Control weeds and predators

Woman holding up weeds after maintenance day

Control weeds

To ensure the success of your restoration project, focus time and effort on weeds. Weeds can smother native plantings unless they are actively controlled. Learn about different weed types and methods to tackle them.

Why is it important?

Weeds or pest plants threaten the indigenous biodiversity of Aotearoa New Zealand. Without intervention, pest plant species have the potential to re-shape our natural landscape and completely eradicate some of our taonga native species.

Weeds compete with native plants for resources and space. Before planting natives, prepare the area by removing weeds. Control weeds for the first 3-5 years to ensure your seedlings survive. The time you spend will decrease once the native plants grow in.

Where to start

DairyNZ has identified seven simple steps to keep your waterways weed-free! They are: Identify the weed, start small, work in stages, plant up, take care, removal and weed disposal.

Head to page 7 of DairyNZ's Waterway Technote on Pest Plants to learn more about these steps.

Types of weeds

1. Trees & shrubs (woody plants)

They often replace native plants, change the composition of plant communities and can prevent native plant regeneration.

Tree examples: willows, wattles, privet and wilding pines
Shrub examples: gorse, heather, broom and barberry
2. Herbs (non-woody plants)

They can overtop small plants, crowd out native plants and prevent native seedling regeneration.

Terrestrial examples: Tradescantia, pampas, wild ginger
Aquatic example: oxygen weed
3. Vines

They smother native trees and forest canopies.

Examples: ivy, japanese honeysuckle, mothplant, banana passionfruit and blue morning glory

Learn how to identify weeds

The following resources provide databases with photos and descriptions of common weeds from across Aotearoa New Zealand.

Two woman pulling out wild ginger weeds from planting site

Weed Control Techniques

Your approach will depend on the types of weeds you are targeting, the tools available, and your preferred approach. Read on for information on organic and chemical approaches.

Pictured: Wild Ginger

Spray-free methods

We recommend spray-free methodologies or using minimal spray to control the worst weeds. There are many ways to prevent weed growth and remove weeds without the use of chemicals.

Weed Mats

Putting weed mats around plants stops weeds from germinating and helps retain water
Use biodegradable products (e.g. woollen carpet offcuts, cardboard, newspaper) rather than plastic weed mat/polythene
Secure them with pegs to prevent them from moving or damaging your plants

Mulch

Spreading organic material around the base of your native plants will prevent weed growth and stop the soil from drying out. Ideal materials include untreated sawdust, bark or wood chips
A minimum depth of 10cm is required to stop weed growth. Check on your mulch - animals, wind and flooding can move it around and it breaks down overtime

Plant guards

Plant guards protect seedlings from weeds, strong weather conditions and animal pests. Check out FutureEcology for a biodegradable option
Install when seedlings are planted. Remove once the plant grows above the height of the guard

Hand-releasing

Hand-releasing means releasing the native from weeds growing around its base
For small sites, or if you have a large team, manual weed control can be perfectly effective
Wear gloves, pull back the weeds and flatten them down around the base of the plant (this can act as a mulch)
Regular re-visits will be necessary as some weeds will re-sprout.

Tips from our partners

Using tools like a flax cutter/”shark” can help to quickly clear weeds around your seedlings. Matuku Link's restoration team swears by them!
Ring-barking can effectively kill some species without chemical application. Waiheke Resources Trust has found that ring-barking tree privet is an effective way to kill them naturally. As the privet dies it provides shelter for new native plants.

Chemical Methods

There are a lot of groups and farmers choosing spray-free methods. However, spray-free methodologies can be time consuming and labour intensive, so aren’t always possible.

Herbicide Best Practice

Read the label and follow all precautions
Understand H&S requirements (Personal Protective Equipment is essential)
Less is better
Only spray on dry, wind-free days
Choose the right herbicide. Make sure it is effective on the species you are targeting
Gels are more effective on woody species than aerial sprays
Consider spot spraying twice before planting rather than broadcast spraying the entire area.
You may need to follow up every few months. Successful eradication can take years!
Use marker dye in your spray so that you (& others) can see where you’ve sprayed
Avoid spraying near waterways. Herbicides can be extremely toxic to aquatic flora and fauna

Further guidance on weed control methods

Your Weed Control Guide by Forest & Bird provides guidance on control methods for specific weeds
Weedbusters also has detailed information on control methods for different weeds
This practical video by DairyNZ demonstrates some common plant-releasing techniques
If you are interested in undertaking foliar weed control on a large-scale, learn about how agrichemicals work and the risks involved through a Growsafe course

Weed Disposal

Some weeds are safe to leave onsite as mulch (e.g. grass cuttings). Others must be removed to stop further spread (e.g. Tradescantia, moth plant, blackberry).

There are lots of options when it comes to green waste disposal. Check out your local refuse station to see if they accept green waste, or organise a weed collection service.