Gardening on Hillsides

A few years ago I visited a friend's farm in Ohio. Envy immediately crept in. Her whole place was flat. For those of us living in the Rocky Mountain region, we usually have hillsides that need to be dealt with.

Cotula sp. ‘Tiffindell Gold’
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  • Topic: High Altitude Gardening
  • Author: Cindy Bellinger
  • Keywords: garden design, site preparation
  • Date: March 2006

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A few years ago I visited a friend’s farm in Ohio. Envy immediately crept in. Her whole place was flat. For those of us living in the Rocky Mountain region, we usually have hillsides that need to be dealt with.

Living on a mountainside for nine years has not only pushed all my muscles but my imagination as well, trying to create planting areas. But there are a few tricks to slope gardening that really help with the inherent problems.

Analyze the Site

Water, whether it comes in streams, rivers or rivulets, always takes the path of least resistance. If you have a chance and the willpower, wait a year before reworking a hill. This allows you to understand the character of a slope and see how water naturally angles down its face. The information you’ll gather is two-fold.

  • You’ll see the direction the water takes and be able to decide which areas need stronger reinforcements. And yes, you might consider getting out in the rain and marking the path with stakes. It’s a little miserable at the time, but well worth it later. It’s amazing how quickly you’ll forget the path of small waterways when the rain stops.
  • By noting the gathering places of water can supply you with ideas for garden designs. In the low lying places, consider using these natural basins for plants that like their roots a bit damp.

Making Barriers

If you want to terrace an area, there are many materials to use to “level out” a slope. The most common materials include—

  • Brick
  • Stone
  • Landscaping cinder block
  • Pressure treated wooden planks

If you can find untreated railroad ties (not easy!) that’s a great way to go. If not, try 2×6 or 8″ wide planks. These also can be cut them to fit angles and curvatures. Stabilize them with rebar on the downhill side. If you go up two layers with boards, before backfilling with dirt, line uphill side with geotextile (weed barrier cloth) to lessen seeping of soil and water under the bottom board and through the crack between boards. The drawback to using wood, though, is after awhile they’ll begin to rot and will eventually need to be replaced.

Using Plants for Stabilizing

Plants should be used to stop erosion by themselves and in combination with constructed barriers. Plants are especially useful to help cover-up and soften the look of constructed materials. Choose perennials with deep roots and groundcovers with spreading stems to hold the soil against erosion.

Perennials and Groundcovers

  • Penstemons are great for slopes because they reseed and spread. Plant toward the top so the seeds can fall downwards. (P. palmeri, P. psuedospectabilis, P. strictus)
  • Blue Flax, Sundrops, Prairie coneflower, Chocolate flower and Gaillardia also reseed easily.
  • Oenothera caespitosa does well on a slope and reseeds itself.
  • Snow-in-summer, Big Leaf Periwinkle and Cotula sp. ‘Tiffindell Gold’ are excellent groundcovers for carpeting slopes with protective stems and roots.

Shrubs

  • Rhus trilobata ‘Autumn Amber’ (Three Leaf Sumac #82561) is a low-growing native shrub with flat growing branches that will spread quickly over an area.
  • Prunus besseyi ‘Select Spreader’ (Spreading Sand Cherry) is another native that works well as a large scale groundcover for sunny slopes.
  • Fallugia paradoxa (Apache Plume #51450) is often found on slopes along highways, needs little moisture and is fairly deep rooted.

Grasses

  • Agropyron sp. ‘Mora Blue’ Blue Bladed Wheatgrass is an aggressive stoloniferous, western grass recommended to hold the soil in dry ditches, along the sides of road cuts and on slopes where it can be interplanted with colorful native wildflowers.
  • ‘Hachita’ Blue Gramagrass #27056 roots go very deep after a year or so and makes a nice fill between flowers and shrubs.
  • ‘The Western Trails’ Native Grass Seed Mix #99580 contains a superb mix of soil holding native grass species that is useful on sloping areas.

Another trick that David Salman suggests for hillside planting is to cut 4″ deep rims off the tops of used 1, 2 and 5 gallon plastic containers. Push the rims into the soil around the plants and use them as watering wells for the first year. This helps the water soak more deeply into the soil where the roots will follow, instead of spilling down the hill where the plants can’t use it.