Put soil for new lawn on existing grass, is it a problem?

Hello, everybody,

I decided to make new lawn. I poisoned grass and weeds using Resolva (the seller in the shop told me that Resolva I bought worked only throguh leaves, therefore it does not stay in the soil and I can establish lawn immediately after weeds die, most weeds died in 2 weeks time), cut the grass, removed cut grass and moss, then put 3-4 inches of new top soil. However, I read that I should have removed all grass including roots completely before I started putting new soil. What will happen if I leave as it is and put turf? Will there be a serious problem? Thank you.

 

Hmm..

The roots of the turf will have a hell of a problem growing through the old grass.
When you lay turf on bare ground you still need to press it down firmly to give the roots a chance to "take."
Even on well prepared soil, sometimes parts of the turf doesn't take and dies off if it hasn't been pressed down enough..

 

Do the roots of the turf go that deep, 3-4 inches beyond its layer? I thought roots are about 2 inches maximum...

 

Quick answer, roots will go to varying depths depending on the grass species and the growing conditions (a lot further than 4 inches). What is the quality and consistency of the top layers of substrata of the lawn which you've covered?

The deeper the roots go the better prepared the lawn is to cope well with drought conditions.

 

I think it is clayish, a lot of cracks because of lack of rain.

 

Effectively then you have a hard pan of sun baked clay 4 inches below the surface of your lawn and on top of this is the now decomposing vegetation from your old lawn. The new roots will have a hard time penetrating this pan and water will also tend to stay at this level. You may experience water logging from late autumn through to early spring and in times of dry weather as the moisture becomes sparse the grass plants will be unable to provide themselves with enough water to cope and your lawn will suffer and require watering to maintain it's health. One extreme to the other.

Are you able to move the soil from one half of the area to the other and dig over the ground underneath or is that unfeasible now? If it's feasible you could add a measured quantity of lime to the surface of the old lawn which would help break down the clay below. Even just digging over the old lawn surface and adding some sharp sand would be beneficial.

 

Thanks for advice. I think now it is too late.
By the way, the dried old soil created a lot of cracks on surface, so a lot of new soil fell into these cracks. I was quite surprised how many of these cracks I had - perhaps average distance between cracks was less than one foot and cracks were deep. About 25% of my old lawn was grass, the rest was moss which I removed before laying new soil. New soil has a lot of gravel and sand to improve drainage.