Mulching: Why? How?

What is mulching used for?

Covering bare soil surfaces (between plants in flower beds, at the base of trees and shrubs…) with mulch helps to:

• Reduce erosion on the surface, caused by rain and wind, which leads to the formation of a crust on top of the soil. This crust, sometimes called a “surface crust”, hinders water penetration.
• Slow the growth of “weeds”, particularly annuals that cannot germinate without light under the mulch layer… It’s even more effective if you take care to clear the surface before spreading the mulch!
• Limit evaporation on the surface during dry periods and, conversely, retain moisture in the soil. This helps save water in summer and reduces the frequency of watering!
• Act as an insulating “mattress” or “duvet” on the soil surface, protecting plant roots from summer heat and winter cold.
• Depending on the material used, such as green waste (prunings, grass clippings, dead leaves), the mulch, as it gradually decomposes, can also enrich the soil with nutrients.
• Give your garden a polished finish or even a “decorative” touch if you combine different mulches or opt for coloured mulches.

There are essentially two types of mulch: organic mulches and mineral-based mulches.

A pile of shredded pruning material – Heat release is often observed… This is generally healthy as it eliminates potential diseases, but remember to clear plant crowns properly when applying mulch.

The main organic mulches available commercially

Pine bark, hemp or flax mulch, wood chips… organic mulches come in a wide variety. You can easily find the following in stores:

• Pine bark
  Pine bark is commonly available in different sizes, either bagged or in bulk. It’s a long-lasting mulch as it decomposes slowly. Additionally, it has an acidifying effect on the soil over time, making it ideal for heathland trees and shrubs that thrive in acidic soils. It can also be used to cover non-cultivated areas like pathways.

⇒ Pine bark: uses, advantages and disadvantages

• Hemp mulch, flax mulch and miscanthus mulch
  Hemp, flax and miscanthus mulches are popular for their light colour, which highlights plants in flower beds. These neutral, lightweight mulches spread easily but decompose relatively quickly, within about two years. They are usually sold in bags and are particularly well-suited for mulching around perennials, annuals and small vegetable gardens. At the end of their lifespan, they can be simply raked into the soil.

• Wheat straw
  This is the “original” material, traditionally used in vegetable gardens and to protect tender plants in winter. It’s quite hard to find in stores but easier to source in rural areas. However, if it comes from a nearby farm, it’s more likely to be sold in round bales rather than small bundles. Economical and quick to decompose, straw is perfect for vegetable gardens, though it’s not very dense and may allow weeds to grow through if not spread thickly enough. When pre-shredded, it becomes much more effective for ground cover. In the garden, you can use it to mulch flower beds and around trees and shrubs. Stylistically, it has an undeniably “rustic” look – charming in natural gardens but perhaps less so in contemporary spaces.

• Wood chips and wood shavings
  These two materials differ in size: wood chips are finer, while wood shavings are coarser. They are by-products from sawmills, made from hardwood or softwood, and are sometimes available in dyed versions using water-based colourants. Wood chips are lightweight and break down quickly, whereas shavings last longer. They can be purchased bagged or in bulk. Note that many tree surgeons now shred their waste on-site – don’t hesitate to contact them, as they may offer large volumes of shredded wood or wood shavings at reasonable prices. Wood chips are mainly used in perennial beds, while shavings are more versatile and can also mulch around hedges or trees.

• Coconut husks
  Coconut husks are a by-product of the food industry. They come in small 1-2 cm pieces, which are quite heavy and dense. This mulch doesn’t blow away, decomposes very slowly and doesn’t mould. Its dark brown colour makes it highly decorative, well-suited to Mediterranean plants and garden pathways.

• Cocoa shells
  Cocoa shells come from the husks that encase cocoa beans – they even have a distinctive smell! Neutral in pH, this mulch typically decomposes within a year, enriching the soil. It’s mainly used for flower beds and borders. However, it’s not recommended if you have a dog prone to nibbling things, as it contains theobromine, a plant alkaloid toxic to canines.

• Buckwheat hulls
  Buckwheat hulls are among the finest mulches. They’re relatively easy to find in western regions, particularly among pancake enthusiasts! With their attractive glossy brown colour, this mulch is perfect for pots and small, well-tended flower beds. It’s also used in vegetable gardens as slugs reportedly struggle to move across it. It gradually breaks down over two to three years and can be worked into the soil.

The range of mulches is constantly evolving. You can also find unique natural mulches like apricot, peach or hazelnut shells available online.

Pine bark, wood chips, miscanthus mulch and buckwheat hulls: organic mulches

→ Discover all our organic mulches

Garden waste mulches or mulch

Buying mulch is convenient but relatively expensive. The most economical and natural solution is to use your garden’s plant waste for mulching. Almost everything can be turned into mulch.

