A Guide to Building Rock Gardens

how to build rock gardens

The Spruce.

Rock Gardens for Small Spaces

Small rock garden full of plants.

David Beaulieu

Some homeowners design rock gardens to exploit rocky slopes that constitute problem areas in their yards. Others import rocks into yards that are flat and that lack rocks. In the latter case, stronger backs are required, but the effort is well worth it.

Another consideration that can influence the design of rock gardens is space. The project illustrated below was undertaken in a small space. In larger spaces, the goal is often to create sprawling, naturalistic rock gardens.

But those with small yards will want to content themselves with what amounts to a round raised bed made of select rocks. This design can fit neatly into a well-chosen nook. The small rock garden will not be in the way when you mow your lawn, nor will it require much maintenance.

Yet a third design consideration is colour. Use red sandstone to provide a structure for your rock garden that is attractive, as well as functional. Wash the dirt off the sandstone to bring out the red colour to maximum effect.

In turn, the choice of stone influences plant selection. Use a colour scheme that will work well with the red sandstone. You want some plants with a hint of red in them, but also some plants displaying silver, yellow, and white.

Sandstone is hardly the most durable of materials. It crumbles over time and always seems to be on its way to becoming soil. But beauty is the goal of this project, not longevity. If you want longevity, choose a stone such as granite.

The only supplies needed for the project are:

    • Stones
    • Plants
    • Trowel, shovel
    • Wheelbarrow (to move soil and compost)
    • Tape measure

Rock gardens normally achieve some elevation above the surrounding ground. In this case, that means laying a first course of rocks and soil, then building upon it.

The First Course

First course of a small, circular rock garden.

David Beaulieu

If are building your rock garden on a patch of ground currently covered with grass, decide how you will deal with the grass. You do not want grass shoots popping up in and around your rock garden afterward. You could dig up the grass before beginning, but an easier way is to lay down a layer of newspapers and shovel dirt on top of them to hold them down.

The layer of newspapers will eventually smother the grass, which will then begin to decompose. But even before decomposition takes place, you have accomplished the first task for the project: furnishing a clean slate upon which to work.

If you have an area already cleared, you can skip the task of laying newspapers and proceed to the next step, which is to lay the first course of stones and soil.

Lay out a circle of rocks as the perimeter of your base. Make the diameter of the base about 4 feet. Do not use any rocks larger than 12 inches in any dimension (so that they are not too tough to manipulate), but do use up most of your largest, least attractive rocks in this bottom layer (so that you do not have to lift them).

With the circle of stones in place, it is time to fill it with soil. Rock gardens, as a rule, are composed of plants that require a type of soil that provides good drainage. This means using sandy soil. If all you have is a clayey soil, add sand and compost to it to promote better drainage. Once shovelled into place, walk on the soil to pack it down.

Later, as a complement to your sandy soil, you will install plants that are traditionally used in rock gardens and that like good drainage.

The Second Course

Second course of a small, circular rock garden.

David Beaulieu

The second course of the raised-bed rock garden is simply a smaller version of the first. The diameter of the stone perimeter that you lay on top of the first layer will be smaller, forming a circle within a circle.

In laying this second course of stones for the rock garden, make the circle small enough that plenty of room for planting is left over around the perimeter of the first layer. Along with the space available within the second layer (in between the stones), itself, this will be where you install plants later.

Since you used your heaviest stones for the first course, you have lighter, more easily maneuvered stones to use for the second course. It is all right to reserve one or two large rocks for the second course if they are especially pretty. That is because the rocks of the second course will show up more, being closer to the eye.

Selecting Plants for Rock Gardens

Purple wood spurge plant in bloom.

David Beaulieu

Although on an ideal level, plant selection would be driven purely by colour scheme, practical considerations often get in the way of our choices. The use of colour schemes in landscaping projects differs markedly from their use in, say, painting, in at least one important respect. And that is that plants, as living things, have growing requirements to take into consideration. So, adherence to colour schemes in landscaping can never be as single-minded as it can be in the art world.

We have already looked at one growing requirement: drainage. Seek specimens that will grow best when water percolates readily through their soil. It would be a mistake to add a plant that prefers wet soil to this mix, no matter how much it does for the colour scheme. Only plants with similar growing requirements should be grouped together unless you are willing to sacrifice longevity for a temporary pop.

Besides drainage, other considerations are light requirements and amount of water needed. If you have a sunny area, select plants that thrive in full sun, making them compatible both with each other and with the spot chosen for the rock garden. Drought-resistant plants are best, although you can make an exception for a particularly handsome specimen that you can treat as an annual (and, therefore, a temporary) plant.

Also, seek variation in plant height and leaf texture.

