Looking for your next green-fingered projects? Rock gardens are easy to make, simple to look after and the perfect way to grow pretty miniature alpine plants. An expert at Kew Gardens explains how to get started.
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If you’re a fan of pretty, colourful plants that don’t require a lot of work to look after, then creating a rockery (or a rock garden as it’s referred to in the horticultural world) could be just the green-fingered project you’ve been looking for.
Rock gardens mimic the high-altitude, rugged surroundings where alpine plants are usually found in the wild and, as long as you have a spare patch of soil in your garden or an old planter hanging around, they’re easy to create at home.
“Alpine plants are absolutely tied to their landscape, which are stunning, wild environments and some of the last refugia in the world,” says Tom Freeth, Kew Garden’s rock garden, alpine and aquatics supervisor. “The brilliant thing about recreating these miniature mountain landscapes is that it connects you to that breathtaking wilderness.”
“True alpines live at the top of mountains because they are perfectly adapted to these really harsh, fragile environments,” says Tom. “As the climate warms, less specialised plants start to move up to cooler mountainous reaches, so the area for specialised plants gets smaller and smaller. Growing rock gardens is a good way to raise awareness of the threats these environments are facing.”
Here, Tom has shared his expert advice for creating miniature versions of these breathtaking, delicate landscapes at home.
Where is the best place to make a rock garden?
There are two ways to build a rock garden. If you have outside space with a decent-sized patch of soil, this should provide a good spot to build up a rock landscape. Try to pick a place that’s bright and not shaded by overhanging trees or foliage.
If you don’t have access to outdoor space, you can also create miniature rock landscapes in containers, such as troughs and pots.
“Most rock garden plants will grow really nicely in a container,” says Tom. “But, unlike houseplants, they won’t do well in the warmth indoors. It’s important to place your container on a balcony, use a window box or even put your mini garden on a cold window sill.”
When should you plant a rock garden?
Tom advises planting rock gardens in early autumn, particularly if you’re growing it outdoors.
“The very end of August is absolutely the best time to plant,” says Tom. “The temperature will start to come down and not get any hotter, which means new plants will emerge as it gradually starts to get cooler.”
As the weather gets cooler the plants will start to grow more slowly, so planting in autumn allows them time to send out new roots and make new leaves before the winter. “They can go to sleep over winter and then in spring, when it warms up again, they’re established,” says Tom.
Which plants work best in a rock garden?
Alpine plants, which grow in high mountainous regions in the wild and are naturally hardy, are the most suited to rock gardens. Most of these are pretty, small plants and include things like succulents.
“Succulent alpines are miniature, easy to grow and make really beautiful rosettes,” says Tom, who recommends a species called sempervivum for new rock gardeners. “There’s a huge variety of sempervivum, they look good all year round, there are no conservation issues with them and they’re bombproof,” he says.
You can also easily share sempervivum with your friends. “They propagate as they grow to form smaller plants at the side,” explains Tom. “All you need to do is separate one of those babies, plonk it in another patch of soil and it will root and grow into a new plant.”
Tom also recommends saxifraga for newbie rock gardeners. “These need a little bit more care as they’re less drought-resistant, but they’re still really hardy and are beautiful alpine plants.”
“There are lots of great alpine nurseries out there, many of which are family-run, who can also recommend the best plants to grow for your space and love to hear from people,” Tom adds.
What you’ll need to make a rock garden
- A pot or container (if you’re not making your garden outdoors)
- Stones or rocks – try to use local or salvaged stone where possible
- Crocks (shards of rocks or crockery)
- Peat-free sandy compost
- Alpine plants
- Tools, including a spade and a trowel
How to make a rock garden
Making an outdoor rock garden:
1) Start by weeding and clearing the patch of land you’ve earmarked for your rock garden. “Then make a mound with the native soil,” says Tom.
2) Place down some rubble or crocks (bits of broken ballast) to aid drainage. Top this with a layer of turf, permeable plastic or landscaping fabric that will allow water through it.
