Properties on hillsides or with steep slopes come with a number of challenges and opportunities. While proper drainage and erosion control are concerns that need to be tackled, designing a landscape on a sloped site provides a lot of creative potential.
Every site is different so there’s never going to be a one-size-fits-all solution for sloped properties.
“When determining what solution for a property we base them on the site, home design, and client desires,” says Tyler Lindquist, owner of Highridge Landscapes, based in Bozeman, Montana.
Selecting a Solution
Ben Jones, owner The Green Team, based in Knoxville, Tennessee, says they have a lot of success with installing segmental retaining walls. Similarly, Lindquist says they have many opportunities to install retaining walls, using locally sourced natural stone since they’re located in the Rocky Mountains.
“These walls can be created with a naturally occurring square stone providing a more traditional appearance or the use of softer shaped round boulders placed in outcroppings throughout the slope to give a natural appearance that blends in with the surrounding environment,” Lindquist says.
Retaining walls can allow the homeowner to reclaim a portion of their yard with level ground. Multiple retaining walls can be used to create a terraced landscape. Jones says this is a good option when the client wants a usable space but doesn’t have the budget for one large wall or deck.
“Terraces allow our team to be more creative and flexible in the design and construction process,” Lindquist says. “The use of natural stone staircases incorporated into the walls throughout a project allows for easier accessibility and allows for experiences as you pass throughout the site. Softscape opportunities within terraces can be used to soften and accent walls.”
Scott Davies, landscape manager/designer for Bedner’s Farm & Greenhouse, based in McDonald, Pennsylvania, says a terrace might be a good solution if the slope is 1:1 ratio or steeper and there is little need for daily maintenance.
“The overall height of the slope should also be considered,” Davies says. “If there is not enough space or it is not economical to have an engineered wall, then terracing is an alternative to making one vertical wall. The other consideration is what the customer’s view will be. Most customers would rather have the view of looking at some vegetation in the middle of a vertical wall and not just a concrete mass with little to break it up.”
Decks can be an appropriate solution when the site has very steep falloffs or where it would be too costly to safely get equipment into the area to construct a wall or import material to level an area.
“Basically, once you are going above a 25 percent grade you have a decision to make, and many homeowners do not like mowing grades over 10 percent given many circumstances,” Jones says.
Managing the drainage on a sloped property is a challenging task. Lindquist says they first evaluate each site based on the existing and future topography, groundcover, hardscape surfaces, structures, and elements such as retaining walls or water features.
“Our initial focus is to capture water from areas such as gutters, driveways, and patios with surface drains and move it underground to retention ponds or flatter areas of the property that can handle concentrated amounts of water,” Lindquist says.
They direct surface water away from the house, retaining walls and ponds with positive grades and swales. They line swales on severe slopes with coarse angular rock and vegetation to slow the water velocity.
Davies adds that if you’re using a channel to guide water in a certain direction, the volume of water should not exceed the capacity of the channel. If it overflows the system, the water will create new pathways for erosion to cut the surface away.
In one of Bedner’s Farm & Greenhouse’s most creative solutions, they incorporated the use of two drain catch boxes at the top of the slope and piped the runoff to the base of the hill into a French drain system with an overflow for excess water volume.
“This allowed the natural runoff to be collected and taken off the surface rather than continue down the slope allowing it to cut away the slope creating ruts and erosion problems,” Davies says. “Once the surface water problem was addressed the slope was able to be reseeded and get a lawn established that could then be mowed and maintained by the homeowner. The bottom of the slope grew a much richer turf as a result of the increased amount of water that was allowed to slowly filter into the subsoil instead of run freely away from the property.”
Go-To Plant Options
Like how there’s no one good solution for slopes, Davies says the environment needs to be evaluated as a whole to determine what plant material will do the best there. Consider the soil type, sunlight conditions, steepness, exposure, size of the space and more when selecting the plants to install.
“Whatever we chose to install will have an effect on changing the environment on that slope, and that has to be a part of the consideration of what to choose for plant material,” Davies says.
Some of the plant material they do commonly use include Juniperus horizontalis ‘Wiltoni’/Blue Rug Junipers or Rhus aromatic ‘Gro Low’/Gro Low Sumac, Aegopodium podararia/Bishop’s Weed or Leucantheum vulgare/Daisies. For ground cover commonly they tend to use Ajuga repatans/Ajuga or Vinca minor/Myrtle.
In the Rocky Mountain region, Lindquist says perennials and shrubs like Catmint, Little Bluestem Grass, Prairie Dropseed, Sage, Kinnikinnik, Fragrant Sumac, Creeping Juniper, and Mugo Pine do well there.
“Plants are fun on hillsides,” Jones says. “You can utilize creeping junipers that stay very low. You can also add in height factors more easily without the fear of blocking windows.”
Jones says depending on the soil and conditions, red creeping thyme and other creeping perennials are good options. He says most perennials are good for hillsides as they require less maintenance and many times no pruning is needed.