Answer: It really depends on what type of tiller you are using.You might want to consider hiring someone with a lawn-tractor mounted hydraulic tiller for the first tilling. Tilling heavy clay can be quite a challenge with a walk-behind tiller, and can require a great deal of strength, especially on any type of hill. (I've been there!) Some people like to remove the sod before tilling. This will help decrease the number of weeds in the garden, but it also, unfortunately, removes a lot of topsoil and earthworms, especially on clay soil. I'd opt to till the grass in, if possible. One thing I've done in the past is cover the garden area with a sheet of black plastic or an opaque tarp for several weeks before tilling, to help kill the grass and also help the soil dry out by protecting it from spring rains.
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