Answers to Your Questions: How Do I Replace an Old Lawn?

Question

Can sod be installed over existing old lawn after most weeds have been destroyed? Will the sod be allowed to die to make compost for the new sod?

Answer

Yes, you can cover a lawn in poor condition with sod and effectively, without light, the old grass will die and decompose, feeding the new grass. But before doing so, I suggest you have a soil analysis done to try and find out why the previous lawn had so many weeds. In all likelihood, the soil was of poor quality and probably too acidic too, which prevented the grass from benefiting, giving weeds a chance. And why invest in a new lawn when the soil would be unable to support it? If the old soil is found to be too acidic, which it probably will be, apply lime as recommended in the report before going any further.

Also, don’t lay the new lawn directly on top of the old one: you need a layer of good soil between the two. How thick should the soil be? If the results of the soil analysis indicate that the soil was of good quality, 4 or 5 cm (2 inches) of lawn soil will suffice. Otherwise, apply at least 20 cm (8 inches). If this is too much of a build-up for your taste (20 cm of soil will give your lawn a much-needed boost!), it’s best to remove the old turf before adding the new layer of soil. You can hire a turf cutter to do the job effortlessly.

Seed or Sod?

Finally, consider sowing mixed grass seeds rather than laying sod: it costs less and generally gives better results in the medium term, not least because you can then choose a seed mix suited to your conditions, whereas sod is best suited to perfectly sunny sites with very rich soil. The downside of seed is that it takes longer to establish… but what’s 2 or 3 weeks more on a lawn that’s expected to last 40 years or more? On a steep slope, on the other hand, sod is easier to lay.

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Larry Hodgson published thousands of articles and 65 books over the course of his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on August 12, 2006.