To summarize, before going to the nursery to buy rock-garden plants, make the following list of criteria for plant selection. Each plant should:

    • Fit into the desired colour scheme
    • Prefer good drainage
    • Need only a moderate amount of water
    • Prefer a sunny area
    • Show some variation in height and texture

Plant Choices for This Rock Garden Project

New snow-in-summer plant in rock garden.

David Beaulieu

It is tempting when shopping at the nursery to select a wide variety of plants. Resist this temptation! Succumbing to it will lead to a hodge-podge, rather than a unified look. For the sake of your design, stick to a colour scheme. Also, too many different kinds of plants will make the space look too busy; two different kinds of plants of each desired colour is plenty for this small space. Repetition of the same plant-type promotes unity.

To achieve a unified look with your plant selection, buy:

As the years go by and the daffodil and lamb’s ear spread, divide them. If you decide that they clutter up your rock garden too much, transplant them to somewhere else in the yard.

The Colour Scheme

Scotch moss plant growing in rock garden.

David Beaulieu

Here’s a closer look at the plants selected (and the reasons that they were selected):

    • Scotch moss (Sagina subulata Aurea) gives us a short plant with a touch of yellow.
    • Daffodil (Narcissus) offers more yellow. This particular daffodil is a miniature suitable for small rock gardens.
    • Wood spurge (Euphorbia amygdaloides Purpurea) provides yellow (its blooms) and red (its stems). It’s a taller plant than the rest, giving the composition some depth.
    • Offering more red color is the foliage of low-growing hens and chicks (Sempervivum tectorum).
    • Low-growing snow-in-summer (Cerastium tomentosum) gives us silver (its foliage) and, later, white (its blooms).
    • The taller lamb’s ear (Stachys byzantina) offers more silver foliage.
    • The most striking white is provided by the flowers of candytuft (Iberis sempervirens Purity).

Focus on foliage in your rock garden design. Flowers come and go, but foliage serves as a backbone for a composition. Even so, this rock garden will look nicer in spring and early summer, when the plants are in bloom than it will in late summer. That’s a compromise you must make unless you have a space large enough to implement a sequence-of-bloom agenda. For colourful blooms throughout the summer, you can easily add the annual, portulaca, to the mix.

Another compromise made was in using Scotch moss, which is not drought-tolerant. This was a case of sacrificing longevity for a temporary pop. This plant (suited to planting zones 4 to 9) bears small white flowers, but it is grown mainly for the solid carpet of yellowish-green that it provides. Grow it in full sun to part shade. It is very much like Irish moss, except that the latter is a deep green colour.

The only plant in the rock garden grown more for its flower than its foliage is the daffodil. The relatively coarse textures of the lamb’s ear, wood spurge, and hens and chicks contrast well with the other plants, all of which have a more delicate foliage.

Planting the Rock Garden

Candytuft's bloom with its interesting petal pattern.

David Beaulieu

In deciding where to begin planting (and with which plants), think in terms of planting in threes (three of the same kind of plant). The white blooms of candytuft will be one of the rock garden’s most striking features, so plant the three candytufts first, selecting spots for them where their dazzlingly white flowers will really pop. For example, one of your nicer sandstones would make a great background for candytuft flowers. You now have a triangle of white that anchors the composition. The rest of the plants will radiate out from each point in the triangle.

Inserting Additional Rocks

Small, light-red rock in a rock garden.

David Beaulieu

As you plant, add more rocks. Since this is a rock garden, the look you’re after is a mass of rocks with plants popping out between the cracks. But if all of the rocks were laid at once, they’d be in the way of the plantings.

So, instead, additional rocks (mainly small ones) are inserted as the planting proceeds. Install a plant somewhere first, then create the “cracks” around it afterward. It’s a lot easier to change your mind and move a small rock to another position than it is to dig up plants and replant them somewhere else.

There’s a delicate balance to pursue between the planting and the rock installation, but your goal ultimately is to cover as much of the surface as possible with rocks and plants. The process is rather like putting together a jigsaw puzzle, except that you determine how the puzzle turns out.

Mulch for Rock Gardens

Rocks used as mulch in a rock garden.

David Beaulieu

Mulching can present a dilemma for the novice in rock gardening. On the one hand, you want to suppress weeds in the rock garden, but, on the other hand, the widely used bark mulches would look out of place in rock gardens. So, what do you use for mulch?

The answer is stone. But not just any stone. Strive for a stone mulch whose colour will fit with the colour of your main rocks (in this case, red). Make sure you have a range of sandstone rock at your disposal, from the large rocks that formed the circles to smaller stones to pebbles. The latter will make the perfect mulch. You can also buy red stone mulch from a home improvement store (although the colour is unlikely to be a perfect match).

By David Beaulieu