This method allows you to retain the original organic matter by using a power tool to turn the sod under. It also allows you to easily incorporate compost or soil amendments into your bed without a lot of digging. Although tilling enables you to plant your garden quickly without a lot of labor, it often propagates grass and other weed seeds.
Breaking up sod with a tiller requires a strong back, but not as much muscle as digging does. You can use this method as soon as the soil is dry enough to be worked.
To get started, rent a heavy-duty rototiller from a farm or hardware store. Fork compost and any other soil amendments onto the sod before tilling. The tiller will work them into the soil. Well-established sod might require more than one pass with the tiller. Allow the overturned sod to break down for a week or two before planting.
Your new bed can be planted soon after tilling, but grass might grow back up through the overturned soil. Tilling also brings weed seeds to the surface that can germinate later and cause big problems in your garden. If you delay planting by a month or two, you can dispatch grass and other weeds as they emerge.
Pros: Retains organic matter; is quicker and easier than digging; permits almost immediate planting.
Cons: Renting a tiller can be expensive; tillers don’t work well on rocky sites, wet soil, or clay-rich soil; grass can grow back if you plant soon after tilling; tilling propagates weeds and disrupts soil structure.
(Image courtesy of halle via a Creative Commons license.)