• Grass clippings
  Once dried in the sun, grass clippings are ideal for mulching vegetable patches. They decompose quickly and provide nitrogen to plants, which is particularly beneficial in spring. However, avoid spreading wet grass in thick layers: it would form a compact, slimy, and foul-smelling mass. This fermentation is not good for plants! If you can’t wait for the grass to dry, spread it in thin successive layers.

• Shrub prunings
  Hedge trimming often generates a lot of waste. Instead of disposing of it, shred it! Depending on the season, you’ll get slightly different mulch. If you prune deciduous shrubs in winter, you’ll obtain dry mulch that lasts several years. If you prune evergreen shrubs or deciduous shrubs in late spring or summer while they’re in leaf, you’ll get greener mulch: this is Ramial Chipped Wood (BRF), an excellent mulching material!
  → Read more on the topic: “What is BRF? How to use it in the garden” and “Garden shredders: uses, different models, and how to choose”

• Perennial and annual plant trimmings
  When cutting back your annuals, perennials, and ornamental grasses in autumn or spring, you can simply leave the trimmings in place. To improve their appearance, roughly chop them with secateurs or spread them out and mow over them. These trimmings will decompose quickly and form excellent maintenance mulch.
• Dead leaves
  They are a precious resource in the garden—it would be a shame to waste them by taking them to the tip! Spread them in autumn, of course; they make excellent mulch for flower beds, around trees, and in vegetable patches. To learn all about using dead leaves in the garden, check out our guide: “Dead leaves: how to use them in the garden” as well as Olivier’s video on the subject: How to use dead leaves – Video tutorial
• Garden compost
  Coarse, partially decomposed compost can be spread as a nutrient-rich mulch: it will finish decomposing on the soil surface and nourish the earth in one go.

Mineral mulches, a special case

Mineral mulches are most often made up of gravel, pebbles, crushed slate or even pumice stone.

Decorative and popular in small gardens and contemporary flower beds, they help suppress weeds and retain some soil moisture in summer. However, being inert, they don’t nourish the soil like organic mulches would.

They are particularly recommended in specific situations:

• In rock gardens or trough gardens, to protect alpine plant crowns from winter moisture while keeping roots cool in summer,
• In Mediterranean gardens where adapted plants prefer dry, poor soils,
• For creating gravel gardens or recreating limestone-type environments.

Pumice stone, gravel, slate mulch and clay pebbles

Note that landscape fabrics used in some landscaping projects are sometimes referred to as mulching mats. While increasingly used in gardens, they aren’t particularly attractive. For more information, see our article: “Landscape fabric: pros and cons”

→ Discover our full range of mineral mulches

What is the best mulch?

We are often asked what the best mulch is. It’s quite simple: the best mulch is the right mulch for the job. When choosing a mulch, you need to consider two essential criteria:

• the needs of the plants,
• the lifespan of the mulch.

1) Choosing mulch based on plants

Indeed, not all plants have the same needs, so it’s important to select a suitable mulch. Some plants thrive in moist, humus-rich soils, while others prefer dry, poor soils. Similarly, acid-loving plants such as Rhododendrons, Hydrangeas, and small berries… flourish in acidic soil. Others, like Phlomis, tolerate or even appreciate chalky soils. For the former, a mulch like pine bark is perfect. Nutrient-rich mulches that decompose quickly are also a good choice for plants that prefer fertile soils. Conversely, drought-tolerant and heat-loving plants will do well with mineral mulch.

These two borders with similar colour schemes have different needs: the first will benefit from moisture-retentive mulch, while the second will prefer mineral mulch.

2) Choosing mulch based on its lifespan

The lifespan of the mulch also matters: you wouldn’t mulch the base of a hedge with the same materials as vegetable garden rows. For trees and shrubs, opt for a coarse, long-lasting mulch like wood chips—you’ll be set for several years. For flower beds, a finer mulch such as homemade wood chips, flax straw, or miscanthus is very attractive. Finally, in the vegetable garden, dried grass and fallen leaves are ideal as they nourish the soil life and “melt” like snow in the sun, leaving plots almost ready for planting in spring.

For mulching a path or the base of a hedge, choose a long-lasting mulch. Conversely, in the vegetable garden, opt for a mulch that decomposes quickly and enriches the soil.

⇒ Also read our advice: Which mulch for the vegetable garden?

When and how to mulch?

1) When to mulch?

Mulching can be practised all year round. When creating a flower bed or planting a hedge, mulch immediately after planting to prevent weeds from taking hold (this happens very quickly). However, the two most favourable times for mulching are spring and autumn.

• Spring mulching:

Its main purpose is to save water by retaining soil moisture and to limit weeding by suppressing weed growth. It is best carried out between mid-April and mid-May, when the soil has already warmed up slightly but has not yet suffered from drought. You can then top up the mulch layer during the summer.

