How to Plant on a Slope: Tips and Techniques for a Stunning Hillside Garden

Planting on a slope can be challenging, but with the right techniques, you can transform this difficulty into a stunning garden feature. Even in my small sloping garden area, I’ve noticed plants struggling because I wasn’t sure about the best planting methods.

The main problem is that water tends to run off quickly, taking valuable soil with it, instead of soaking in properly.

Despite these challenges, sloped gardens offer undeniable benefits. They create a dynamic display of layered planting, and each plant enjoys better exposure to sunlight. However, managing a sloped garden comes with its own set of problems.

Erosion is a major concern, especially on steeper slopes where the lack of strong plant roots means there’s little to hold the soil in place.

Planting on steep inclines requires special care. If not done correctly, you might end up with partially buried tree bases or perennial roots. Slopes can also make everyday gardening tasks like weeding more difficult. Watering becomes tricky too, as water often runs off before it can soak into the ground, leading to drier soil.

By using the right strategies, though, you can create a beautiful and productive sloped garden. This not only enhances your outdoor space but also helps manage erosion and water runoff effectively.

Preparing to Garden on a Slope

Gardening on a slope is like being a mountain goat in the plant world—it requires adaptability and a sense of adventure. Unlike flat gardens, sloped terrains present unique challenges for landscaping, planting, and maintenance.

As someone who ventured into slope gardening seven years ago, I’ve learned that it’s crucial to develop new strategies and techniques.

When tackling a sloped garden, you have two main options: work with the natural gradient or modify the terrain by creating terraces. This decision might involve hiring professional landscapers or taking on some ambitious DIY projects. In my experience, a combination of both approaches can be effective.

• Understanding Slope Dynamics

The steepness of a slope directly affects its potential for erosion. Factors like soil type, plant cover, and water runoff from higher ground all play important roles. Slopes are typically measured as a rise-over-run ratio or a percentage.

Generally, gentle slopes of less than 5% don’t pose significant challenges. However, when you’re dealing with slopes between 8-16%, you’ll need to consider specific planting strategies, as these angles can make gardening and watering more difficult.

• Soil and Drainage Considerations

Steep slopes tend to be drier, which may require the use of drought-resistant plants. It’s important to examine the soil conditions across your slope—some areas might be wetter, especially at the base, while others could be drier or show signs of erosion.

Understanding whether your soil is rocky, sandy, or rich in organic matter is crucial for selecting the right plants.

• Assessing Growth Conditions and Existing Vegetation

Before planting, take note of your slope’s exposure to sunlight and wind. Choosing plants that thrive in these specific conditions can reduce maintenance efforts. Keep in mind that the slope’s orientation can affect plant growth, as plants on inclines tend to lean towards light sources more noticeably than those on flat ground.

Your slope may already have some vegetation, such as grass, which can be challenging to mow on an incline and might not effectively control erosion. Consider whether any existing plants need to be removed, and remember that certain weed-killing products can allow you to replant quickly if needed.

• Unique Viewing Angles and Aesthetic Opportunities

A sloped garden offers distinctive viewing perspectives that flat gardens can’t match. You’ll be able to see your garden from above, below, and straight on, providing multiple viewpoints. This unique feature can be both a benefit, offering expansive views, and a challenge, requiring thoughtful planting to make the most of these varied perspectives.

Managing Erosion on Slopes

Erosion on sloped areas can be a significant challenge, but there are effective strategies to address it. The main issue with slopes is that water tends to flow downhill rapidly, washing away soil and vital nutrients. Here are some practical solutions to combat erosion:

• Swales and Water Management

Consider digging shallow trenches, or swales, across the slope. These should be about 3-4 inches deep and, once planted, will be barely noticeable. Swales trap water, allowing it to slowly soak into the soil. Over time, they’ll naturally fill in with plant growth and fallen leaves. By then, your plants should have developed strong root systems.

If you’re using an irrigation system, align it with these swales for efficient watering. Another option is to create a rock garden filled with drought-resistant plants, which is both practical and visually appealing.

• Planting for Stability

Adding plants to a slope helps stabilize the soil and retain moisture. For a more structured approach, terracing is an excellent method. Use materials like retaining walls, boulders, or wooden timbers to create level planting areas, which help slow down water runoff.

• Protecting the Soil

To further shield your soil:

1. Apply a thick layer of mulch around plants. Choose coarse-textured, natural mulches with angular edges, such as shredded bark or leaf mold. These are less likely to slide downhill compared to smoother mulches like river rock.
2. Ensure good plant coverage. A mix of plants at different heights helps break the fall of raindrops and minimizes erosion. Groundcovers are particularly effective at protecting the soil surface. Combining these with layers of trees, shrubs, and perennials can significantly reinforce the soil.

