Dealing with Sod & Persistent Weeds

Sod is the matted, entangled roots and vegetation of grassy areas. It makes adequately working the soil extremely difficult. Also, any of its remaining clumps regrow easily, creating a weedy mess that competes heavily with garden plants. If it’s growing on your prospective garden plot—in the form of an existing lawn, for example—destroy or remove it before you work the soil.

Persistent weeds are those that have large taproots (like dandelions, bull thistle, burdock, and Queen Anne’s lace) and grasses that spread by strong stolons and or rhizomes (like quackgrass and bermudagrass) that allow these plants to work their way to the surface through several inches of soil or mulch.

To rid your plot of sod or persistent weeds, you have three options:

The Methods

1. Smother Them

If you have enough lead time, the easiest option is to smother the sod and/or persistent weeds. Smothering is an excellent option, because, not only does it take less bending and lifting, but, if you start it far enough in advance, the surface vegetation and mats of roots also sufficiently degrade into the soil, making your later soil working processes much easier and the home for plants much healthier.

Three-to-six months of smothering works for most sods. However, since especially persistent sods and weeds can take nine months to a year to fully suffocate, a year or more is even better (if you have the time). Plus, if you wait this long, you’ll be adding fertility to the soil instead of (temporarily) taking it out.

While they’ll slowly release it back to your plants along with all other essential nutrients in perfect proportions as the decay process continues, the microbes that decompose organic matter—in this case, the roots and vegetation from your sod and weeds—fuel their process with nitrogen, tying lots of it up and making it unavailable to your garden plants during the early stages of the decay process. Plus, the roots of many plants, especially sod-forming lawn grasses, form dense mats with their surrounding soil, making it difficult to till or for the roots of new plants to get established until they’ve decayed. If you smother the sod and weeds nine months to a year beforehand, however, the vegetation and roots have sufficiently degraded so that they are now adding nutrients and organic matter to the soil, and the soil is much looser and more friable, making it easier to till or for plants to root into.

To smother the sod or weeds, you can use just about anything that covers a large surface area—cardboard, tin, tarps, thick black plastic, old carpet, or whatever you have or can easily get. Be sure to weight your material down so it doesn’t blow away. If you use multiple pieces to smother an area, just overlap all edges of your material enough so no grass can find its way through and grow up between them. Six-to-eight inches is generally enough overlap, but it depends a little on the material used and whether or not you weight its edges. Then just sit back and wait and let nature and decomposition do the work for you.

2. Dig or Cut Them Out

If you don’t have sufficient lead time, you can dig out the weed and cut out the sod. There are specific walk-behind sod cutters you can rent that cover large areas in a short amount of time. You can also use any form of heavy equipment—although I’d recommend against it for the compaction damage the “heavy” part of the equipment does to your garden and their lack of finesse in removing only the thinnest layer of topsoil. Most of us, however, will end up using a shovel. The process is as simple as it sounds: You dig the sod out. There are some methods, however, that are a little easier than others.

The easiest commonly-owned tool for digging sod is a garden spade. Its flat blade allows you to cut straight lines and easily cut under the sod to remove it from the deeper soil. Start each spot by cutting the area’s entire perimeter straight down about three-or-four inches deep. Next, divide and cut this larger area into square or rectangular chunks of sod you can realistically move. Along one edge of each smaller chunk, insert the blade and pull back on the handle, lifting the edge of the sod out of the ground an inch or so. Then, use that lifted, exposed edge as a starting point to cut the top inch of sod from the deeper soil. Once it’s completely released from the lower soil, lift that chunk of sod out, folding it in half or thirds if necessary, put it in a wheelbarrow or garden cart, and move it to your compost pile to recycle the great fertility and masses of microbes of this top inch of soil.

A digging fork is often the best tool for digging out persistent weeds, stepping it into the soil and prying back on the handle to loosen the soil and partially pop the weed out of the soil. For some deeply-rooted rhizomatous grasses, this will take significant prying, gently pulling and exploring with your fingers, and prying again before stolons or rhizomes break. It can be a tedious task that will make you wish you’d smothered them or turn to tilling them in.

3. Till Them In

If you don’t have sufficient lead time, you can also till the weeds and sod in. If you choose to till them in, make sure you make enough passes to completely pulverize the sod or weed roots, not just break the sod up into clumps or leave whole weed roots intact. If it doesn’t look like a smooth, well-tilled bed, it won’t act like one. Any pieces of sod or whole weed roots will resprout if they aren’t sufficiently chopped up and mixed in, creating an unnecessarily weed-filled headache. Too much tilling isn’t good for garden soil, but this is one time it’s better to err on the side of a little overkill.

Smothering the area with cardboard, a tarp, or the like for six months or more beforehand makes tilling in the sod and weeds much easier. The longer the better since the dead vegetation and roots become increasingly broken down over time so are more easily tilled into the soil.

Words of Experience

If You Have Enough Lead Time, It Seems Smothering Is Easiest

After years of digging it out, getting as much topsoil out of the roots as possible, and composting the remaining roots and tops, we’re now fans of just killing it via smothering. It’s much easier (and easier on our backs), and, if let to sit under its covering long enough, the sod is so broken down that it’s easy to till or fork in, keeping all that topsoil and organic matter right there without getting cycled through the compost pile and added back.