• Autumn mulching:

Autumn mulching is done before the first frosts, around mid-autumn, for example when tidying up flower beds at the end of the season. Applied before winter, mulch still helps prevent weed growth, but its main role in winter is to form an insulating layer that protects roots from the cold. It also helps protect less hardy plants. A thick layer of straw or dead leaves is perfect in this case.

Also read: Which mulch to choose to protect plants from the cold?

2) How to mulch?

Mulching is a simple operation, but a few precautions are necessary:

• Before mulching, start by thoroughly cleaning your flower bed or vegetable patch, hoe, then water if the soil is dry. Then spread the material on the soil surface between plants, making sure to leave the plant crowns and stem bases uncovered.
• The ideal thickness is generally between 5 and 7 centimetres. 5 centimetres is the minimum for mulch to be fully effective. Note that the coarser the mulch, the more generously you can apply it. Similarly, if your mulch is intended to protect less hardy plants, don’t hesitate: the thicker the layer, the better protected the roots will be – you can double the usual 5 to 7 centimetre thickness.
• If your mulch consists of “fresh” materials like grass clippings, apply it in several thin layers.
• If using fresh wood chips, be particularly careful: spread too thickly, they can generate heat. Keeping shrub crowns uncovered, at least initially, is very important.
• Never mulch dry soil, as this would further hinder water penetration. During dry spells, give the soil a thorough watering before applying mulch.
• Do not mulch frozen ground, as this would have the opposite effect of what you want… trapping the cold in the soil!

→ Also read: How to properly apply mulch

7 Frequently Asked Questions About Mulching

• Should mulch be removed?

Removing mulch is generally unnecessary except in the vegetable garden.

In flower beds, at the base of hedges or trees, simply add a new layer of mulch to refresh it. If you usually work the soil a little in spring and have used an organic mulch that has decomposed well, you can incorporate this organic matter into the soil by lightly raking it in before spreading a new layer of mulch. Otherwise, don’t dig it in but remove the mulch layer and add it to your compost heap where it will finish decomposing.

In the vegetable garden, if mulch remains on the plots at the start of the season (February, March), it’s advisable to remove it so the soil can “dry out” – meaning it dries slightly and can be worked easily and safely before sowing. Removing the mulch will also allow the soil to warm up more quickly during the first sunny days. Excess mulch can be added to compost or used to mulch a flower bed.

• They say mulching causes leaves to yellow, is this true?

Yes, this can occasionally happen but it’s quite rare and only affects young plants. This phenomenon is called “nitrogen hunger”. It occurs if you incorporate poorly decomposed material because, in the soil, microorganisms will use the soil’s nitrogen for this decomposition. It can also happen if you use a carbon-rich mulch (made from woody materials like wood chips or shredded dry branches). It’s very easy to avoid nitrogen hunger by spreading a layer of mature compost at the base of plants just before mulching.
→ Read more: “Nitrogen hunger: what is it? How to avoid and remedy it?”

• The mulch in my flower beds doesn’t stay in place and ends up on the grass, what can I do?

Some lightweight materials like wood chips or flax or hemp shavings tend to blow away at the slightest breeze. To prevent this, water the mulch immediately after spreading to “settle” it. Another trick is, when creating the flower bed, to dig the planting area 10 cm below the lawn level. Cut clean edges: once the soil is mulched, everything will be at the same level and the mulch won’t slide onto the lawn!

• Mushrooms are growing in my mulch, is this normal?

Yes, it’s completely normal and neither dangerous nor concerning: it’s proof that life is developing in and on your soil.

• I used to mulch my vegetable garden but a friend told me it attracts slugs and voles…

Mulching does have this reputation. However, this isn’t entirely accurate. In reality, slugs are more visible when there’s mulch because they shelter in it. But they’re just as numerous, just less visible in unmulched plots as they take refuge in the soil instead. It’s also worth knowing that mulches create a favourable environment for slug predators: rove beetles that devour their eggs. Mulching would therefore rather promote a balance in slug populations.

As for rodents, yes, mulch does favour them if they were already present in the garden. Instead of “bulky” materials like straw, opt for finer mulches or spread them in thin layers.

• Blackbirds keep turning over and scattering my mulch, what can I do?

Indeed, this is one of their favourite activities in winter and early spring… You could try using a scare device but they’re clever and ultimately cause little damage. Besides, like with mushrooms, their presence is a good sign: it proves there are earthworms under the mulch! An occasional light raking will quickly tidy up your flower beds.

• I spread gravel in my small Mediterranean garden but it keeps mixing with the soil…

This is one of the drawbacks of this type of mulch. The ideal solution with mineral mulches is to place a geotextile membrane between the soil and the mulch to prevent the layers from mixing.

To go further

Discover:

• Our advice sheet on decorative mulches: they add style to the garden
• Our advice sheet: Which mulch for a slope or an inclined flower bed?