Smart Solutions for Steep, Sunny Slopes

A steep, sunny slope in your landscape can be a real challenge, especially if you’re trying to manage that area as a lawn. The slope itself makes mowing difficult -- if not outright dangerous -- and it is difficult to keep the turf green, as most water simply flows downhill, leaving the hillsides brown and barren. A proper solution should really turn this landscaping liability into an attractive asset.

There are a number of suitable solutions, but most are fairly expensive, such as designing and installing retaining walls, along with extensive replanting. Moreover, if the angle of your slope exceeds 20 degrees, you may need to engage a soils engineer or landscape architect. There might even be heavy equipment in your future. Ka-ching!

A simpler fix, ideal for the do-it-yourselfer, would simply call for replacing turf grass with a low maintenance ground cover. Keep in mind that many of the most popular ground covers are actually invasive weeds, and can often create management headaches in their own right. These include Five-leaf Akebia, Japanese Barberry, Crown Vetch, Wintercreeper (Euonymus fortunei), and English Ivy, which can often bake in full sun. Moreover, the “wild” nature of such plants makes mulching difficult, and can lead to even more weeds taking hold. So much for low maintenance!

For my money – or yours – one of the best solutions is an evergreen groundcover: something with an obedient and predictable growth habit, and an attractive year-round appearance. Think juniper.

There are literally scores of procumbent juniper species, and similar conifers, which will happily bask in the hottest sun, stretching across your hillside over the course of several years, all providing excellent erosion control and weed suppression, especially when combined with diligent annual mulching, and saving you the need to combine mowing with mountaineering. And these hardy plants are almost always drought-tolerant, helping to conserve water, while requiring no fertilizing.

Among the most common and popular junipers used as groundcovers are the creeping junipers (Juniperus horizontalis), slow to medium-growing shrubs, which form dense, aromatic mats between 12 and 18 inches in height, extending trailing branches from four to eight feet across, depending on the cultivar. Most feature either soft or prickly scale-like bluish-green foliage, which often “bronzes” once hit by cold winter temperatures. But don’t worry, they will “green up” again in the spring as air and soil temperatures warm up.

Blue Rug or ‘Wiltoni’ is probably the most popular juniper sold. It hugs the ground at four to six inches, and provides coverage up to eight feet in diameter. Blue Rug is drought-tolerant and thrives in conditions ranging from coastal Maine to the mountains of Georgia.

Other popular cultivars offer a Mardi Gras parade of colors and shades, from gold to green to purple, in a range of heights. Favorites include ‘Bar Harbor,’ which is similar to Blue Rug, although more colorful in winter, the bright green ‘Emerald Spreader,’ four-to-six inch tall ‘Prince of Wales,’ gold-variegated ‘Mother Lode,’ and ‘Pancake,’ lowest of the low at two-to-three inches.

‘Blue Star’(J. squamata) is a taller, different species, featuring cool blue foliage, and a pyramidal growth habit. This selection will generally stay below two feet in height, but can reach three feet, with only a two to four foot spread. It would be especially useful under a retaining wall for terraces, or against a rock outcropping.

Not all junipers are groundcovers: some are actually full-grown trees, like our native Eastern Red Cedar, which reaches an impressive 30 feet. Others tend to be shrubs, useful as hedges, such as the Chinese Junipers (J. chinensis), which reach about six feet in height, although some can become small trees up to 20 feet. One notable exception is Sargent Juniper, a cultivar that hovers at about 18 to 24 inches with an eight to ten foot spread. Many landscapers turned off by a juniper’s tendency to turn bronze in winter prefer Sargent, as it keeps its grayish-blue color year-round.

Dwarf Japanese Garden Juniper (J. procumbens ‘Nana’), provides bluish-green foliage which turns a stunning purple-bronze in late fall and winter. Horticulturist Mitch Baker (my go-to guy) at American Plant in Bethesda, Maryland is enthusiastic about ‘Nana’s’ spray-like mounding habit, which provides an exciting departure from the flat mat-like appearance of many other species, and allowing for a level of dimension to your hillside.

Mitch also noted options beyond junipers, such as the confusingly-named Siberian Juniper (Microbiata decussata), which is also called either Russian Arborvitae or Siberian Carpet Cypress, due to the shape of its foliage. Siberian Juniper is fairly new on the market, but is quite versatile thanks to its tolerance for Siberian winters and partial (not full) shade, as well as average soil and dry conditions. This specimen’s feathery foliage stays within eight to 12 inches in height, with an above-average ten foot spread.

And “spread” is the name of the game with junipers and other ground covers. Obviously, the wider the area covered by the plant, the fewer plants you will need. Most junipers can be planted approximately six feet apart, although you should check – and do the math – before purchasing and planting. Larger container stock, about three gallons, will provide a vigorous root system, ideal for early season planting, and will get your hillside off to a fine start.

Costs can range from 15 to 35 dollars, depending on the cultivar, size, and source. Smaller containers will be less expensive, but might take years to fill in. Don’t make the mistake of buying a lot of smaller containers and planting them too close together to create a finished look. Overcrowding can lead to disease problems and might require substantial transplanting in just a few years. Remember, you want a low-maintenance landscape: plan and plant properly, according to your budget, and let time and patience do the rest.

Decide in advance if you want to address the entire hillside at once, or just tackle a portion at a time. For best results, smother the grass or weeds on the site with landscape fabric or cardboard and a three to six inch layer of shredded wood mulch. Shredded mulch will lock together in place, where nuggets or chips might be washed off. Be sure to stagger your planting holes so that plants can diffuse flow down the slope and prevent erosive gullies. Check your soil to see if it needs amending with compost – although most junipers are tolerant of relatively poor soils as long as they receive good drainage.

Copyright 2009, Joseph M. Keyser