• Controlling Water Flow

Slow down water on slopes by using staggered plantings. This prevents water from pooling and carving paths down the slope. If you need to plant in rows, orient them perpendicular to the slope or along its contour lines to disrupt water flow and reduce erosion.

Manage water flow from the top of the slope by diverting runoff from areas like driveways and downspouts. You can do this by creating diversionary trenches or installing drainage solutions at the slope’s crest. By managing excess water, you significantly decrease the risk of erosion, helping to keep your slope stable and fertile.

Good plants for a sloping garden

When planning a garden on a slope, choosing the right plants is key. Slopes often face tougher conditions than flat areas, including strong winds, intense sunlight, and occasional dry spells.

It’s best to choose hardy, low-maintenance plants, especially since caring for them can be tricky due to limited access. Native plants are often the toughest and most suited to these challenging environments.

For instance, covering a hillside with native prairie plants not only reduces upkeep compared to regular mowing but also adds a beautiful variety of plant life to your space. Any plants you pick for a slope should be able to thrive in these conditions.

When selecting plants, think about what suits your slope’s specific situation – whether it gets lots of sun or shade, and if the soil is usually wet or dry. Many slopes drain well, making drought-resistant plants a smart choice.

Go for plants that don’t need frequent care. Regular tasks like pruning, watering, and removing dead flowers can be hard work on a steep hill, so it’s best to choose varieties that need little attention.

Use a mix of different plants to make your hillside look good and help prevent soil erosion. Combining various plant sizes and types not only looks interesting but also helps hold the soil in place and manage rainwater runoff. Plants with different root systems are especially good at stabilizing the soil and controlling erosion.

While farming experts often suggest using deep-rooted plants to stop erosion, garden slopes are usually smaller and might have different needs. Still, deep-rooted plants like cardoons, comfrey, coneflowers, agastache, red orach, and veronicastrum work well on slopes. They help hold the soil and keep moisture once they’re established.

If you want more plant options, try searching online for “shrubs with deep roots.” Just make sure to double-check how deep the roots actually grow, as some plants might not have roots as deep as advertised.

When it comes to arranging your plants, slopes offer a unique view. From below, it’s easier to appreciate plants of similar heights. But from above, you might want to put shorter plants in front to keep the view clear. Weeping trees and sprawling plants can add drama and movement to your sloped garden.

Don’t be afraid to try unusual choices – bulbs, bee balm, and roses can all work well. Just make sure to match the plants to how much sun your slope gets and what type of soil you have.

Remember, adding mulch is a great way to help combat the naturally dry conditions on slopes. Whether you want to create a rock garden or a woodland-inspired space with old tree stumps, choose a style that makes the most of your slope’s natural features.

How To Plant On A Slope

When designing a hillside garden, you have two main planting options: seeds or transplants. Your choice depends on the area’s size, slope steepness, and budget.

Transplants offer immediate impact and can come from dividing existing plants in your garden or purchasing bare-root or potted specimens from a nursery. While potentially more expensive, especially for larger areas, transplants establish roots faster and cover ground more quickly.

This method also minimizes soil disturbance, as you can plant directly into existing vegetation, helping to reduce erosion.

When planting potted or bare-root species on a slope, ensure proper depth. Avoid burying tree trunks or perennial crowns, as soil can easily wash over these parts. Position the root ball level with the hill’s upper side, then add soil on the lower side for stability.

Use stones, bricks, or even pot halves to prevent soil shift. These supports can be permanent or temporary, with biodegradable materials like cardboard naturally decomposing as the plant grows.

For gentler slopes, consider planting smaller items like bare-root plants or plugs at a slight angle to ensure adequate root coverage. They’ll straighten as they grow. Larger, woody plants should remain upright to avoid a long correction period.

To effectively combat soil erosion and runoff:

• Stagger your plants instead of aligning them in rows to break up water flow.
• At the slope’s peak, direct water towards a drain or rocky areas to minimize runoff in newly planted zones.
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• Choose smaller plants to reduce digging and disturbance, saving on costs and long-term maintenance.

Seeding is a cost-effective option for large areas. Prepare the seed bed by clearing existing vegetation, then sow your seeds. Protect them with straw or chopped cornstalks to retain moisture and prevent wash-away during watering or rain. A temporary cover crop like annual rye can quickly stabilize the area until permanent plants establish.

Plant just below small ditches to help with water management. Create a basic retaining wall at the planting hole’s lower edge using a large stone or a couple of bricks, forming a small water reservoir.

Plant as usual, enriching the hole with soil and compost, and water both the plant and the ditch above. Finally, add a layer of mulch to conserve moisture and further secure the soil.

