How much topsoil to grow grass

15 years ago

I want to extend my backyard out a little. I have a french drain that is covered in crush stone that currently marks the perimeter of my lawn right now. I want to excavate some of the stone, put down some landscape fabric, and then put topsoil on top and plant more grass so it's level with the rest of my yard. The other option is going over the top with soil where it is now but that would take up a lot more, be more work, and change the entire grade of my backyard.

How thick does the topsoil layer have to be? I think I might be able to get 6" of topsoil there right now. Is 6" enough for grass to grow?

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Comments (11)

bpgreen
15 years ago
Is landscape fabric that stuff that blocks weeds from coming up but also blocks roots from going down? If so, 6" is probably a minimum. I've dug down a foot or more and still found strong grass roots. That was with KBG and/or Fescue.

Why are you putting down the landscape fabric? With 6 inches of soil, it's not likely that any seeds will germinate and grow through the 6 inches of new soil, is it?
paulinct
15 years ago
I think he is doing that to prevent the new soil from immediately dropping lower into the gravel and sand, which I think is a good idea to keep the septic system working for awhile, but eventually I imagine that it will all drop down there, and the septic may fail. Having a septic system myself, I don't see any alternative.
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I mostly agree with texasweed in hesitating to till. I realize you can find hundreds of articles on that topic, but you will never find a reliable landscaper that tills before installing a garden. They always use a tractor and box blade to develop perfect drainage and seed bed. If you are in a new development, your soil was probably graded already. If you add more soil you are almost guaranteed to ruin the drainage. If you end up with water draining into the house, you are in for a long time of headaches. I'm am assuming you don't need more soil. No matter what soil the contractor left you with, it is adequate to start a lawn. Pure sand is what I use as a replacement for my lost topsoil. Sand will never be "topsoil" but it works great for grass. Removing the rocks is a good idea, but I would not go way overboard on that either. My bedrock protrudes from the surface in places and is as much as 18 inches deep at the deepest. You can't dig holes in my garden without a pick or jack hammer. But I digress. Whatever soil you are starting with is fine. It will become topsoil before you know it. As for seeding, the most I would do, assuming your soil is properly graded from the contractor, loosen the very top with a leaf rake, apply a mix of Kentucky bluegrass seed and turf-type tall fescue, roll it down with a water filled roller, and water. KBG takes a little longer to sprout than fescue so keep watering daily until the KBG comes in. Set your mower to the highest setting and mow when the grass is tall enough to be mowed. Back off on watering frequency as you can but increase the time you water. Eventually you should be watering every other week unless your part of WA is in the desert. Then during the hot part of summer you might need to water weekly. Fertilize after you have mowed the grass for the second time. You don't add weed killer unless and until you have weeds to kill. Don't worry about not having weeds. Spring seeded lawns are very susceptible to crabgrass sprouts. Keep your grass growing up tall and that will help keep the crabgrass out.
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bpgreen
15 years ago
Paul--Maybe I missed something, but I didn't see anything about a septic system.
paulinct
15 years ago
No you didn't, it was me.
parafly9
Original Author
15 years ago
No septic system. I want to take the crushed stone from the top and fill it in with dirt. So underneat the dirt will be landscape fabric and hten about 2' of crushed rock. I was wondering if 6" was sufficient to grow grass on.
dchall_san_antonio
15 years ago
Six inches of soil is plenty, BUT...please explain why you want to use landscape fabric. Nobody uses landscape fabric under turf, so I'm wondering why you think you should.
parafly9
Original Author
15 years ago
I'm putting it on top of the french drain to prevent it from clogging fast. You are supposed to apparently from what I've read online. IN other words i have a 12" trench of rocks and landscape fabric on top, soil on that, then grass.

This prevents the soil from going into the french drain and clogging it up.
karensson
15 years ago
I understand what you are trying to accomplish, the optimal way of doing this would have been to use the fabric sleeve that go around the entire pipe because it will be difficult to ensure that the fabric stays in place anyway.

If you have an opening through which to clear blockages(i.e. run a snake through ) your best option may be to make sure that the river rock in the trench is compact and in place and place top soil over top of it lightly and spead you seed. The grass will cover the trench soon enough without a lot of work and time that might not get you very much benefit anyway.
parafly9
Original Author
15 years ago
I think the pipe is in fact wrapped in filter fabric.

anyways, it's already done. The dirt is down over the drain so :)
karensson
15 years ago
If the pipe is wrapped in fabric then there isn't or in this case wasn't a need to put the landscape fabric over top.
grabbag
12 years ago
i too want to grow grass, above ground on my Terrace, which is composite (plastic) boards with a 1/4" gap between that floats about 6" above a flat membrane roof which is all new construction. i was thinking that i would lay down a root barrier fabric, then a moisture mat and build it up with dirt to 7" to then grow my grass.

is this a sound plan?

How much topsoil to grow grass

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bpgreen

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How much topsoil to grow grass

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