Whether you have a steep, sloping garden or just a small bank, there are some key facts you need to know about hillside gardening.
However, once you understand the principles, you are not limited to any particular ‘plants suitable for sloping gardens’. You can plant the plants you like.
So I spoke to Richard and Lesley who have a large sloping garden on a steep mountain. What I have been told applies to smaller gardens and even a relatively small change in level. The only difference is that if your garden is either smaller or less steep, then gardening will probably be a little easier for you!
But there is no better source of reliable information than people who actually garden on a slope (rather than a set made by someone working in an office!).
Embrace your sloping garden
Lesley says the first step is to ’embrace your inner mountain goat.’ By this she means that gardening on a slope is different from gardening on a flat, and it is important to accept that.
This applies to making changes, such as landscaping, as well as regular maintenance, such as planting and watering.
Although she was a very experienced gardener, Leslie had never gardened on a hillside before moving here seven years ago. So she had to accept that she had to learn different strategies and techniques.
She says you have two options. ‘One is to accept the slope and work with whatever slope you have.’
Another is to create flat surfaces by creating terraces. This will mean hiring a landscaper or arranging the landscape yourself.
Lesley and Richard combined both approaches, which is also another option.
Sloping or terraced? Richard and Lesley planted shrubs, such as roses, on sloping land, but created terraced raised beds for growing vegetables.
See the slanted border from multiple angles
If your borders are straight, you can see them from the front. And if you have tracks all around, you can also see them from the back or from either side.
But you see the sloping border both above and below. Those are two potential additional perspectives.
‘So you have to think about those new angles when you plant.’ Leslie also finds these two additional perspectives to be both the best and the worst of the sloping garden. ‘Those are wonderful things. And they are also challenges. And that can mean you can get a longer view in a sloping garden than in a flat garden.’
Two views of Richard and Leslie’s main sloping herbaceous border. The top photo shows a view looking up, while the second shows a view looking down from one side.
Therefore, do not follow the usual rules about the height of plants
“The traditional ‘tallest at the back, smallest at the front’ planting method doesn’t work in a sloped border,” advises Leslie.
‘Sometimes you have to be brave and put a tall plant in the front or to the side,’ she says.
The extra height means you can plant shorter plants further up the slope, in the middle of the border.
If you plant smaller plants in the front, with taller ones in the back, the border can look like the planting is sliding down a hill.
Lesley does plant some smaller plants out front, but they sit side by side with the larger ones.
In which direction does this border slope? In fact, there is not much difference in height between the agastache, monarda and veronicastrum, but the lowest plants – the agastache – are actually at the top of the slope in the foreground. This border is indeed sloping down away from the place where the photo was taken!
The steps are lined with low growth Alchemilla mollis, but the Cotinus ‘Royal Purple’ behind is taller than the yellow rudbeckia further up the sloping border.
Start with one edge
If you’re new to hillside gardening, Lesley suggests getting to know your garden gradually.
Leslie and Richard’s garden dates back to the Victorian era when the house was built, but in recent decades has been very neglected. There were lots of old rhododendrons, 19th century drywall and lots of self-seeded weeds. ‘We decided to start with the garden closest to the house and work outside,’ says Lesley.
The closest border to the house is also the main grass border. Lesley says she learned so much about slope gardening by trying to get one border right. ‘I was prepared to take things out or move things if they didn’t work.’
Many parts of the garden were almost wild when Richard and Lesley moved in. Even after 7 years, there are still a few areas that they still haven’t decided what to do with.
Is the slope facing or away from the sun?
It is important to determine whether you have a sunny or shady slope.
‘Phototropism – plants leaning towards the light – is worse in sloping gardens,’ says Lesley.
Check where the sun and shade fall in your sloping garden. The shady end of this sloping border is closest to the house. It is planted with euphorbia, Japanese anemone and other shade lovers. In fact, shady sloping borders are easier to plant than sunny ones, according to Lesley, because shade-loving plants are less likely to lean towards the sun.
Stakes are very important in the lawn garden
Lesley found that it is vital to place and support plants growing in a sloping bed.
