Landscaping on a Slope: An Uphill battle
If you weren't convinced before that slopes were a problem, you should be now. So let's focus on turning those headache areas into landscape assets. After all, a well-designed and -maintained slope can be a wonderful accent or backdrop, as well as functional.
The first step in conquering your problem with slopes is to decide whether to keep growing turf or change the plant material. If you've got problems with a slope for any of the above reasons, it may be time to create a new planting design.
- Replacing turf
Probably the simplest design solution is to leave the slope alone and simply replace the existing turf with groundcovers, ornamental grasses or some other low maintenance material. Hundreds of choices are available, depending on your locale. The big advantage is that they do not need to be mowed, thus eliminating a safety hazard while providing an attractive landscape feature.
Alternative plantings may be a long-term solution, but establishing them can still be problematic. One strategy is to kill the existing turf, but leave it in place. Then you can cut holes in the sod for installing the new plants, and lay mulch of the dead turf.
- Keeping turf
There are three design solutions that involve keeping turfgrass:
In some scenarios, you're dealing with a steep slope that is surrounded on all sides by large areas of flat ground. Regrading the site will spread the slope out over a larger area, reducing the steepness and making it easier to maintain. It's quite possible that simply moving the soil around and re-grassing the area will suffice.
- Terracing or installing retaining walls
When the hill is steep, and adequate room does not exist to spread it out to a more gradual slope, consider installation of a terrace or retaining wall. If you choose this option and the site is complex or very large, consult a landscape architect for advice and a set of drawings.
- Changing management
In addition to physical changes, consider changing your management strategy. Four maintenance techniques will greatly improve the sustainability of a sloped landscape:
- Split the irrigation runs
On flat turf, you may be able to irrigate for 30 to 40 minutes without runoff, providing a one-third to one-half inch of water with one application. Slopes just won't allow for that. Instead of one big soaking, split the application into two or three shorter sprinklings.
So, how do you determine run times? You'll have to experiment. Crank up the system, and run it in the “manual” mode. Watch the slope (and your watch) closely, and when runoff begins, shut the system off. Let the water soak in for a couple of hours, and then run the system again. Repeat this process until the water penetrates throughout the root zone. This process will help you determine the correct duration and number of irrigation cycles.
- Aerate and topdress
Any technique that improves infiltration will reduce runoff. The common maintenance practice of aeration will increase the percolation rate, enhancing downward water movement. After aeration, consider topdressing with compost or processed clay amendments. These products can have a significant effect on infiltration rates.
- Apply plant growth regulators
This strategy is quite simple. PGRs slow the growth of the turf, which results in fewer mowing operations. Identify the times of the year when the turf is growing most vigorously and focus your suppression efforts accordingly. Spring and fall are likely targets for cool-season turfgrasses, while late spring and early summer are appropriate times for warm-season grasses.
- Switch to “No Mow” buffalograss or fine-leaf fescues
Recent breeding efforts have produced several new cultivars of turf-type buffalograss, which may fit in well in the landscape you maintain. Buffalograss naturally grows at a slow rate — so slow that you may not need to mow all season. In addition to slow growth, buffalograss stays short. Unmowed buffalograss seldom reaches more than 8 to 9 inches, which might be quite acceptable on a slope. Certain fine-leaf fescues also can remain unmowed for a similar effect.
- Water the top of the slope only
Earlier in this article, I mentioned the importance of irrigation uniformity. So, does it make sense to water the top of the slope, and not the bottom or the middle? Absolutely. Depending on the degree of slope, water applied to the top will flow downhill, soaking in along the way.
- Split the irrigation runs
As a grounds manager, you have a choice when dealing with slopes. You can continue to curse them or choose to implement changes that will help turn a problem into the asset it was intended to be.
John Fech is a horticultural extension agent with the University of Nebraska Cooperative Extension (Lincoln, Neb.).
PLANTS AT HOME ON THE HILL
Hundreds of plants are potentially suitable as ground covers for slopes, depending on the site and your region. Ice plant, gazania, yarrow, goutweed, Ajuga, Cerastium, lily-of-the-valley, lilyturf (Liriope), lantana, rosemary, rockspray cotoneaster, cranesbill, creeping juniper, Hall's honeysuckle, wintercreeper, English ivy, fountain grass, blue fescue, ribbongrass, lambsear, St. Johnswort, little bluestem, crown vetch and Vinca minor are typical species that you may want to consider.
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