Gardening Methods

i want to do my garden with gravel and slabs …

so do i have to put anything like builders sand down before i lay the slabs or can they be plonked straight on the dirt ?

also do i have to get the plastic sheeting for between the mud and the gravel or will it be ok to just put down on the dirt ?

i am on a tight budget so looking for ways to save money
ok thanks guys, i well clearly just didnt have clue just moved into my first home and dont have a clue about any garden stuff…. and well a walkway then …