Best way to build back up an eroding hill

Question

I will get some pictures up later tonight, but my back yard has about a 30-40 degree slope from the driveway down to the relatively flat part of the backyard (past which is a stone wall before a drainage ditch before my back neighbor's yard. Recently, I noticed a bare pipe on the slope, probably uncovered by slow erosion, which I think goes to a drain. Obviously, I want to cover it back up, but I'm inexperienced with landscaping, and it feels like dumping a bunch of soil over the area is just going to smother the grass and then erode away. Keeping in mind that I'm probably only going to be able to put an hour or two into working on it a few days a week (combination of work, toddler, and general other drains on time), what are some good solutions to fixing that sort of a thing up? I honestly don't know much about what's underneath the grass, other than that there's at least one point where I think a different drain exits (I remember noticing more water flow coming out of it one rainy season), a rabbit den (filled with gravel and then dirt, and then let the grass grow over it) and an ant hill (I know... weird thing to mention, but we had a big one, and the area where they built it up sticks out a bit from the landscape and never quite recovered grass-wise). At the top of the hill is a section of patchy grass I've asked about before. The actual lawn is a variety of grass and other plants that aren't noxious enough to treat as weeds.

Answer 1

I'm going to take a shot at this... it's a good and a tough question.

One way to tackle the hill is a retaining wall, or a series of retaining walls to walk down it. This would also require one or more staircases to give access to the lower yard. Such a solution is not something an amateur can do and will cost tens of thousands of dollars. Drainage would also be a consideration here, as you don't want to negatively impact your own or your nwighbors' properties.

The grass and other plants on the hillside are working to hold up the hill as best as they can, but they have shallow roots. One thing you could do is plant shrubs - a lot of shrubs. Shrubs have much deeper roots than grass and would do a better job of keeping the hill from eroding. There is an issue, though - how to keep the soil around the snrubs - and any mulch used - from simply moving downhill during heavy rains? One solution is is with terraces.

By "terraces", I mean plant-specific mini-walls. For example, if you were to get some large cobbles (say, 8" x 12") and partially sink the into the hill just a few feet below each shrub. This would allow you to give the shrub a flat surface and also prevent the soilmulch from floating downhill. Here's a photo of what I mean - in this case, with old and ugly pavers:

This mini-wall is only four feet wide; the hill continues on both sides of it. Note that the pavers interlock and are staked into place every few feet.

Here's an example of a mini-wall with cobbles (in this case, acting as a mini-retaining wall):

In this case, no staking is needed if the cobbles are big enough and buried deeo enough. Note that there are two levels of cobbles used in this wall.

Assuming you like this idea, then which shrubs to use? Ones native to your area are always a good idea for birds and pollinators, and ones that like good drainage because they'll be on a hillside. Some shrubs, like arrowwood viburnum, sweetspire, summersweet, and the non-native forsythia, also sucker and forms small copses; these will also help hold the soil.

Another thought... Tall grasses have deeper roots than short grasses. For example, Little Bluestem, a grass of the prairies, has roots that can grow six feet deep. Many other prairie grasses - and some forbs like Liatris pycnostachya, grow at least that deeply. You could plant these grasses on the hillside. They would out-compete the lawngrass and low weeds over a few years. I would start with plants, not seed, in this case. One issue would be how to provide access to the lower yard? I would use a staircase in that case (probably off-center and meandering a bit for design interest). This would require professionals to install and could wait at least a few years.