A nice, thick lawn requires healthy soil as its base, but it’s difficult to make changes to the soil once grass has been established. Most gardening recommendations include “working” organic matter into the soil through digging or tilling prior to planting, but this can’t be done once the grass has grown. So what’s a homeowner to do with an established lawn that’s in need of some serious help?
If done properly, the technique of “top-dressing,” or adding a thin layer of soil over your lawn, can improve the soil without killing the existing turf. Top-dressing addresses some common lawn problems, including:
- Low spots due to rotting tree roots, settling after underground pipe or cable installation, or erosion.
- Uneven terrain caused by winter freezing and thawing, water runoff, tunneling critters, or general soil settling over time.
- Compacted soil in high-traffic areas or low-lying places where water pools.
- Bare spots from variations in soil texture and nutrients, heat, drought, or other environmental damage.
- Depletion of nutrients due to leaching, neglect, or repeated use of chemical fertilizers.
Top-dressing gradually improves soil over time. As organic matter breaks down, it filters through the existing soil to improve texture and overall health. Top-dressing can:
- Improve drainage and drought-resistance
- Even out the terrain
- Reduce the need for supplemental fertilizers
- Transform your lawn into organic, low-maintenance, healthy turf
When to Top-Dress
Ideally, do it in early fall or spring since you’ll want to give your grass time to grow through 3-4 more mowings before severe heat or cold, especially if you are overseeding. It can be done all at once, or in stages. I know one meticulous gardener who top-dresses small patches as he finds them, whereas I brought in a truckload of top-dressing mixture and had an autumn marathon.
Top-dressing involves some physical labor, but the process is really just a few simple steps:
Step 1: Aerate
Lawns should be aerated every 2-3 years, and if yours is due, start with a nice core aeration. Core aeration removes plugs of soil from the ground and leaves channels for air, water, and our top-dressing mixture to penetrate the surface. For more information, see our article on Adventures in Aeration.
Step 2: Prepare Your Top-Dressing
You can make your own top-dressing using a mixture of:
- Sharp sand (not sea sand which contains lime)
- Loam or topsoil (a fine crumbly soil that is neither clay nor sandy)
- Peat (or compost if your soil needs a nutritional punch, but be prepared for sprouting weeds!)
For average loamy soil, mix these three ingredients equally. For applications on clay soil, reduce or eliminate the loam/topsoil. For sandy soil, reduce the sand. Your ingredients need to be dry and sifted until there are no clumps larger than ¼”.
Another option is to purchase high-quality top-dressing mixture or bagged lawn soil. Check with your local landscape supply yard – they often have a blended topsoil mixture on hand. While you won’t be able to guarantee the proportions, it’s economical and sold in bulk.
Step 3: Apply Top-Dressing
Now you’re ready to get started. Working a few square feet at a time, shovel out a small mound (maybe 2-3 shovelfuls) of mixture onto your lawn.
Spread the soil using something flat, like the back side of a heavy garden rake, working it into aeration holes and covering low spots. Make sure the top-dressing is no more than 1” deep (preferably ½” or less) over the existing grass.
Keep working the mixture until your grass peeks through and the depth is even. I like to flip the garden rake back and forth from the flat side to the tine side, carefully combing the grass to get the top-dressing mixture settled on the soil surface.
For low spots requiring more than a couple of inches of top-dressing, first remove the existing sod to prevent underground decay that can damage new grass seedlings. After filling in the low spot, either replace the old sod or re-seed the area. You can also address deeper spots by adding a couple of inches of top-dressing each year, slowly building it up over time.
Step 4: Water and Adjust
At this point you’re technically finished, but in my experience a good top-dressing mixture does some settling. I would recommend watering the area well (or top-dressing before a nice rain), letting the mixture settle for a day or two, then go back with your rake and smooth out any little hollows or bumps that may develop.
Step 5: Plant Grass if Needed
Now you can replant grass in any bare spots. Existing grass should be able to grow through as much as an inch of top-dressing.
How Often to Top-Dress
Trouble spots may need repeat applications, but regular, uniform top-dressing does not need to be an annual tradition. Keep in mind that you’re adding soil, which over time will raise your grade and affect thatch breakdown and soil ecology, so don’t go overboard. Plan several light applications for troublesome yards, rather than one deep one. For overall organic soil amendment, a very light application of top-dressing brushed into aeration holes can improve the soil without raising the grade.