Its main herbaceous border faces south, but they are in Australia, so it is equivalent to north in the UK and USA. “However, it’s not completely south-facing – it’s angled, so the plants can grow towards the sun, as if leaning at an angle,” she says.
In our post on planting in a shade garden, horticulturist Stephen Ryan says that plants tend to lean too much if they are sun-loving plants that are planted in too much shade. However, this border is quite loose and open. Lesley has successfully grown lilies, monards and cannas, so she corrects only a small amount of thinness.
He uses a variety of supports from single types of ‘shepherd’s crooks’ and hoops to homemade natural supports made of twigs.
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She also occasionally even uses several lengths of fence to hold very heavy items. ‘As soon as the first shoots sprout in the spring, I have to remember how tall some perennials are. Then the border looks like an industrial landscape for a few weeks, but soon the plants are growing over the supports.’
A bed for ‘Shepherd’s crook’ plants in Richard and Lesley’s garden.
Always mulch a sloped garden
In researching sloped gardens, I’ve come across a few sites that suggest you should plant ‘mat forming plants’. The idea is that the roots help prevent water and soil from washing down the slope.
Lesley didn’t deliberately plant ‘mat making plants’ – she planted plants she loves.
‘The most important thing is to mulch the sloping edge instead,’ says Lesley. ‘A good mulch of something coarse like composted bark helps stop water running down the hill. The water is more likely to soak into the soil and reach the roots of the plants.’
‘And when you’re planting, create some informal mini-terraces,’ she suggests. Here is a good post on how to plant on a slope.
In it, Stephen Ryan suggests using coarse mulch, such as Richard and Lesley’s composted bark or straw. It will let the rain through but stay put. If you want to use compost or garden manure, he adds a layer of coarse mulch on top to hold it all in place.
Lesley digs a hole that is deeper at the back than at the front, so the water doesn’t run straight down, but stays in the planting hole. She often also jams the plant with a rock or brick until it is established.
Newly planted plant surrounded by Lesley and Richard’s bark mulch. If you try to water a slope that is not mulched and has dry, exposed soil, the water will just run off. But water can run off through the mulch and soak into the soil.
Good plants for a sloping garden
People often advise you to grow plants with deep tap roots or plants that form mats on slopes, but Lesley has successfully grown many bulbs, along with monard, agastache, roses, euphorbia and agastache. ‘We have critters that eat roses so I plant roses in the middle of the border in the hope that possums and deer won’t get to them,’ she says.
It is more important to choose plants according to the amount of shade or sun you have or according to your soil type. Provided you mulch well, then you are not limited in the range of plants you grow.
You are more likely to have drought problems on a slope. You can find good hardy plant suggestions in 10 Beautiful Hardy Perennials for Wet or Dry Summers.
You can also theme the slope. For example, a rock garden makes good use of a sunny slope. And a stump works well for a shady slope.
If you are thinking of planting a sunny slope, rockery plants will come in handy. And if it’s a shady slope, then think about forest plants or even make a tree stump. Rock garden and rock garden at Doddington Place Gardens.
Slope landscaping – access is often difficult
Richard points out that access can be a problem in many gardens on sloping sites, as it can be difficult to use large mechanical diggers if the ground is too sloping.
This means that landscaping on the lawn can be more expensive than it would otherwise be, as most of it has to be done by hand.
Although there was already a certain amount of Victorian terracing in the garden, some of the slopes had also lost definition.
So Richard taught himself how to make dry stone walls, using YouTube videos.
He also built a giant cage for growing fruit and vegetables, terracing most of the interior. There are so many ‘things’ – deer, wallabies, possums, parrots, rabbits and more – after produce that it’s simply not possible to grow fruit and vegetables successfully without protection.
The mesh enclosure has three terraced levels, with paving, raised beds and steps. Lesley says the contrast between the straight lines and relative formality of this area makes a good contrast to the more informal sloping borders.
See more about the sloping garden in the video
There are some nice views of the borders as well as more details on the mesh enclosure in this video.
Attach to remember the secrets of the garden on a sloping place
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