Slippery Slopes

Everyone knows that hanging a pool, pond, or spa off a slope can make quite a dramatic statement, which is probably why so many great watershapers love working on hillsides.

But the project doesn’t begin and end with the vessel: In fact, placing a watershape on an incline also presents a range of landscape-related issues that must be addressed, whether it’s a matter of aesthetics, code or safety requirements or simple practicality.

Aesthetics are always a factor in a good overall plan, while slope stability is the motivating factor behind safety and code requirements – particularly when the watershape is at the top of the incline. Practicality is especially important when the watershape is in the middle or at the bottom of the incline, where you need to consider ways to keep soil and debris channeled away from your creation.

Some of these issues are addressed through basic drainage and retaining structures, but if you use plants to help stabilize a slope, there is always a great payoff when it comes to beautifying a watershape’s surroundings.

SOLID SOLUTIONS

As is the case anywhere in a yard, the planting of shrubs, trees, and perennials adds dimension, color and texture that serve to enhance any watershape’s appearance. When you’re working with a slope, however, the most important plant is a good, stabilizing ground cover.

But even ground covers sometimes need support as they get established. Through the years, I’ve used a number of time-tested methods for keeping everything in place through the maturation process – and developed a couple of my own.

[ ] Broken concrete. I particularly like to use broken concrete to stabilize a slope because it lets me create mini-planters at one or more levels from the top to bottom of the incline. I’ll set them up in half-moon shapes and have included up to three levels, depending on the extent and degree of the slope.

These little outcroppings offer a very natural look and, more important, slow down any runoff, which gives the plants more time to take up water and nutrients. In time, these features blend seamlessly into the maturing landscape.

Broken concrete can be used to create stable planting areas on slopes, from smaller planters for single shrubs to larger arcs that contain and sustain many plants. As plants mature and fill in, the concrete effectively disappears into the landscape and takes on the look of a natural rock outcropping.

I typically think of using broken concrete when I know my clients are having an old deck or patio demolished as part of new construction or a remodel. If it’s salvageable (which is usually the case), the decking can easily be broken up and put to new use – which saves your time and your clients’ money. Recycled concrete is a versatile material, and you’ll be surprised how much of it you can use without the slope looking like a stone yard.

I’ve had a few clients balk at using broken concrete in this way, even after I explain to them how their plants will struggle without this sort of planter structure. Once a first planting has failed, they typically agree to try the broken-concrete barriers. Within a few weeks – with care and some fertilizing – they see the benefits.

[ ] Conventional planter materials. I’ve been very happy with the results I get with broken concrete, but there’s a range of other materials perfectly suited to this sort of application.

You can also use flagstone, bricks or railroad ties, for example, and building supply yards offer a host of other materials that will work. Whatever you choose, the important thing to consider is that some downslope erosion is bound to occur and whatever material you use must be placed in such a way that it will be stable. Placing a ground cover or some other soil-binding plant directly below the planter will help.

As a rule, the more mini-planters you create on a slope, the more stable the slope will be. As the plants get more established, they’ll bind the soil better with their root systems. Planters also allow you to place fertilizers at the base of the plants without fear that these expensive treatments will run down the slope the first time you water. In fact, the planters create natural wells around the bases of the plants that hold the fertilizer and allow it to percolate in as water collects and soaks in.

[ ] Jute. I’m certain many of you are familiar with jute as a slope-stabilizing material. Jute is a natural netting material that, when laid across a slope, slows down water runoff and acts as a stabilizer while plants are getting established. In time, the jute biodegrades and disappears into the soil.

Jute also works as a deterrent to animal destruction of landscapes, as was discussed in this space in the January 2002 issue (click here). More than that, jute acts to shelter tiny plants that would otherwise have a very difficult time collecting enough water and nutrients as they slowly establish themselves.

[ ] Terracing. A more elaborate method for addressing slopes is terracing them with concrete-block walls. The options here are endless, but you need to know the engineering distinctions between walls suitable for casual terracing and those required for true soil retention.

In my area, anything less than 42 inches in height doesn’t require permitting.

GOING GREEN

You can, of course, cover and stabilize your clients’ slopes using nothing but plants.

If you choose this path, you need to keep the degree of the slope in mind and avoid asking plants to do the impossible. If the slope is suitable, the process boils down to finding plants that will bind the soil properly.

Generally speaking, that means using a low, thick mat of ground cover on as much of the slope as is needed to slow down the runoff – usually interspersed with other plants to break the visual monotony.

Sprayed-On Greenery Have you ever driven down the freeway or by a large slope and seen something that looks like someone took a can of blue/green spray paint to it? That’s hydroseeding. It’s a planting technique that involves spraying a mixture of seed, nutrients and water through a system that oddly resembles a gunite rig. It’s used to seed large lawns in new construction, but it’s also useful for large sloped areas that need full coverage but that would be difficult to cover with individual plants. Used in combination with jute, hydroseeding provides full coverage quite quickly at a fraction of the cost of other planting methods. And you’ll be surprised at the array of plants you can hydroseed. — S.R.

Ground covers such as Irish or Scotch Moss, Zoysia Grass and Red Fescue are all good choices for this situation, but these are just some of the possibilities. Indeed, ground covers come in all shapes and sizes, some staying within a couple inches of the ground and others that can grow to be several feet tall. The important thing to consider is how much you need the ground cover to work as a soil stabilizer around the watershape.

With a recirculating stream, for example, keeping soil from washing into the water (even in small amounts) is critical to the health of the system and its equipment – and this is true whether the underlying slope is naturally stable or not. Here, you want to plant materials that won’t infringe on the stream as they grow, that can be maintained easily, and that will bind the soil enough to prevent movement.

Using a clumping ground cover in these situations (as opposed to a trailing one) makes the most sense. In fact, trailing ground covers spread by underground runners and tend to be invasive, so you even need to be concerned about dislodging the liner. Also, trailing plants require more maintenance than do clumping varieties.

Around swimming pools, there’s the added consideration of hardiness: The plants will need to be able to withstand a trampling and cope with the occasional splash of chemically treated water.

In any given space, however, it’s unlikely that all you’ll be planting will be ground covers. I, for one, almost always endorse interspersing shrubs and perennials with ground covers to add interest to the design. (An exception would be an ultra-contemporary landscape with stark plantings and lots of straight lines.) Whatever your choices, make sure the plants address any stabilization or safety issues while enhancing overall aesthetics.

A final note: Given the fact that water runoff is a big issue with slopes, one way to combat the problem is by installing a micro-spray irrigation system. These “sprinklers” shoot out a much finer spray than do conventional irrigation systems, and at a much slower rate. Water soaks in better because there is less of it to accumulate and run downslope.

Next time: More choices for addressing sloped settings, with details on which plants work best under various circumstances and soil conditions.

Stephanie Rose wrote her Natural Companions column for WaterShapes for eight years and also served as editor of LandShapes magazine. She may be reached at [email protected].