tilling vs topdressing

Asked July 18, 2018, 10:53 AM EDT

I am redoing my back lawn because the soil is very uneven and has hard lumps. The plan was to apply roundup, till it, let it sprout and do a second roundup application. Then we would add 3" of soil amendment and till it in. But because of difficulties getting a large tiller into the back yard, I am now considering just doing a top dressing with 3" of good topsoil after I burn down the existing lawn. The existing soil structure is quite mature, drains well, and grows everything well, so I believe new roots could penetrate it well and drainage would not be a problem if I don't till it. I am concerned about being sure I kill all that is there now and being sure I don't get sprouting of new seeds under the top dressing. How can I be sure that nothing sprouts up from the old soil layer? Can I add a layer of Preen before adding the top dressing? Or can I use Roundup with an emergent inhibitor without affecting the new seed on top of the top dressing? Does this top dressing approach seem feasible? Thank you, Dave.

Ingham County Michigan

3 Responses


3 inches of anything, sitting on top of soil and not worked in, is too much because the difference between the two is so great that a ‘barrier’ develops, and roots tend to not cross the barrier and develop deep enough. Water can also stop at this barrier and not drain properly. That said, there is no guarantee that the Preen or the Extended Roundup would not affect the germination of the seed.

There are herbicides available that can be applied with grass seed. See the first link below, and then search on products that contain one of these active ingredients.

You want to use techniques that are proven, by research, to result in a healthy, long lived turf. MSU does extensive research on turf for commercial and home sites.

If a tiller isn’t an option, then forego the 3 inches deep material and use 1/2 inch deep topdressing after you have prepped the soil bed. Core aeration would be one option for getting 1/2 inch topsoil and compost deeper into the existing soil.

A soil test is recommended so you know if your soil has enough organic matter or is lacking a nutrient- www.msusoiltest.com

If you haven’t seen the extensive articles for home lawns, here are some of interest——

This has chemical weed controls safe for newly seeded turf-


Main turf site-


Core aeration and more-


If you would like to compare other research, the Penn State and Iowa State lawn websites are very good, as well.

I hope you have found this helpful. Thanks for using our service.

This was very helpful, but it doesn't solve a key part of the problem. The lawn has hard lumps everywhere and has several depressions and holes that are up to 6" deep. 1/2" top dressing will not adequately bury the lumps or fill the holes.
I will start with a soil test to see what we can do with the soil that is there now, but do you have any suggestions for dealing with the difficult physical structure of this lawn. We'd like to end up with something that is soft and nice to walk on.
Grass, and weeds, grow well now and seem to have strong roots, but that alone does not provide us with a pleasant or safe lawn. Thanks again, =D

Sorry, Dave, I forgot about the bumpiness.

If you have 6 inch deep holes this indicates some type of wildlife present, such as moles or groundhogs. If those aren’t controlled the holes will continue. Rototilling amendments in would help greatly, and you may want to temporarily open a section of fence ( if fencing is what prevents the rototiller getting to the yard). Aeration will still help with bumpiness. Also, this bumpiness may have developed from soil with too little organic matter to ‘soften’ it. About 5% organic matter is what you want. A soil test will indicate the percentage you have now. Once you are mowing the new lawn, mulching the clippings into it will help add and maintain organic matter.

Rolling the lawn to get it smoothed out is a good option, though it can compact the soil too much. Don’t roll lawns if there are wet areas where rolling might actually do more soil compaction. Rolling is popular to flatten out mole tunnels and lumps and bumps from frost heaving during winter. If you roll it, consider doing the aeration afterwards.

If you must fill holes without working in amendments evenly, then you may see uneven turf growth as a result. Topping with 3 inches of material is usually followed by rolling it to firm it, before seeding. If your soil test indicates you need organic matter, consider using a part compost(20-50%) and part top soil mix as your 3 inch topdressing.

Here are some articles with more ideas-

These address rolling techniques—-



Moles and other wildlife—-



Bumpy lawns—


As you can see preparation is key to getting the lawn you want. Grass is a hardy plant and I think you will be very successful using a combination of these techniques.

Best regards, Laura