Placing native plants on a grassy slope

sujiwan_gwFebruary 27, 2014

The long steep slope that is my front yard was planted with some sort of sprayed on grass seed a few years ago. It's the same stuff they used to stabilize the soils after earthmoving in this development.

It's such a steep slope that it's hard to navigate and I don't want to ever have to run a mower/weedwhacker on it . I have decided to put in native shrubs/ perennials/annuals that are suitable for sunny slopes in my MidAtlantic region. I'm going to try to work this slope in yearly increments since it's pretty long.

I'm planning to start with the woody plants. Meanwhile, how do I deal with the grass (fescue?) growing in the area of the slope I'm planting in? Only clear an area around the shrubs or remove it from the entire section to be planted?

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Some will tell you to blast the area with RoundUp...But I would prefer to use a technique called Soil Solarization.

I would consider using juniper. It's basically a no fuss, evergreen, that looks good, and excels at preventing soil erosion. I guess I would probably just solarize round 3x3 circles where I plan to plant the shrubs and keep expanding and removing each year as the shrubs mature. It will take a while for them to fill in and cover the whole hillside, so you will want the grass to prevent erosion.

You can get cultivars of Juniperus horizontalis (Creeping Juniper Groundcover) in Greens, Blues, and Yellow.

Here is a link that might be useful:

    Bookmark   February 27, 2014 at 11:22PM
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Suzi AKA DesertDance Zone 9b

Do NOT do juniper! It is the bane of my life! Some previous owner put it on our hillside, and it's killer to kill!

We are slowly doing it, but this would be the choice for my worst enemy!!

    Bookmark   February 27, 2014 at 11:55PM
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mad_gallica(zone 5 - eastern New York)

First question is how do you feel about trees on this slope? Unless you take active measures to keep trees off the slope, that is what you are going to get. Native plants are designed to just be placeholders until the trees move in. Something like spreading juniper is smothering enough to keep the trees down to a dull roar. Anything is going to require one or two weeding passes a year to pull trees.

Whatever you do, don't remove more of the grass than you have to. The root systems are stabilizing the slope. Most woody plants should be able to outcompete fescue, so clearing an area right around the plantings holes is about it.

    Bookmark   February 28, 2014 at 6:53AM
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I'm not expecting a maintenance free landscape -I'm just trying to practice conservation and restore some ecological balance.
I'll have to watch for locust and ailanthus here. Hopefully, the bulbs, perennials and self seeding annuals on the slope will fill in bare ground among and around the shrubs eventually and out-compete anything blown in.
I may need some sort of shoe spikes to keep my balance! It was a much gentler, longer slope before the developer plans were implemented around us.

    Bookmark   February 28, 2014 at 8:21AM
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mad_gallica(zone 5 - eastern New York)

Understand that what you are planning is a garden, and it will require the same level of maintenance.

    Bookmark   February 28, 2014 at 8:52AM
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I'm somewhat confused as well... If it's so steep that you need spikes on your shoes, bulbs, perennials will do nothing to hold back the erosion... and none of these planting will ever out-compete weeds... If you go this flower route, plan for a heavy maintenance burden...

You need something with roots that is going too add structure to the slope, not flowers.

    Bookmark   February 28, 2014 at 12:09PM
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I suggest you do a lot of investigation of that slope before you remove the grass. The roots of trees and woody plants can serve to stabilize a slope against slope failure, but these roots do not help prevent soil erosion which happens at the soil surface. Grass is the one cover that can hold fast moving water above the soil surface to prevent erosion.

Depending on the properties of your slope (steepness, length from top to bottom, slope imperfections, and soil type), removing the grass could result in an intolerable level of erosion. Undoing a project and reestablishing grass could be expensive.

    Bookmark   February 28, 2014 at 12:47PM
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Sorry, I was being tongue in cheek about the shoe spikes. I'm complaining that its much harder to navigate the hill than it used to be.

The similarly steep slope on the south side was planted (by developer) with 3 rows of white pines after grass had been laid down. They seem to be doing fine after 4 years. But I don't want to hide my view in front with tall trees or go the monoculture route.

I read the following on a native CA plant nursery site (link provided) when researching about planting slopes. Why wouldn't it be the same for Maryland native plants? (They really think grass is a bad idea to use on slopes. I am seeing areas of erosion on my grassy slopes.)

