There are a few different options that you can use for drainage in the bottom of a raised planter. One is to simply use rocks or gravel. This will help to keep the water from pooling at the bottom of the planter and will allow it to drain away quickly. Another option is to use a layer of fabric, such as burlap, beneath the soil. This will also help to keep the soil from becoming too saturated with water and will allow for better drainage. Finally, you can also add a small hole in the bottom of the planter for drainage. This is probably the simplest and most effective option, but it does require a bit more effort to set up. Whichever option you choose, make sure that you have good drainage in the bottom of your raised planter so that your plants can stay healthy and thrive.