By Victoria Torley

Well, the other day we went to see the home a friend is building and he had a lot of questions.

The house in progress is a custom project with wide windows and spectacular views of Lake Arenal and the Arenal volcano. His problem? Erosion control.

Like most homes around the lake, his is built on a hillside. On one side of the house, there is a sloped bank about 3 or 4 meters tall that is already (poorly) terraced. His pool is next to a slope and the area for a guest house is sloped on all sides. Hmm. Erosion control? How about control of slumping and subsidence? 

The initial recommendations are as follows: For a 33% slope (1 foot of elevation for every 3 feet of horizontal distance), plants can be used for erosion control. For a slope of 50%, a retaining wall is required.

So, our friend has a double whammy. At the side of the house where the property is terraced, he will need a retaining wall or the neighbor's property will slide onto his. He will also need a retaining wall near the pool. At the guest house platform, which is not going to be developed in the near future, he needs plants to prevent slippage.

Let's begin with the easiest slope, the one around the guest cottage platform. Why is it easy? Even though the slope is more than 33%, there is one grass that can handle it,  Chrysopogon zizanioides or vetiver, which can put down roots 3 to 5 meters deep. While not the most attractive of grasses, it will hold and maintain the slope until our friend makes a more permanent decision. Since it is a sterile grass, it won't rampage through the countryside.

For that neighboring slope, he may want something bright and interesting. No problem. First, he will need rocks, big ones bordering on boulders. They will need to be dug into the hillside and plants put in immediately. Perhaps succulents are best, a lot of succulents, all types, all colors, all heights. They will make a veritable hillside mosaic. The boulders for stability, the plants for color.

For that last slope, he can use the same technique with boulders or go with perennial peanut, or maní. Maní is an excellent choice although if he wants to change it later, it is hard to remove once established. Another choice is Wedelia triloba, or wedelia, which also has deep roots. Both plants put down very deep roots and both will cover a hillside quickly.

 

So, my friend, this column is for you and all the others who are looking for something to plant on a hillside.

Plant for the week. Wedelia (Wedelia fructicosa) is a genus of flowering plants in the family Asteraceae. They are one of the genera commonly called "creeping-oxeyes." The genus is named in honor of German botanist and physician Georg Wolfgang Wedel (1645–1721).

Why Wedelia? Along with its ability to help stabilize hillsides, the plant will produce a mass of yellow flowers when planted in full sun.

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For more information on this article or about gardening, Ms. Victoria Torley, a gardener columnist, can be reached at victoriatorley1@gmail.com