Wool Mulch: The Complete Guide for New Zealand Gardens

If you've ever wondered whether sheep's wool can be used in the garden, the short answer is yes. Wool can be used as a natural mulch around vegetables, fruit, flowers, trees and other plants. It covers exposed soil much like more familiar mulches such as straw, bark or wood chips, while bringing some useful characteristics of its own.

Here in New Zealand, wool is also something we have plenty of.

At Sustaina Grow, we've spent years working with New Zealand strong wool and developing practical ways to use it in gardens. This guide brings together what we've learned about using wool as mulch, where it works well, where it doesn't, and how to get the best results from it.

What is wool mulch?

Wool mulch is sheep's wool used as a protective layer over the surface of garden soil. Sustaina Grow has needle punched the wool into a mat form that has no viable seed and the perfect mulch for your garden. 

This wool mulch matting  can help with:

- suppressing weeds
- retaining soil moisture
- protecting the soil surface
- moderating soil temperature
- keeping some fruit away from wet soil
- gradually adding organic material as the wool breaks down

Unlike synthetic weed matting, wool is a natural fibre and will eventually biodegrade.

Why use sheep's wool in the garden?

Wool has some interesting properties that make it particularly suited to gardening.

1. Wool can help suppress weeds

One of the simplest benefits of mulch is blocking light from reaching the soil.

Wool can create a dense physical barrier over the soil, making it harder for new weeds to establish.

It isn't magic.

Persistent weeds can still find gaps, and established weeds should ideally be removed before the wool goes down.

But reducing exposed soil can significantly reduce the amount of ongoing weeding required.

Our tip: Spend a little extra time weeding properly before installing wool mulch. Starting with relatively clean ground gives the mulch a much better chance of keeping it that way.

2. Wool can help retain moisture

Bare soil can lose a surprising amount of moisture through evaporation, particularly during warm, dry or windy weather.

Covering the soil helps reduce that exposure.

Wool is also naturally able to absorb and hold moisture.

For gardeners, that can mean soil stays moist for longer between watering compared with leaving the surface completely exposed.

This doesn't mean you can stop watering.

Think of wool mulch as helping you make better use of the water you're already putting on the garden.

We're currently documenting our own side-by-side trials looking at moisture levels under wool compared with uncovered soil, and we'll add those results here once the trial is complete.

3. Wool helps protect the soil

Mulch isn't only about weeds.

Heavy rain, strong sun and wind all act directly on exposed garden soil.

A layer of wool provides a physical cover over the surface.

This is particularly useful around vegetable plants where soil would otherwise remain bare for much of the growing season.

4. Wool can help moderate soil temperature

Mulch acts as insulation between the soil and the surrounding air.

That can help reduce some of the rapid temperature changes experienced by exposed soil.

Wool's insulating properties are well known outside gardening too,  they're one of the reasons wool has been used in clothing and insulation for generations.

In the garden, that insulating layer can help create a more buffered environment around plant roots.

5. Wool eventually breaks down

This is one of the biggest differences between wool and plastic weed mat.

Wool isn't intended to stay in your garden forever.

Over time, weather, soil organisms and natural decomposition gradually break the fibre down.

Rather than eventually having to pull deteriorating pieces of plastic out of your garden, the wool becomes part of the soil environment.

How quickly this happens depends heavily on the form of wool, thickness, moisture, soil contact and local conditions.

Sustaina Grow Wool lasts 18 months.  ( However, this can be longer or shorter depending on conditions) 

Does wool add nutrients to the soil?

Wool isn't just carbon-based plant material.

Wool fibre is predominantly made from a protein called keratin and contains nutrients including nitrogen and sulphur.

As wool slowly decomposes, nutrients contained within the fibre can gradually become available within the soil system.

The important word here is slowly.

We wouldn't recommend treating a wool mulch mat as an instant replacement for every fertiliser your plants need.

Its primary job is mulch.

Any nutrient contribution happens gradually as the wool breaks down.

Is wool mulch good for vegetable gardens?

Yes. Vegetable gardens are one of the places we find wool particularly useful.

It can be placed around established plants including:

- tomatoes
- courgettes
- pumpkins
- brassicas
- strawberries
- garlic
- herbs
- beans
- chillies
- eggplants

The main thing is to leave enough room immediately around plant stems and crowns.
Don't tightly pack wet mulch against stems.

Is wool mulch good for strawberries?

Strawberries are one of our favourite applications for wool.

There are several reasons.

Strawberry plants tend to grow for long periods in the same place, weeds compete around their shallow roots, and fruit can end up sitting directly against damp soil.

A wool layer around the plants can cover the exposed ground while leaving the strawberry crown free.

It can help reduce weeds and create a physical layer between developing fruit and the soil below.

We've worked extensively with wool around strawberries, which eventually led us to develop our Strawberry Grow Pack specifically for this job.

Can you use wool mulch around garlic?

Yes.

Garlic is another crop where keeping weeds under control can be particularly helpful.

Garlic spends months growing in the ground, and weed competition during that time can mean a lot of ongoing maintenance.

Wool can cover the soil around the plants while allowing the garlic shoots to grow through designated openings.

