Weeding and mulching septic system mound

ElzabOctober 15, 2011


Recently bought a home with a big septic system mound covered with grass and loads of weeds. It is full sun. We put in a few ornamental grasses and lavenders which look great but we need to do something about the weeding and constant mowing we need to do around each plant. Our plan is section 1/to get rid of grass and put in some low sedums or heathers (but harder to grow in this area?) as a ground cover. And back section 2/replace with a flower meadow. Apparently we cannot till or mulch due to damage risks and the importance of maintaining aeration. At this point I think we could A/just use a Weed B Gone product and cover up grass with thin layer topsoil and plant our new succulents or flower meadow accordingly. B/Use an organic biodegradable/breathable paper layer, water, cover top soil and plant. I have read every University extension paper on these septic systems and know what plants to put but am going crazy with lack of what we CAN do. Any tips on what worked for you?

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whitegarden(Z5 MA)

I would start by contacting your town's building department and asking them what you are allowed to do. No sense in guessing.

    Bookmark   October 16, 2011 at 9:15AM
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diggerdee zone 6 CT

Are you referring to the leaching fields? Or is this the area over the tank itself, which will have to be uncovered to be opened and cleaned?

I agree with whitegarden - start with the town and see what is allowed first, and then take it from there. Let us know what they say and then I'm sure you'll find help here.


    Bookmark   October 16, 2011 at 10:24AM
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I guess I am not totally clear what your goal is. Is the problem that the mound is obtrusive in your view and that you want it to look less like a septic mound? Or is this the only sunny spot and so you want flowers here? Or do you just want something tidy and easy to maintain rather than a bunch of weeds in this area?

I've lived with a septic system for 30+ years. A septic field is an expensive thing to replace and I've never wanted to mess with it much. Most folks I know just have lawn on their septic field and that is what we had at our last house. In our current rural setting, the septic is out in a field that has hay-type grass, mowed 2 or 3 times a year with a tractor and so that is what is on our septic as well. We have an old piece of farm equipment, a horse-drawn hay rake, sitting on top that we found in our woods, as sort of a joke since around here old farm equipment is often used as lawn ornaments.

Getting a wildflower meadow established is a lot of work (like any new garden) as you need to be vigilant the first couple of years to weed out undesirable plants. For both the parts of your plan, you will need to do quite a bit of weeding until plants are well established and closely enough spaced to shade out most weeds. I think that's why most folks use grass (in addition to knowing that it won't interfere with the system) since it makes a great groundcover that just needs to be mowed and is therefore less work.

In addition to WG's suggestion, I'd get a soil test done to find out if you need something done to the soil (like lime or fertilizer) to get whatever you decide to plant on the mound the best possible growing conditions. It's not necessarily good topsoil that is on your septic, so putting a very light coat of organic matter on this fall that will decompose quickly (such as an inch of chopped leaves) may help by adding organic matter. Also, with whatever you decide to plant, a light, thin layer of mulch without unwanted seed like straw will help retain moisture and provide better conditions for plants to establish while not interfering with the septic function.

If the problem is a rectangular or square mound in the center of your front yard or other view, you might want to think about camouflaging it rather than emphasizing it by planting on top of it. You could consult with an expert in building septic fields to see if the shape can be altered at all by adding soil at the edges to make it taper into the surroundings better or to make it less rectangular. Or if the budget precludes that, can you add a picket fence several feet a way on the main view side with a garden of tall perennials on either side of the fence to camouflage the change in grade rather than planting on top of the mound?

    Bookmark   October 16, 2011 at 10:35AM
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Thanks so much to those three members who took the time to respond. Yes, the mound is over the leaching field. We have already checked: It is fine and recommended to either grass or landscape with low root system plants on this area. The roots will hold earth in place. The landscaping is very common for this type of mound. It is a huge mound in our back yard and just having grass was not working for us for many reasons (we have a lot of land to mow, this area should not be mowed on that often, and for aesthetic reasons). Testing the soil is an excellent idea. It is not a rectangular mound, rather a tapered oval or bean type shape. If you saw, it you'd see that it looks very nice with the ornamental plants already there and that plus a ground cover is the way we think we should go. Thanks!

    Bookmark   October 16, 2011 at 7:54PM
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I guess I'm unclear what your question is, which is why I didn't respond sooner. After your second post, I think you are just asking about how to get rid of grass in an area where you want a bed, and it really doesn't have much to do with the fact that it's a septic field. I agree in that case that mulch including a layer of paper is the way to go.

I never bother with weed killer in a new bed, when I'm converting lawn to flowers - mulch with newspapers seems to do the trick every time.

    Bookmark   October 16, 2011 at 9:58PM
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Steve Massachusetts Zone 5b

The quickest way to get rid of that grass is with Roundup. It'll be dead in a week or so and you can go ahead and plant ornamentals. Read the label. It breaks down in the soil fairly quickly in the soil, so as herbicides go it's the one to use.

Newspapers work well, but they area lot of work and then you need to put something on them (woodchips, mulch, grass clippings or something organic).


    Bookmark   October 16, 2011 at 10:40PM
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whitegarden(Z5 MA)

Here's a link that might be helpful:


From that article, some info about "Roundup."

"� Recent research has found Roundup to be deadly to frogs and toads and to negatively affect human reproductive function.
� 2, 4-D, the other most common American herbicide, is linked to non-Hodgkins lymphoma.
� And a recent Scottish study found that use of any pesticide increases the risk of developing Parkinson�s."

The author offers some great alternatives to chemical pesticides in the article and in a related article he links to.

    Bookmark   October 20, 2011 at 8:38AM
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