"It sure would save my back if I didn't have to take out the existing grass..."
This is one of those questions we get asked a fair bit, and we understand why. You want to be outside enjoying your yard, not hard at work.
Unfortunately, the answer exactly the one you were probably hoping it wouldn’t be: you do need to take out the old turf before you put in new sod.
One of the main reasons is, if you put new sod on top of old vegetation, the new sod’s root system will never actually make contact with the soil on the other side of the old turf, and it will die.
When people hear this, their next question is whether they can put a layer of soil on top of the old turf, and then put on the new sod. What happens in this scenario is that the old vegetation will break down (decompose), and this process releases gasses that will kill your new sod.
Also, by having that layer of vegetation under the soil, the roots still can’t get through, and you will be creating drainage issues.
The best thing you can do to prepare for new sod is to completely remove the old turf, mix some Black Garden Soil in with your existing soil (we recommend BigYellowBag Black Garden Soil), and then lay the new sod.
Don’t forget to thoroughly water your new sod within half an hour of it being laid, and frequently for the next two weeks.
A little bit of extra work at the start of the project will ensure that you get to sit back and enjoy having a lawn that’s the envy of the neighbourhood for a long time to come.