People frequently call in landscapers to take a look at difficult hillside gardens. In Mt. Lebanon, these gardens are often in the front of the house sloping to the sidewalk below from a small flat yard near the doorway. Other times the hillside garden is at the rear of the house, with a steep hill going down or up, abutting a flat patio area.
To say these areas are difficult to develop is an understatement because…they are hard to work on, hard to plant and hard to water. And they are very dry, which means the soil is often compacted so air, water and nutrients are not able to penetrate the crusty top layer and reach the roots of the plants.
However, instead of making do, let’s make lemonade out of these lemons and make it great.
One of my first encounters with a hillside garden was many years ago in Squirrel Hill for a home on a very small lot. The front yard was a steep slope to the sidewalk. A huge maple tree on the right cast deep shade. On the left of the slope, wide cement steps with a wrought iron railing went up the hill to a landing and continued to a beautiful front porch.
The steps created good visual balance with the tree, and at first glance the hillside looked pretty good. Closer inspection revealed that the shrubs on the hill were not healthy. To the left of the stairs was a scraggly patch of myrtle (vinca minor) with some sad looking daffodils sticking up. This vinca and daffodil combo should have worked— daffodils typically do very well in deciduous shade because they bloom before the tree leafs out, giving them enough sun in early spring. But not here.
The homeowners were frustrated. When they tried to water, the water ran down the slope into the street. I began to suspect that severe compaction was the problem. First, a silver maple’s roots are nearly impenetrable; plus, the deep shade cast by the tree’s dense canopy meant little if any rain ever made it to the hillside. If any rain did get through, it ran right off the hillside and poured into the storm sewer.
With the goal of hydrating the hillside, my crew used pitchforks, pushing the tines into the soil, and wiggling them ever so slightly to open the holes, being careful to not lift the soil or disturb the roots. Then we moved over 6 inches and repeated the process until the entire hillside was aerated.
Eight weeks later, the results were noticeable. The plants were healthier and looked better. The color of the vinca was brighter, and it was growing and filling in the way it should. The shrubs also had new color and vitality. Clearly we were on the right track.
The first year, the hillside needed forking four times. The next year, we were confident enough in our success to plant more vinca. The shrubs have grown and look good, even though they are in the shade and compete with the compacted roots of the maple tree. With forking twice a year for many years, plant health remains good, and the hillside is an asset to the front of the house.
With a slope like this, the best way to water is with a soaker hose. And using several thicknesses of newspaper can minimize weeds. After you’ve pulled the weeds, cover the area with six to eight sheets of newspaper, and then spread mulch. The paper will decompose in a couple of years and provide food for the worms and micro-organisms—a better alternative than landscape cloth, which interferes with the natural production of healthy soil.
Here are some other ideas for taming hillsides:
Building or Rebuilding a Wall
A wall is one way to stabilize your hillside garden. Many Mt. Lebanon homes have beautiful stone walls built at ground level to help hold up the slopes. These treasures often were created by true artisans—many of them third or fourth generation craftsmen—and are well worth maintaining. Because our community is aging, many of these stone walls need to be rebuilt. Often, the original stones can be reused, and there are professional stone masons in our area who can rebuild an aging wall or build a new wall. If you have ever had a chance to watch one of these professional masons work, you know it is an experience to see them handle the stone. Above these walls, there is often soft slope, just waiting for something pretty to be planted. I love to use plants and shrubs that will hang over the wall and soften the effect. We will discuss some plants that will thrive a little later.
Planting boulders is another way to tame a hillside. The boulders need to be sized according to the size of the hill. Big hillsides require big boulders. A neighbor of mine longed to create a garden outside her kitchen. A beautiful set of curved stone steps connected the patio outside her kitchen door to the terrace above, which she could not see or access because of a massive thicket of forsythia. Years ago, someone clearly had worked hard to create the landscape, and my neighbor was keen to bring back some of the beauty. When we removed the forsythia, a daunting hillside emerged. The challenge was on. The homeowner was overwhelmed by the size of the hillside and feared she could not take care of a garden on this steep slope. We decided to hire a contractor to bring in large boulders.
Boulders not only provide visual interest with contrasting texture and color, but also provide a foothold. If the boulders are well placed, the gardener can walk from one side of the hill to the other with the pathway of boulders providing access to every area. From a horticulture point of view, the rocks provide planting pockets for the shrubs and perennials, keeping roots cool.
The contractor created a labyrinth with these large rocks, burying each up to two thirds in the soil so they looked as natural as possible while creating access for weeding and maintenance purposes. Twelve years later, shrubs, roses, ground covers and perennials mingle with the rocks, and there is a beautiful view from the kitchen. The homeowner went on to add a bronze statue of a girl sitting on one of the boulders and, at my encouragement, her gorgeous garden was on the library garden tour a couple of years ago—a great example of what can be done with a difficult slope.
Building a retaining wall into the slope is one way to terrace a hillside, but if the hill isn’t too steep, you can terrace a hillside by simply moving the soil and creating the slopes and flat areas. The advantage to terracing is at least two fold: first the plants have a nice flat place to grow, and second, the gardener can access the hillside via the flat areas.
Planting for hillsides
What plants work well on a hillside? Always remember to plan for the mature size of the plant. As a rule, choose plants that once established are dry-soil tolerant and appropriate for your sun or shade conditions. Also, a good 50/50 mix of deciduous and evergreen plants makes for an easy guide when planning winter interest.
For a sunny hillside, try the Flower Carpet family of roses. “Pink Supreme” is the most prolific bloomer and has the nicest arching habit. This shrub rose is about 3’ x 3’ but could get a bit wider. It blooms from early spring until late fall, self-cleans and is disease and pest resistant. What could be easier?
A ground cover like ajuga “Bronze Beauty” underneath the roses adds to the succession of bloom and helps suppress weeds. Finally a low spreading evergreen shrub like juniper “Daubs Frosted” or Juniper “Saybrook Gold” provides good contrast in color with gold tipped branches. It also looks great draping over the boulders and provides great winter interest. Another shrub to consider is the new family of dwarf buddlea called “Lo and Behold.”
For the shady slope, try cephalotaxus harringtonia prostrata or Japanese plum yew. This shrub is deer resistant, does well in the dry shade and has a very pretty draping habit. Dwarf azaleas and rhodies can do well and Pachysandra is a great ground cover for the shade.
Summing it up
Although sloping gardens are a challenge, using some of these techniques will increase your chances of success. Look at your area from the perspectives above and decide which might be the best fit for your real estate. The answer may be as simple as correctly providing water or choosing appropriate plant life.
Claire Schuchman, a professional landscaper, is a Phipps Master Gardener and teaches at CCAC. firstname.lastname@example.org