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Wednesday - April 08, 2009

From: Woodstock, VA
Region: Mid-Atlantic
Topic: Erosion Control, Grasses or Grass-like, Vines
Title: Stabilizing a shale slope in Virginia
Answered by: Barbara Medford

QUESTION:

I have family members who recently built a new home in Virginia. The site required extensive excavation resulting in a large 30 foot, nearly vertical, shale wall behind the house. They now want to revegetate the wall to reduce crumbling. With a southern aspect and very little, if any, soil, moisture retention will be at a minimum. I have suggested training native vines, such as Virginia creeper and Trumpet vine, to grow from either the bottom or top of the wall. Any other suggestion for this difficult situation?

ANSWER:

We have previously answered a similar question from Pennsylvania, and have excerpted some of that below, and then added comments relative to your particular situation.

We think that before you start trying to find plants that can survive on that slope, you need to make sure it is safe. We have a few questions to ask that may send you in the right direction, because we really can't recommend any plants that would grow in that shale unless there was at least some soil on top of it. Our first question is: Has the slope been examined by an engineer or a geologist to ascertain if it is stable? Is your house sitting at the foot of this bank? Are there other properties in your area with a similar situation, and have you observed the solutions those landowners have reached? Probably our first question is the most important. We are gardeners and not civil engineers, but especially if the house is at the bottom of the slope, hardscape measures, like terracing and retaining walls, need to be undertaken right away, managed by someone who knows what they're doing. This would be an expensive proposition, but not as expensive as having the slope in your living room after hard rains. If the slope is down from the building, that is not quite as imminent a danger, but certainly should still be examined to make sure the foundations are not going to be subject to de-stabilization from erosion down that slope. 

If there is some soil on top of the shale, there might be grasses that could be coaxed to grow there, but nothing planted is going to hold that slope if it begins to slip. Even if there were some soil (and water could be made available to the plants), how on earth could anything be planted? Hanging by your fingernails from the cliff while you dig a hole and put in a plant is probably not an option. Your suggestion of Parthenocissus quinquefolia (Virginia creeper) is a good one for covering the slope, in that it climbs by use of adhesive disks which permit it to cling to walls or rock. It is native to Virginia and can grow in sun, part shade or shade. Campsis radicans (trumpet creeper) might not be so effective, as it climbs by aerial twining rootlets. Without something those rootlets can twine on, it wouldn't go up, but might go down, if planted at the top and cared for. It is native to Virginia, also, but remember that it can be undesirably aggressive in the South, and might decide to take off on its own, instead of dealing with that inhospitable shale, and could end up in yours or neighbors' gardens where it isn't wanted. It requires full sun. 

 

 

 

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