Installing New Sod and Amendments

Asked February 4, 2013, 11:42 AM EST

I am hoping you can assist me with a turfgrass question. I recently bought a home and the grass is perpetually soggy even though I haven't watered since October. I was told this is largely due to the heavy clay soil retaining water and the lack of drains in the yard. I've interviewed several landscapers who have given me different proposals on how to remedy the problem (all recommend installing drains). Some landscapers suggest cutting up the existing sod, adding amendments to the soil then laying the new sod. Other landscapers suggest mowing the existing grass to a very very short length, applying Roundup to kill the grass, wait several days, till the old grass into the soil, apply no amendments then lay the new sod. In the latter approach the landscapers have advised the old grass will serve as an amendment and will prevent taking away some of the top soil when the old grass is cut out and removed in the first scenario. Do you have any thought on which approch would be better?

Alameda County California sod grass horticulture

3 Responses

A first question would be: Does the EXISTING lawn consist of any undesirable or weedy grasses? If so, sod removal (scenario 1) is likely to leave behind enough of the old grass that it will grow back - along with the new sod. If undesirable or weedy PERENNIAL grasses (bermudagrass, quackgrass, kikuyagrass, etc) are growing in the current lawn, then the use of glyphosate (Roundup) to control them prior to resodding is essential.

Obtaining control with Roundup/glyphosate is more difficult than the second landscaper suggests (whether you go with scenario 1 or 2). To effectively kill perennial grasses (weedy or desirable), it is best to NOT mow the grass "short" before applying the herbicide (the more leaf area, the better the control will be). Also, complete kill will take more than "a few days". The best results are obtained by making two applications of Roundup, about 10-14 days apart. Total kill of the existing grass may take, in other words, about 3-4 weeks.

As for scenario 2 (assuming the grass is totally killed using Roundup...see above...), incorporating killed sod into soil is not as easily accomplished as you might think. It depends on how much grass is present, how much thatch is in the killed turf, the species of grass, etc. It can be VERY difficult to thoroughly incorporate killed grass into soil by tilling.

For lawn renovation using sod, the general recommendation is to kill the existing sod and remove (using a sod cutter) a very thin layer of the surface. This leaves most of the topsoil intact and provides a good rooting medium for the new sod.

For renovation using SEED, killing the old sod followed by heavy aeration (coring) - and then followed by overseeding - is an acceptable and rapid way to renovate an old lawn. In this scenario, the dead turf is left intact - where it acts as a mulch and seedbed of sorts for the new seed.

Refer to this fact sheet for additional information on lawn renovation:
http://www.ext.colostate.edu/pubs/garden/07241.html

Good luck!
Tony Koski


In the case of lawn renovation using sod can I ask what the value is of killing the existing sod before removing it with a sod cutter rather than removing it with a sod cutter while it is still alive?

Hi Eric, If you are replacing bluegrass with bluegrass…or bermudagrass with bermudagrass…and there are no perennial weedy grasses present, then it is OK to simply remove a thin layer of the sod and then prepare the soil – knowing that you are leaving behind parts of the former grass that will produce new plants after the new sod is planted. Depending on the species of grass now growing there, it may be easier to till the soil after removing the existing sod than it would be to kill the existing sod and try to till in the killed grass. Without seeing your existing lawn in person, it is difficult for me to say for certain. I hope this clarifies my previous answer? Basically, if the lawn is to be replanted with the same grass (using new sod), then there is probably no reason to kill it with Roundup before cutting it out with a sod cutter. Thanks, Tony