth. Alternatively, use Cut’n’Paste [Bamboo Buster] to target stubborn patches.
• Larger Infestations: Use a digger to clear dense patches, then follow up with Cut’n’Paste and grazing.
• Long-Term Control: Improve soil health and plant dense, competitive vegetation to reduce blackberry resurgence.
• Consider Keeping Some: If space allows, leave a small patch for its delicious berries!

Kikuyu and Couch Grass: The Relentless Spreaders

Kikuyu and couch grass spread rapidly, with kikuyu running both above and below ground and couch grass (also known as twitch) creeping through the topsoil.

Controlling These Stubborn Grasses

• Smother & Suppress: Mow the grass down and cover with plastic until it dies off. Then lay thick cardboard, mulch heavily, and plant strong, competitive species.
• Build Soil Health: In veggie gardens, frequent weeding, composting, and mulching will weaken their hold over time.
• Vigilance is Key: Regular maintenance, including mowing, grazing, and mulching, will keep kikuyu and couch from taking over.
• Use Cut’n’Paste for Tough Areas: Where kikuyu is aggressively invading existing plantings, targeted application of Cut’n’Paste [Bamboo Buster] can help suppress it until other plants establish.

Final Thoughts

Weeds are persistent, but with the right approach, they don’t have to take over your garden. Whether you prefer organic methods or targeted herbicide application like Cut’n’Paste, a combination of suppression, soil improvement, and consistent maintenance is the key to long-term success. Keep at it, and soon, your garden will be thriving weed-free!

(Content adapted from ‘Edible Backyard ⋆ Growing Food Gardeners NZ’ by Kath Irvine. For more expert gardening advice, visit ediblebackyard.co.nz.)