3) Choose a nice set of rocks that will give you an attractive landscape and arrange them over the soil. The rocks can be as big or as small as you like, but it’s important to think about logistics before placing your rocks down. “If you can handle all the rocks by hand, it will be a simple process,” says Tom. “If your ambitions are bigger then you might need reinforcements, like a crowbar, to help you get them in there.” Make sure the rocks are firmly placed in the soil.
4) Top the area around the rocks with gritty, peat-free compost.
5) Then it’s time to plant the rock garden. Remove the plants from their pots and plant them into the compost.
6) Dress any areas of bare soil in 12 to 18 inches of grit or pumice. Grit retains water and prevents weeds from growing up.
If you’re making a container rock garden:
1) Choose a container with drainage holes. Place wire or plastic netting over the drainage holes and then cover the bottom with crocks.
2) Fill half the container with gritty compost, leaving space at the top for a thick layer of grit.
3) Arrange your rocks on top of the compost.
4) Plant your chosen foliage around the rocks.
5) Fill up the rest of the container with a thick layer of grit.
How to take care of your rock garden
“It’s all about establishment,” says Tom, explaining that once a rock garden has established its roots it can grow for 20 to 40 years outside.
The plants should be fully established and start to look their best after three years. “It’s a long-term commitment,” says Tom, “but it’s going to provide you years of hassle-free enjoyment.”
When the plants are young they will need a bit of extra mollycoddling, especially if you’re growing them in a container. Getting the watering cycle right at this stage is crucial.
“Find a way to figure out when the rock garden needs watering, whether that’s by sticking your finger in the soil to see if it feels wet and cold or dry, or by picking it up to feel the weight,” says Tom.
How to water your rock garden
“When you water, you want to completely flood the garden and then allow it to dry,” says Tom. However, it’s important not to do this too often and create a watering cycle instead.
“When you water, you fill up the spaces in the soil and squeeze all the air out,” Tom explains. “Some of that water drops out at the bottom and some of it is taken up by the plant before air comes back in replacing the oxygen that went out.”
If you water plants too often you prevent oxygen from coming back into the soil so the roots can breathe again. “You’re basically suffocating it,” says Tom.
This means it’s important to let the soil dry out. “If you’re in doubt, always leave the garden an extra day to dry before soaking it again,” says Tom.
Trial and error
“There are no mistakes in rock gardening, only opportunities to learn,” says Tom.
One of the best things you can do is observe your garden and pay attention to how it grows and evolves. “Watch what happens and if something’s not working think about solutions: ‘Was it too wet?’, ‘Was it too dry?’, ‘Are some plants better in a sunnier spot?’”
How to make sure your rock garden is eco-friendly
Use the right rocks
If you’re using rocks and stones from elsewhere make sure you haven’t destroyed the fabric of the landscape to collect them. “Collecting stones from the bottom of your garden that are already part of the environment is brilliant,” says Tom. “Most of the environmental costs with rock are transport emissions and embedded carbon emissions. So those are the kind of questions you need to think about.”
Re-use salvaged materials
It’s also worth thinking about how you can use reclaimed or salvaged materials to create your rock garden. “There’s junk everywhere which we could be turning into really cool planters,” says Tom. He also suggests making planters yourself by mixing cement, lime mortar, grit and sand and then using something like a polystyrene fish box as a mould.
Choose responsibly sourced plants
Alpine environments are extremely threatened, so it’s important to make sure the plants you buy are from ethical sources. “British nurseries have loads of varieties of alpine plants that are grown exclusively in the UK,” says Tom. “It’s also worth shopping at places that have an RHS Award of Garden Merit.”
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Tom Freeth, rock garden, alpine and aquatics supervisor at Kew Gardens
Tom studied at Kew Gardens before joining the staff at the world-famous royal botanic garden. He is now the rock garden, alpine and aquatics supervisor and looks after Kew’s rock garden, which, built in 1882, is one of the oldest and largest in the world.
Images: Getty, RBG Kew Gardens