This was the thinking behind our Garlic Grow Mats.

Does wool mulch stop slugs and snails?

This needs a more careful answer.

You will often see claims online that sheep's wool deters slugs and snails because of the texture of the fibre.

We don't think it's responsible to tell gardeners that wool will guarantee slug-free plants.

There are many factors involved, including moisture, how the wool is installed, the type of wool, slug pressure and the surrounding garden.

We're running our own practical trials to better understand how effective wool is as part of slug and snail management.

Until we have good evidence from those trials, we'd describe any deterrent effect as a potential additional benefit rather than a guaranteed method of slug control.

If slugs are a major problem in your garden, use wool alongside good garden hygiene and other appropriate control methods rather than relying on it alone.

How long does wool mulch last?

There isn't one exact answer.

Wool's breakdown rate depends on:

- thickness
- how densely the wool has been formed
- rainfall and irrigation
- temperature
- contact with soil
- microbial activity
- the particular wool product

A dense wool mulch mat can remain useful considerably longer than a thin scattering of loose wool.

As a general guide, some of our wool garden products can remain in place for around 18 months to two years, although individual conditions vary.

That's a feature rather than a flaw.

We want the wool to last long enough to do its job. and then naturally break down. Standard Sustaina Grow mulch wool is 600GSM.  However, we do change thickness for different products. 

How do you use wool mulch?

The exact method depends on whether you're using loose wool or a manufactured wool mat, but the principles are simple.

Step 1: Weed first

Remove existing weeds, particularly established perennial weeds.

Step 2: Water if necessary

If the ground is very dry, water the soil before covering it.

Step 3: Lay the wool

Cover the exposed soil evenly.

Avoid leaving large gaps where weeds can easily establish.

Step 4: Leave space around stems

Don't tightly pack mulch against delicate plant stems or crowns.

Step 5: Water normally

Water can pass through the wool and into the soil below.

Check the soil rather than simply looking at the surface when deciding whether your plants need watering.

Can I just put raw sheep's wool in my garden?

Raw or minimally processed sheep's wool can be used in gardens, but there are a few practical considerations.

Loose wool behaves differently from a manufactured garden mat.

It can move around, may be difficult to apply evenly and its cleanliness and consistency depend heavily on where it came from. People often find it blows in the wind and ends up in the lawnmower. This is annoying. Thats why Sustaina Grow uses matted wool. 

Raw wool also adds viable seeds to your garden from the paddock. That is why we do not recommend using Raw Wool in the garden as you will be introducing a new problem and new weeds to your garden.
Sustaina Grow wool products have NO viable seed in them.
Our products simply turn NZ strong wool into consistent formats that are easier to install and use for particular gardening jobs.

Is wool mulch safe for the garden?

When you're putting anything around food crops, it's reasonable to ask where it came from and how it has been processed.

We recommend using wool products specifically intended for gardening and following the manufacturer's instructions. At Sustaina Grow, we work with 100% New Zealand wool, with our garden products made and hand-packed in Ohakune.

For us, traceability isn't a marketing extra. We're a farming business ourselves, and understanding where the fibre comes from has been part of Sustaina Grow from the beginning.

Frequently asked questions

Can sheep wool be used as mulch?

Yes. Wool can be placed over garden soil to help suppress weeds, retain moisture and protect the soil surface.

Does wool mulch biodegrade?

Yes. Sheep's wool is a natural fibre and gradually breaks down. The rate depends on the product and conditions.

Does water go through wool mulch?

Yes. Rain and irrigation can move through wool mulch into the soil below.

Can I use wool mulch in a vegetable garden?

Yes. Wool mulch can be used around many vegetable and fruit crops. Leave appropriate space around plant stems and crowns.

Is wool good around strawberries?

We think strawberries are particularly well suited to wool mulch because the wool can suppress weeds, cover exposed soil and create separation between fruit and the soil.

Can wool mulch be used around garlic?

Yes. Wool can be used to cover soil around garlic while allowing plants to grow through openings.

Does wool fertilise plants?

Wool contains nutrients including nitrogen and sulphur, which can become part of the soil system as the fibre slowly decomposes. We regard this as a gradual secondary benefit rather than the primary purpose of wool mulch.

How long will wool mulch last?

It varies considerably. Some Sustaina Grow wool garden products can remain useful for approximately 18 months to two years depending on environmental conditions.

What we've learned from working with wool

After years of developing wool garden products, one thing has become clear to us:

Wool doesn't need exaggerated claims to be useful.

It's a natural fibre.

It covers soil.

It can suppress weeds.

It can help retain moisture.

It insulates.

It gradually breaks down.

And New Zealand grows a lot of it.

Our job at Sustaina Grow is to keep finding practical ways to put that fibre to work, and to test those ideas properly rather than simply repeating claims because they sound good.

That's why we'll continue adding our own trials, photographs and results to this guide as we learn more.

If you're experimenting with wool in your own garden, we'd love to see what you're growing too.

About Sustaina Grow

Sustaina Grow is a New Zealand business creating practical gardening products from New Zealand strong wool.

Our products are developed around a simple idea: use a natural material New Zealand already produces to help people succeed at growing.

Explore our wool garden products →