A raised bed placed directly over the natural soil typically doesn’t need a whole lot of consideration for drainage. If you are building your raised bed over a solid surface, like concrete, or any other substrate that doesn’t drain well, you’ll want to take some extra steps to make sure excess water can flow out.
Both raised garden beds and planter boxes require good drainage for their plants. Technically these are just two different varieties of raised beds.
For planter boxes, the containers should to have holes drilled at the bottom. You will need to check to ensure that they drain water well.
In order to achieve good drainage, add one part of perlite and one part of peat moss to two parts of soil from your garden. Mix them thoroughly until they become even. The resulting mixture will be loose and light in weight with good drainage and aeration.