A worried rain garden winger . . .

l pinkmountain
5 years ago

I'm kind of winging it here with a rain garden design, I know just enough to get myself into trouble. A colleague with landscaping experience is helping me but I feel like I need to get more sets of eyes working on this. I'm constructing a rain garden to absorb runoff from an adjacent service road onto an arboretum hillside. At one point, a french drain was already draining water from the steep slope adjacent on the left, into this area and erosion wasn't a huge problem. Soil is sandy gravel from an old pit. There were telephone poles and wires running through this area so trees were cleared and soil was piled up and old asphalt was dumped around. It was kind of an eyesore area and then the drain got plugged and we started getting erosion again. Not here, but adjacent. Then one day, the poles came down because the wires were re-routed and buried somewhere else, so the whole area opened up to new and improved landscaping possibilities! Plus I got a grant to do it.

We've graded out the piles of dirt and redone the drain tile so it ends right in the middle of this hill, and now I'm designing and planting the area as a rock garden and series of rain gardens. In the photo the dirt piles will become LOW berms planted with rocks and wildflowers. I'm not too worried about size of the rain gardens or a lot of erosion, since even if I did nothing but just leave the drain, the area would serve as a rain garden. Salt flushes from the service road in the winter are an issue though.

Reading Yardvaark's critique of various hillside planting schemes, I'm worried about other issues I haven't thought of. I don't have a landscape design program so I just used "Paint" to do this primitive mock up. I welcome critiques of the plan.

I am concerned that soil might erode and build up around the existing black cherry in the right side of the photo, but it is not some valuable tree so if it dies, no great loss, there are other similar trees adjacent. I'm also thinking that the tree in the foreground in the middle of the view of the rock garden will block the view rather than be a focal point. I had initially planned on using a yellow-wood tree for that spot, and have the tree already but I'm thinking that might be a mistake.

This is a garden on a hillside that contains a collection of witch hazel shrubs which is the goal, to create an open woodland garden with flowering shrubs underneath, both witch hazel and other shrubs that would flower at other times and compliment the witch hazels. Backdrop of evergreens. Already I'm thinking I should put more junipers in the back of the plan too. Unfortunately, now I'll have to do the mockup sketch all over again from scratch since I can't "erase" just one feature out of a "painted" photo. I'd also welcome any suggestions of landscaping freeware I could use to do a better rendering.

In my posted photo sketch, the black blobs are rocks and the brown are the berms with the blue being the drainage area behind which will be filled with a mix of compost and sand, to mitigate the salt. Berms are for aesthetics rather than holding any water back, but I have never build a rock garden on a berm so I am out of my element on that too. The berm to the far right looks closer in the photo to the two trees than it actually is. I'm not particularly fond of those trees, one is a black cherry and one is a walnut, but they have utility for more than just aesthetics, so I'm leaving them for now.

Key: Black blobs=rocks,
dark green tree top=evergreen,
kelly green tree tops=small flowering trees,
light green blobs=large flowering shrubs,
dark green with white on top=small flowering shrubs,
all else is wildflowers,
blue=rain garden area,
light brown=berm,

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