Should I remove the grass before building a raised garden on top?

It actually depends on what type of grass you have and how deep your bed is going to be. If it is an aggressive creeping type of grass like bermuda, you should probably hose it down with roundup before you put the bed in. If it's something like rye or bluegrass you're probably fine.

If your bed is going to be really deep, like 18 inches or more, you probably don't have to worry about anything coming up through that. Even the creeping stuff will only go through 6 or 8 inches.

You need to remove the grass because regardless if you put dirt over top of the grass the grass will grow up into your raised garden. You can dig the grass up and place it some place else. If you don't want to pull it up then you need to lay something down between the grass and the dirt so that the grass can't grow up into your garden. Without doing the removal or laying something in between you will be pulling grass out of your garden daily.

This will take some work but, it will pay off in the long run.

Find a weed and grass killer and spray it on the area you

are going to put your raised bed.

Till the area after the grass has died, and rake the area clean

of the roots, making sure you get as much as possible.

Level the area, put black thick plastic down and then you

can put your form up.

Fill the raised bed with potting soil (3in from top) and you will

be on your way.

You will have to water at least once a week, when you do this,

allow the water to run out the bottom of the bed and you will

know you have watered it enough.

You will have to add several bags of potting soil every year.

If you can find "cotton seed hulls" before you plant next year:

add a bag per bed, till in and water generously.

Remove the grass or put that garden cloth down first or it will send shoots up through your garden.

Lucy is right