Horticulture Magazine

The Ultimate Guide To Garden Mulching

mulching on garden flowerbed

Many gardeners aren’t aware of the myriad benefits mulching can bring to your garden.

If you’re looking for healthier soil, fewer pests, stronger plants, and a more attractive garden, then mulch could very well be the answer.

After reading you’ll be equipped with the information you need to find and prepare the right mulch for your garden.

What Is Mulch?

gloved hands showing old grass clippings and dead leaves used as mulch

Mulch is a soil covering designed to improve the quality of the soil beneath.

It is layered onto soil or compost: the act of mulching.

There are many types of mulch, each with its own properties, benefits, and potential drawbacks.

The type you choose will depend on your gardening goals.

Mulching Benefits

grass clippings being placed over garlic plants as mulch

Broadly speaking, mulch strengthens the soil around your plants.

Most mulch types keep moisture in your soil and help to reduce the amount of weed growth.

It also protects the roots of your plants during winter, by reducing the frequency and severity of freeze-thaw cycles.

Some types of mulch give nutrients to the soil, which can be useful in replenishing lost nutrients and improving soil fertility, while other types are helpful in discouraging pests.

gardener shown mulching tomato plants with straw

In general, mulched gardens grow healthier than those without mulch.

Mulching your garden also saves time spent watering and weeding: two of the main time-sinks in garden or allotment maintenance.

Depending on the type you choose, it can also make your garden look neater.

Types Of Mulch

Dark red and light brown mulch used in garden

Here’s a list of some common mulch materials:

  • Grass clippings
  • Garden compost
  • Chopped leaves
  • Spent mushroom compost
  • Spent hops
  • Wood chip
  • Processed bark
  • Manure
  • Straw
  • Seaweed
  • Slate
  • Pebbles
  • Chipped stone
  • Aggregates
  • Gravel
  • Seashells
  • River rock
  • Glass
  • Sheets of fabric

As you can see, they fit into two broad buckets: organic and inorganic.

These two categories overlap broadly with biodegradable and non-biodegradable mulches, with a few exceptions (like seashells which are organic but non-biodegradable).

For gardening purposes, it’s most helpful to split mulches out by whether they are biodegradable or non-biodegradable.

Biodegradable Mulch

hands sifting through garden waste

These mulches will break down over time and release their nutrients back into the soil.

This means they’re great for replenishing soil nutrition and boosting fertility.

Biodegradable mulches are good for keeping moisture locked into soil, and for reducing weed levels.

They’re less effective at deterring pests, though.

Non-Biodegradable Mulch

gravel used to cover two ornamental bushes

Because these mulches don’t break down, they won’t have an impact on the nutrition or health of the soil.

They are still able to help with the weeds and moisture levels.

One of the main draws of mulches from this category is that they can be used decoratively, to great effect.

Choosing a mulch based on how it looks rather than how it will benefit your soil opens up a whole new layer of landscape design considerations.

Sheet mulch with holes cut for planting

Sheeting may not seem like mulch in the traditional sense, but technically it is.

Draping a sheet over a new or overgrown flower bed is a great way to nuke the weeds: you can cut holes in the sheet for planting, and cover it with other mulch materials if you find it unsightly.

How To Mulch Your Garden

hand using small hand trowel to shift bark near a hosta plant

Applying mulch is quite a simple job.

You just need to spread it out onto the soil in a layer between two and three inches thick, whilst being careful to avoid:

  • Covering small plants entirely, as this can smother or suffocate them.
  • Piling too much mulch against plants, as they can struggle to grow.
  • Mulching too close to trees: you should not mulch right up to the tree.

Before mulching, pull out any weeds right down to the root – this will stop them from growing underneath the mulch.

hands using bark to mulch around a hosta plant

If you’re using a biodegradable mulch, you’ll need to replace or relayer every year as it begins to break down.

Doing this will ensure that your garden continues to feel the benefits of mulching. Whack the old stuff in the compost if you have one.

