Top soil on top of grass

[joeandrews]

I have built myself a raised bed out of sleepers.

I've built it on top of the lawn, can I just chuck a load of top soil in there now and get planting, or do I need to remove the grass first or something like that?

Also, why do some people line the inside of the sleepers with landscaping fabric?

Thanks.

 

[Space cat]

It probably depends on how deep the soil will be. I know for a fact that if you spread a thin layer of soil over a lawn, the grass will come up through it. I've used this trick many times to level out hollows in our lawn. What would happen if I put down several inches of soil? I don't know.

One thing I have been told by more than one gardener is that old turf is the best compost you can get and so, if I was going to grow stuff in soil on top of a lawn, I would dig up the turf and flip it upside down first.

 

[roberta1000]

I have a large raised bed with a brick surround over what used to be a grass area. The depth of topsoil varies from around 18" down to around 8". I didn't dig over or kill off the grass first and none ever came through. I'd suggest that you decide what depth of planting you're likely to want and if that takes you below the existing level of grass then maybe dig it over otherwise not bother unless you fancy the exercise. After all if the grass doesn't come through then it will rot away whether you dig it over or not.
As an afterthought if it is rock hard then maybe breaking it up would help with future growing but otherwise it hasn't been a problem to me.
I think the only value of the landscaping fabric would be to help prevent soil seeping through the irregularities if you need things to be nice and tidy. It's permeable so wouldn't make a pond. Mine's brick so not much comes through.

 

[r896neo]

its not the grass you need to deal with but the fact that most areas of lawn are heavily compacted which makes drainage poor, best bet is to fork the area well to break it up and improve drainge from your bed.

 

[Srodders]

The fabric is to stop the chemicals from the preservatives used on the sleepers lecching into the soil. This is for veg. growing so if you are only ever growing ornamentals in the bed there is no need. No real need to dig over the grass either unless you plan on growing root veg in there.