"A mixture of deep-rooted [California ] native shrubs, and trees, mixed with shallow-rooted shrubs, and perennials, mulched and with no weeds, will control erosion on the slope. Why should you plant a [California] native plant community on the slope and not grass or ice plant! Because the native plants connect with each other underground, and the microorganisms that live in association with them produce tiny threads that ramify through the soil, coiling around particles of sand and clay and holding them, and also producing glue-like compounds to hold the soil particles. This interconnection, I guess you could think of it as a natural microorganism community underground living in cooperation with the plant community aboveground, which the grass and iceplant, and other alien plants do not possess, is why it is critical to plant [California] native plants in a spaced plant community to control erosion on a slope.

From the San Dimas Research Experiment of erosion and hillside runoff.

"The concept that surface runoff is rare on any undisturbed watershed...has become accepted among forest hydrologists and seems equally to apply on the San Dimas experimental Forest." (Patric)

If the hillside has native plants covering it, there was no runoff and the soil slowly released the water over the season. A trace of runoff from native plant covered slopes.

Grass covered slopes lead to hillside erosion and possible landslides. 30-75% of all rainfall on grass- covered slopes ran off.

The native plant -covered slopes also stayed drier in winter. Weedy or grass cover slopes get very wet very fast and either shed water or slide mud. Iceplant, Vinca, Ivy fits the weedy role, not the native role.

So bare soil or grass (or straw) -covered slopes experience boundless erosion through mudslides (wet slopes) and surface gullies when compared to the "beggarly erosion of slopes planted in a community of native plants".

Here is a link that might be useful: How to landscape a hillside slope

    Bookmark   February 28, 2014 at 1:29PM
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I think that is spot on... native shrubs and trees will prevent erosion. Here in New England this is what is planted alongside highways and steep hillsides near roads and it does an excellent job.

Juniper was just one idea, you can plant anything you want that has a sufficient root system. I have a steep hill in my front yard as well, and have a mix of pendulous conifers, juniper ground cover, hydrangea, blue spruce procumbens, and plan to continue to add additional low grow evergreens that look good and function to stop erosion. I don't know that natives are required, but will certainly adapt the best.

You will still need to weed, unless you are going to put down landscape fabric and annual mulch cover. The fabric is also not recommended, as it looks bad when the mulch slides down and exposes the fabric... I just mulch annually

    Bookmark   February 28, 2014 at 1:40PM
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The link you provided was to an article written by a nursery, not by an engineer or landscape architect. They are in the business of selling native plants. The article is self serving and confuses slope stability (mud slides) with erosion. While the solution the article promotes can work on some slopes (more likely in an area of limited rainfall), it's likely to be a disaster for you if you are already having erosion. Every slope is different and there is no such thing as one size fits all.

    Bookmark   February 28, 2014 at 2:12PM
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mad_gallica(zone 5 - eastern New York)

I went out on the front porch and took this picture of the 'native plant community' across the street. I don't know what all is over there, but maples, oaks and ash are in the mix, as well as sumac.

If this type of thing is acceptable, go for it. There is enough root mass to control erosion. Similar plant communities grow on quite steep slopes around here. However, it should be obvious that nothing there is afraid of any dinky little grass. It should also be obvious that any similarity between that and a California ecosystem is purely coincidental.

    Bookmark   February 28, 2014 at 3:47PM
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A very difficult situation which needs understanding of the best control method. The mention of locust and alianthus weed trees presents an ever present problem, namely dense growth of both blocking native plant growth and/or the view unless some form of annual tree seedling removal is figured out. Keep efforts simple for best results.

In time goldenrod and other native flower growth may be encouraged by tossing homemade "dirt bombs" of desired native seeds (lots of information re this subject on-line) onto the slope both spring and fall for a few years.

Years of experience leads me to suggest that in the late fall after all has gone to seed a 'mountain goat' in the form of a mow 'n blow firm be retained to weed whack all growth back on the slope annually. Pay the bill. An easy method which should give desired results.


    Bookmark   February 28, 2014 at 8:14PM
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Remove as little grass as you can, and cover the area around the new plants with several layers of newspaper and mulch to keep the grass out.

Lay out your desired finished plant pattern. Work across the hill in manageable strips and irregular bands of your new stuff and let the old grass serve as erosion control and groundcover until it can't compete.

It's easiest of you complete one strip at a time so you aren't having to work around the older plants while adding new.

    Bookmark   February 28, 2014 at 8:28PM
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