Do I need to kill the grass or till the soil before starting a raised bed?

Question: 

Do I need to kill the grass or till the soil before starting a raised bed?

Answer: 

Before filling raised beds, remove the grass sod, if possible, and work up the existing soil with a rototiller or spade.  Add a few inches of the soil mix, then incorporate it into the existing soil.  Continue to add and incorporate additional soil mix until the raised bed is filled.  Incorporating the soil mix into the existing soil prevents the formation of distinct layers in the raised beds.  Distinct layers of soil impede water movement and discourage root growth. 

If contamination is a concern, place a layer of woven geotextile fabric between the native soil after stripping sod and build the raised bed on top of this. The woven fabric will slow, but still allow water movement into the soil below, but will reduce root growth through the fabric, preventing nutrient (or contaminate) uptake from the native soil. Do not use non-woven fabrics (e.g. pond liner) since these will not allow drainage. If drainage into the native soil is too slow, holes or weeps may be added to the sides of the raised bed to allow for additional drainage.

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