Always mulch a sloping garden

Many experts recommend planting mat-forming plants because their roots can help secure the soil and manage water flow. However, if these aren’t your plants of choice, focusing on effective mulching can be just as beneficial.

Using a rough mulch, like composted bark or straw, is ideal for sloping areas. This type of mulch allows rainwater to seep through yet is substantial enough to remain in place, reducing runoff.

When planting, consider a technique I like to call ‘informal mini-terracing.’ By digging a planting hole that’s deeper at the rear than the front, you can create a natural basin for water to collect rather than flow away. It’s also handy to secure the plant with a rock or brick until it’s well-rooted and stable.

If you’re looking to enrich the soil, layer your organic compost or manure first, then top it with your coarser mulch. This keeps the nutrient-rich material from washing away and helps maintain moisture.

For even better stabilization, consider a thick layer of chunky wood mulch or even jute matting. Aim for a mulch depth of about 60mm to 75mm, ensuring it’s bulky with minimal fine particles. This strategy not only prevents weeds but also helps to stabilize your slope, conserve moisture, and protect your lovely plants.

Watering

Mastering the art of watering is crucial for a thriving slope garden. When gardening on a hill, ensuring your seeds and young plants receive adequate water can be challenging. Water tends to run downhill before it can soak into the soil, making it difficult to keep roots sufficiently moist.

Drip irrigation systems, including soaker hoses, are ideal for keeping your slope garden hydrated without overwatering. These systems deliver a steady, controlled amount of water directly to the soil, allowing roots to absorb moisture more effectively.

If you don’t have access to a drip system, try this simple method: water each plant until you see runoff, then move on to the next one. Return to each plant and repeat the process until the soil around the roots is adequately moist. You can also create small soil berms on the downhill side of each plant to help retain water around the roots for longer.

For areas where you’ve sown seeds, use a gentle watering method such as a misting sprinkler. This prevents seeds from washing away. Stop watering as soon as you notice runoff, and resume after the water has soaked into the ground. Use multiple short watering sessions to ensure deep soil penetration.

Learn How to Use Ollas for Water-Efficient Gardening

Garden Maintenance Tips for Sloped Areas

Maintaining a sloped garden isn’t too different from caring for other parts of your yard, but it does have its unique challenges. Choosing plants that thrive in your specific conditions can drastically reduce upkeep, particularly after the garden is established.

It’s essential to manage weeds early on as they can quickly overrun the area, stealing vital nutrients and water from your plants.

To prevent soil erosion—an all-too-common issue on slopes—keep an eye on how water travels down your garden. If you notice any channels forming, it might be time to make some adjustments to your landscaping.

One smart strategy is to use mat-forming plants, which spread their foliage wide to create a dense ground cover, naturally suppressing weed growth by blocking out sunlight. Not only do these plants hold the soil in place, but they also make it tough for weeds to find the light of day.

In terms of plant choice, consider those with sprawling roots like ferns and ivy, which are excellent for stabilizing slopes. Some varieties of euphorbias and persicarias are also effective, though they prefer moist environments.

Staking and supporting plants on slopes are crucial to prevent them from leaning too much, especially in a garden like mine which, while south-facing, is more akin to a north-facing garden in the UK or the US. The slight angle helps plants tilt towards the sun without overextending.

To support my plants, I use everything from simple shepherd’s crook stakes to hoops and even makeshift supports crafted from twigs. Occasionally, I even use sections of fencing to hold back the heftier plants. Remember to start supporting plants early in the season, as some perennials shoot up quite tall.

Access is another consideration in sloped gardens. The steep grades can limit the use of heavy machinery, making certain landscaping tasks pricier and more labor-intensive as they must be done manually.

Despite these challenges, I’ve learned to adapt. I even taught myself to build dry stone walls through online tutorials and constructed a massive protective cage for growing fruits and veggies.

With deer, wallabies, and other critters around, it was the only way to ensure a successful harvest. This structured, terraced setup contrasts nicely with the more natural, free-form look of the rest of the garden, providing both functionality and aesthetic appeal.

Slope Garden Ideas for Planting on Hillsides

Think about transforming a hilly area into a series of terraced flower beds or a stunning rock garden. Here’s how you can turn that uneven terrain into a gardening wonderland.

