What Is Mulch? | Types Of Mulch And When To Use It

Welcome to my WTF Gardening series, where I take common gardening terms and explain them for those who are new to the world of plants. Find the entire WTF Gardening series here.

Mulch sounds a bit like a blend of two words (maybe ‘mud’ and ‘squelch’?), and you’ve probably heard it uttered by a few television gardeners, but you’re not quite sure what it is. Let me clear it up for you.

Mulch is commonly used in outdoor gardening. It’s a material or mix of materials that is spread on top of soil as a covering.

A few reasons why you might use mulch

Retain moisture in the soil
Keep the soil and plant roots cool
Stop weeds growing growing
Improve fertility
Make your garden more visually appealing

Types of mulch

There are two types of mulch commonly used by gardeners: organic and inorganic. Within these, there are lots of different materials that can be used as mulch, most of which can be found at your local DIY store or garden centre. You may even have them already at home.

: Manure

: Straw

: Bark

Some types of organic mulch materials include:

Compost
Bark
Grass cuttings
Composted manure
Newspaper
Shredded Leaves
Straw

If your main aim for mulch is to fertilise your plants, then organic mulch is the way to go. A drier or woodier mulch such as bark will take longer to decompose and provide less nutrients to your soil – but it might look nicer.

Note that organic mulch will eventually decompose and will need replacing more often than inorganic mulch. This may not be the way to go if you’re a lazy gardener!

: Recycled glass

: Gravel

Some types of inorganic mulch materials include:

Gravel
Recycled glass
Rubber
Landscape fabric

As I mentioned, organic mulches need replacing regularly, whereas most inorganic mulches don’t, because they don’t decompose anywhere near as fast.

The mulches listed above are excellent weed blockers, and they’re generally better at holding in moisture; however, there is some controversy surrounding the impact that these mulches can have on plant life and wildlife. For example, some of rubber tyres (which are sometimes recycled for use in rubber mulch) contain zinc, and excessive zinc can be harmful to plants.

Vegan mulch

For those who live a vegan lifestyle or who are concerned about the environment and wildlife, there is also the option of vegan mulch. So what makes mulch vegan? It’s the fact that it’s free from peat.

Peat comes from peat bogs. It is composed mainly of wetland vegetation: principally bog plants including mosses, sedges, and shrubs. Peat only forms a layer of around 1mm per year. A 10 metre deep peat bed takes 9,000 years to form!

The mining of peat bogs has a very negative direct impact on the environment. This is because peat bogs are home to plant and wildlife species which can only exist in this unique environment. Peat bogs are also Sites of Special Scientific Interest (SSSIs) but, alarmingly, only a small number of the remaining peat bogs in the UK are protected against mining.

Peat alternatives use materials such as green compost, coir, wood fibre and composted bark. Remember: just because a compost is labelled ‘organic’, doesn’t mean it’s peat-free. You should always read the packet to check!

When to use mulch

Seedlings

Mid to late spring is the best time to lay down mulch before the growing season. This will give your soil a chance to warm up and melt away any frosts that may be lingering.

Lay down a thin layer of mulch at first – around 1 to 2 inches. This will allow seedlings to get through. You can always lay down more mulch once plants have established if you need to!

If you already have a layer of mulch on your plants (for example, if you’ve moved into a new house and you’re taking over the garden) make sure to remove it gradually as winter turns into spring. Removing it all at once runs the risk of exposing your plants to a last minute frost and possibly killing them.

Winter mulch

The other important time of the year to consider spreading mulch over your soil is in the winter. The climate can fluctuate unexpectedly in winter, and protecting your plants from constantly freezing and thawing is important for maintaining dormancy. Why? Because if your plant believes it’s coming out of dormancy, but gets hit by another frost, it can cause dieback and affect the health of the plant.

To protect your plants (especially newly planted perennials), apply mulch after the first frost, making sure to remove any leftover spring mulch beforehand. Dry twigs or bracken are excellent mulching ingredients in this case, and a 2 to 4-inch layer around the base of the plants will help to regulate the temperature and keep your plants happy!

So there you have it – mulch, explained in a nutshell! What would you like to see me cover next in my WTF Gardening series? Let me know in the comments section!

Mr Plant Geek

Michael has been involved with gardening and plants since he was just five years old. He is a self-professed Plant Geek, and was listed in the Sunday Times top 20 most influential people in the gardening world, thanks to his plant hunter role at Thompson & Morgan.

Michael was responsible for new plant introductions such as the Egg and Chips plant and the FuchsiaBerry and keeps busy travelling the world in search of new plants as well as lecturing worldwide, including stints in Japan. He is very active on social media – so why not give him a follow at @mr_plantgeek or Facebook – and writes a plant-focused Substack called Grow This, Not That.