Then:

  1. Put mulch out in small piles initially, over the whole area you’re planning to cover. This makes it easier to gauge how much you’ll need.
  2. Rake the piles once they’re out to create even coverage.
  3. Once this is done, water the top layer gently. Enough to dampen it but not so much that you create any puddles, which can damage the mulch and reduce its effectiveness.
Tomatoes grown on a bed of mulch
Make sure you give everything the space it needs to thrive

Mulching will deliver the most benefits if done between mid-spring and autumn.

This is when soil is warm and moist, giving plenty of temperature and moisture for the mulch to lock-in.

Grass

lawn with grass clippings left as mulch

Adding mulch to grass is a great way of reusing waste, whether it’s grass cuttings or fallen leaves.

This is beneficial for your garden, and for reducing pressure on landfill sites.

If the soil under your grass is at least 6°C, then grass or leaf mulch will break down and boost the health of your lawn.

Newly Planted Trees

hands mulching around a newly planted tree

A mulch with medium texture is best for trees.

Fine mulch can compact too tightly and starve the tree of oxygen, whereas coarse mulch does not hold enough water in.

Be aware that mulching too close to a tree can be harmful, as can laying mulch too thickly.

Both of these things can starve the roots of oxygen and stunt the growth of the tree over time.

Perennials

mulch used as a walkway between tall perennial plants

Organic mulch is best for perennials, as it replenishes the soil with the nutrients that they demand year on year.

Other plants can be rotated, or the soil replenished by turning the compost, but the best way for perennials to get this nutrition is from mulch.

A layer of two to three inches deep works best.

Vegetables

straw used excessively on a bed of beetroot plants

If you’re mulching veg, this can be done in winter after planting out.

You’ll want four to six inches of mulch.

Sawdust is popular for vegetable gardens, as are straw and wood chips – these mulches offer good all-round protection for veggies.

Some vegetables are better suited to different types of mulch – tomatoes and other heat-loving plants may want something thicker, for example – so it’s good to understand the needs of your crops.

Mulching Disadvantages

There are a few potential disadvantages to mulching in general, and some individual mulch types have specific disadvantages.

Laying mulch too close to tree stems can make them vulnerable to disease, but following the steps above should ensure this doesn’t happen.

Some mulch mixes can bring weeds into your garden rather than protecting against them.

Weeds poking through mulch

To avoid this happening, make sure you choose high-quality mulch.

As we said earlier, organic mulches won’t protect against pests, and non-biodegradable mulches won’t contribute to soil quality.

It’s worth evaluating the suitability of the type of mulch you’re planning to use, to make sure it’s suitable for your needs.

Mulches with wood, for example, can draw nitrogen from your soil: if you’re using these you’ll need to compensate.

FAQ’s

Here are a few questions we’re often asked about mulching:

Can you put mulch over weeds?

No! You should remove weeds first, including the roots.

Can you put fertiliser over mulch?
watering can used to fertilise heavily mulched tomato plants

Yes. Applying a thin layer on top of the mulch and watering gently will ensure the fertiliser reaches the soil beneath.

Do you have to remove old mulch before putting a new layer down?

Yes. You should only add a new layer of mulch once the previous layer has rotted away completely, otherwise, you risk the mulch layer becoming too thick.

spade moving bark mulch from a large hosta plant

Theoretically you can put a new layer of organic mulch over an old layer of the same type, but we still recommend removing the bottom layer.

Should you water before or after mulching?

Ideally just afterwards, but the soil beneath the mulch needs to be damp. You may need to water it if it’s dry.

That’s It…

gloved hand mulching juniper plants with pine bark

Mulch is an incredibly useful and versatile tool in the gardener’s arsenal.

It has the potential to deliver all sorts of benefits, depending on your needs and the type you use.

This guide introduced the different types of mulch and their top-level benefits.

You should now have everything you need to decide which mulch is best suited to your garden.

Whether you opt for biodegradable or non-biodegradable, mulch is a great way to quickly improve the health and aesthetic appeal of your garden.

Happy gardening!

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