• Floral Walls: Consider building a retaining wall on your slope. This isn’t just practical—it’s also a chance to create a living piece of art. Opt for materials with gaps where you can tuck in plants like sedums, which will cascade beautifully down the sides.
• Water Features: Why not add a dynamic waterfall to your sloped garden? A steeper grade is perfect for creating a dramatic waterfall, turning a simple gardening project into a breathtaking focal point. Just make sure you have a power source for the water pump.
• Container Displays: Utilize the slope to show off your favorite potted plants. Setting them up along staircases or edges of your garden can make them stand out, offering a lovely view as you enter the area.
• Staircase Gardens: Soften a steep slope with a winding staircase flanked by drought-resistant plants and succulents, making each step a visual treat and helping to control soil erosion.
• Tiered Terraces: If a single retaining wall feels too imposing, break up the space with several shorter walls, creating terraced levels. Why not pave one level to set up a cozy patio with seating to enjoy your handiwork?
• Native Plantings: Turn a slope into a low-maintenance garden oasis with native plants and rocks, blending seamlessly into the natural landscape while conserving water.
• Groundcover Glory: Plant groundcover that will forge a dense root system, anchoring the soil and minimizing erosion effectively. Plus, they keep weeds at bay.
• Deck Out Your Slope: A multi-level deck can transform a steep slope into valuable, usable space, striking a balance between natural greenery and structured, stylish decking.
• Boulder Beauty: Integrate boulders into your slope design for stability and aesthetics. Grouping rocks and surrounding them with plants can create a pleasing, natural look.
• Functional Steps: Incorporate broad, meandering steps to make your slope both accessible and inviting. This makes the climb much more manageable and visually appealing.
• Stream Dreams: On a gentler slope, a babbling brook can add a serene element to your garden, helping with erosion control and moisture management.
• Connecting Zones: Use stone walls and steps to link different areas of your garden, such as a pool house or a spa, enhancing the flow and utility of your outdoor space.
• Vertical Garden Variety: Stack your slopes with terraces full of colorful perennials that bloom from spring to fall, creating a lively display throughout the seasons.
• Elevated Escapes: Fit an outdoor living area into your slope, complete with privacy and scenic views, ideal for relaxation and entertaining.
• Textural Designs: Lay down a tapestry of low-maintenance groundcover for a carefree gardening solution, perfect for busy gardeners.
• Secluded Nooks: Transform utilitarian spaces into stunning visual features with colorful plants and strategic rock placements, crafting a private haven.
• Garden Galleries: Divide a long slope into segments, each serving as a distinct garden room, connected by stone pathways for easy navigation.
• Artistic Angles: Use the unique angle of your slope to create visual art with structured plantings like boxwood hedges and contrasting grasses, enhancing the overall aesthetic of your garden.

Frequently Asked Questions  

• Should I mix different plants when creating a garden on a slope?

Absolutely! It’s not wise to stick with just one type of plant when landscaping a slope. A single species can make any imperfections like dead plants or weeds stand out. Instead, go for a vibrant mix of trees, shrubs, perennials, and ground covers. This not only looks great but also helps absorb rainwater, reducing erosion.

• What’s the best planting strategy for a low-growing garden on a slope?

For those preferring a shorter garden, consider planting various groundcovers that bloom at different times throughout the year. Letting them compete naturally allows the strongest and most suitable plants for your conditions to thrive.

• Which plants are ideal for planting on slopes?

Ground covers that root along their stems are perfect as they form a solid mat, reducing soil erosion. Clumping plants and deep-rooted varieties like prairie plants also hold up well on slopes. Don’t forget about ornamental grasses and sprawling shrubs, including rose shrubs. Native plants are generally a fantastic choice due to their adaptability.

• Can I plant wildflowers on a slope?

Yes, wildflowers add beautiful, seasonal interest and are relatively easy to maintain on slopes. To encourage them to reseed, cut them back after they’ve bloomed and the seeds have matured, especially in colder regions. Initially, regular weeding will help them establish. Just make sure the slope is accessible for maintenance and sowing.

• Are no-mow grasses a good option for slopes?

Definitely check with your local Cooperative Extension System to see if Buffalo Grass or Fine-Leaf Fescue, which require little to no mowing, are suitable for your area.

• Can I grow regular turf on a less steep slope?

Yes, you can grow regular turf on slopes that are not too steep (less than 25% grade and wider than 10 feet). However, watering efficiently is crucial, as water can easily run off, leading to waste, especially in dry regions.

• Are there plants I should avoid on slopes?

Be cautious with plants known for being aggressive growers as they can become invasive. Always verify with your local garden center or extension office before planting. Beware of plants like Crown Vetch, Japanese Barberry, Scotch Broom, and Virginia Creeper.

Also, plants like English Ivy and Vinca, although effective, need containment to prevent them from invading adjacent areas. Avoid shallow-rooted trees as they pose a risk of falling.

• What additional considerations are there for planting on steep slopes?

Planting on steep slopes can be tricky and may lead to erosion problems. It’s wise to consult with a landscape contractor to ensure that your gardening plans won’t negatively impact your home’s safety.

• What are some great plants for a slope?

Grasses and Sedges

Herbaceous Groundcovers

Herbaceous Perennials

Woody Shrubs

*List from ISU Extension