Rock Vs Bark Mulch What’s Best For Your Garden?

Rock vs Mulch

By John Johnston

In this article, from us here at landscape gardeners Glasgow we’re going to talk about rock vs mulch landscaping (mulch, great word, isn’t it?). We’ll explore what it is, how it’s used and the different mulches available.

In particular, we’re going to focus on rock mulch. We’ll see how it can benefit your garden, how you can use it in your landscaping plans, and some of the best plants to grow in it.

What Is Mulch

The word ‘mulch’ describes any material that you lay on top of your soil. This means that there’s no set recipe for it. You can use all kinds of different things to make mulch including garden leaves. Mulching is the process of putting mulch on top of your soil.

Popular mulching materials include anything from traditional garden fare such as compost, leaves and grass cuttings, to more unusual things like shredded newspaper, wool, and seaweed.

Mulches made from different materials have different properties. The main difference between mulches is whether they’re organic or inorganic.

Organic mulches break down into the soil over time. The idea is that the nutrients contained in the mulch will go into the soil beneath, improving its quality.

Inorganic mulches don’t break down but stay where they’ve been laid. They’re used more for decorative purposes than to benefit the soil – although they do have the benefit of suppressing weeds and keeping the soil moist so that plants and trees can thrive.

When it comes to these different types, the most obvious difference is that rock is inorganic and bark organic, but each has its own pros and cons:

Rock Mulch


  • Cost-efficient: lasts longer
  • Wide variety to suit taste, budget, space, etc.
  • Looks attractive
  • Helps prevent weeds
  • Low maintenance


  • Higher initial cost
  • More water needed to reach the soil below
  • Doesn’t add nutrition to the soil
  • When rocks heat up in the sun they can potentially drain moisture from the soil and plants


Bark Mulch


  • Better for the soil
  • Helps prevent weeds
  • Retains soil moisture
  • Helps moderate soil temperature
  • Easy to work with


  • Needs replacing every few years
  • Lack of variety
  • Potential for fungi and mold growth
  • Can be disturbed more easily than rock

Types of Rock Mulch


  • Chips of broken slate are common rock mulch material; particularly when in a deep blue/grey colour. Other kinds include buff-coloured and a river-worn variety known as paddle stone.

River Rock

  • Smooth, river-worn grey stones of the sort you might find on a beach.

Gravel or Cobblestones

  • Both of these are made by crushing rock. Cobblestones are just larger chunks.

Brick Chips

  • Red stone or brown crushed brick mulch can add a vivid, autumn-like contrast to your garden.


  • Bold, rough-edged pieces of rockery stone that you would be more likely to find in larger beds.

Rock mulches also come in different sizes. You’ll have seen landscaped gardens using everything from the smallest pieces of gravel to larger boulders. The size you pick will ultimately depend on everything from your taste to available space. You also have the option of mixing and matching mulches to create contrast. One great thing about stone mulches is that you’re only limited by your imagination.

You Can Use Rock Mulch Just About Anywhere

Using rock as mulch will look good anywhere in your garden. They work particularly well with borders and around tree bases. The low maintenance required makes it really useful for smaller, hard to reach areas. It’s a great choice for driveway areas where you might want a small plant or bush feature.

Another place it’s handy is high traffic areas. For example, if there’s a part of your garden that people tend to walk on or take shortcuts over, then this type of mulch is ideal.

Prepare The Ground Area

When getting ready to put your rock mulch down, there are some steps you can take to head off potential problems.

Once you’ve cleared the soil of weeds and debris, you’ll want to make sure that the area is sufficient depth for mulching. Check out our post on The Top 10 Essential Gardening Tools For Beginners to help you with this. If you’re using lightweight mulch such as gravel and the area isn’t deep enough, there’s the possibility of bare patches once the wind starts blowing the top layer around. Generally, allow a depth of two inches.

You then have two options: Some garden designers like to place a layer of organic below the rock, particularly if they’re growing plants or trees. This is easy enough to do and keeps the soil happy but does have its drawbacks: Extra cost aside, an obvious disadvantage is that, if you ever want to replenish the organic mulch, you have to remove the rock first. One way of mitigating this issue is to use compost which decomposes more slowly, such as bark.

Another weed-preventing option is to lay a sheet of weed barrier fabric beneath the mulch. This material is designed to let water and air get to the soil, whilst also blocking sunlight and so suppressing weed growth. One disadvantage of this is that plants can’t grow through it. However, if you’re not planning on growing anything in that area, this can be an effective method of keeping it free of weeds.

Maintenance Requirements

Besides looks, one of the main reasons people go for rock mulch is because it’s low maintenance. However, there are a few things you can do to keep your beds and borders looking pristine. Even weed barrier fabric will deteriorate over time, especially if laid underneath the rough stone. Once it begins spitting, weeds grow through. It’s a good idea to keep an eye on the fabric and replace it when it becomes damaged.

Weeds don’t necessarily need soil to grow. A lot of weed seeds can be carried around in the air. If they land in accumulated grime between the stones they’ll begin to grow. Getting rid of weeds as soon as they appear will prevent them from becoming established.

The Best Plants For Rock Mulch Beds

There are many plants that can thrive in stone mulch; it’s simply a case of knowing what they are and how to look after them. Rock plants – or to give them their proper name lithophytes, are pretty well explained by their name. Some can grow purely on a rock, or among them. Succulent plants are also excellent for growing in rock. They’re so-called because they maintain water, which is essential if they’re growing around rock which can heat up in the sun.

Another great plant for rock beds is alpine plants. These are plants that can withstand harsh conditions and, like rock mulch, require little maintenance.

Pasque Flower (Pulsatilla Vulgaris)

  • Is a herbaceous perennial which grows in clumps. Importantly for rock gardens, it’s drought-tolerant, meaning that it can survive with relatively little water. Its flowers are purple and cup or bell-shaped.

Pinks (Dianthus Chinesis)

  • Pinks are hardy perennials similar to carnations. They can grow in less aerated soil than other plants, meaning that they don’t need as much water, air or nutrients to grow.

Bellflowers (Campanula)

  • Grow like a carpet and so are ideal for borders. They come in hundreds of varieties. The alpine types tend to have blue or white-and-purple flowers.

English Stonecrop (Sedum Anglicum)

  • One of the more common succulent plants found in the UK. Again, it’s an ideal border or rock garden flower as it’s low growing and mat-forming. Its flowers are pink-tinged.

Kotschy’s Crocus (Crocus Kotschyanus)

  • Best planted in large groups, Kotschy’s Crocus is an award-winning autumn flower. It has lilac-and-pink flowers with a yellow centre.

Variegatum (Sedum Kamtschaticum)

  • It is a succulent plant with fleshy, spoon-shaped leaves with golden edging. Its flowers are star-shaped.

Boughton Silver (Hebe Recurve)

A shrub is suitable for borders. Its foliage is silver-blue and it blooms with small, white flowers.

Heavenly Blue (Lithodora Diffusa)

  • Belongs to a group of plants known as sub-shrubs – shrubs that aren’t very large. An evergreen favourite for rock gardens, it produces deep blue flowers.

Tumbling Waters (Saxifraga Longifolia)

  • An alpine plant that forms a mat between and over rocks. It’s an evergreen with strap-shaped leaves and white flowers.

Hinoki Cypress (Chamaecyparis Obtuse Nana)

A conifer that prefers acid soils and can grow in winter temperature. It’s low maintenance and easiness to grow makes it a popular rockery plant, especially for beginners.



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