Q.I have been told that it is okay to install a new turf lawn over what remains of an existing turf lawn. I understand that when the old lawn is covered with a soil/sand mixture and aerated that it will just break down and form a suitable foundation for the new turf to grow upon.
Our original turf lawn was installed about 18 years ago. It is now mostly moss with some exposed areas of soil. The winter was very wet and cold, causing some areas of grass to die off entilely. Will a new turf lawn bond properly and grow sucessfully on top of the old lawn underneath?
(B.C, 1 June 2009)
A.The general agreement amongst gardeners seems to be that laying new turf over an existing lawn would be likely to cause problems with the new grass forming its proper root structure, but having said that, there are some remarkable success stories – admittedly mostly from the US – which suggest this method can work really rather well. I suppose the answer to your question depends on who it was who told you about the idea – and if it was a professional landscape gardener who’ll back his or her words with a proper guarantee of the work, then you have to be on to a winner!
For most new lawns, however, the traditional approach of preparing the site before you lay turf is almost certainly the right way to go.
Prepare The Site
The usual rule of thumb when it comes to any new lawn – seed or turf – is that for success you need to allow three months from the start of site preparation before laying or seeding to allow the soil to settle, and the first part of that involves getting down to bare earth. This can be a long and laborious job if you’re clearing rubble or tree stumps, but since you’re planning a “new” lawn where there’s already an old one, hopefully this stage will be limited to a little judicious use of weed-killer to see off the moss and perennial weeds.
Depending on how flat your existing site is, now is the ideal opportunity to grade the ground to remove any undulations, or lumps and bumps that exist. The new lawn doesn’t have to be spirit-level flat – a slight slope from one end to the other helps drainage – but it obviously shouldn’t look like a ploughed field!
If you do need to level the site, it’s better to buy in topsoil to make up the hollows rather than risk exposing subsoil by digging down the humps; if your topsoil layer is less than around 15cm (6 inches) thick, you’ll need to add material to provide a good bed for the new turf. Since you mention a lot of moss in your old lawn, it’s probably worth trying to improve the drainage too, as part of this process.
The ground needs to be dug over to a depth of 15-25cm (6-10 inches), the clods broken up and then, about a week or 10 days later, needs to be firmed up, either under foot or with a garden roller if the area is large enough to need one. Finally, a day or so before the turf is due to be laid, have a final check to make sure that everything is firm, level and that the top surface offers a good tilth to get the new lawn off to the best possible start.
Professional Advice
Good professional advice from someone with local knowledge and who has actually seen the site for themselves can often be the difference between success and failure when it comes to establishing a new lawn. If you haven’t already done so, it would be well worth making contact with someone reputable in your area who can give you some help – creating a lawn from turf can be a daunting prospect to undertake alone, particularly if the site does need a fair bit of preparation work to get it ready.
Best of luck with the new lawn.