Yes, you'll need drainage holes in these planters. There are two ways you can do this. Each has its merits and both require some finicky work. Firstly, you can follow the method mentioned above with drilling holes into the bottom of your planter. Secondly, you an add PVC pipe for drainage, which is what I did in the colorful planters above. The PVC pipe requires measuring it and cutting it to the right height to go from the inside planter to the outside one. Oil it well and pour the concrete around it. With the PVC pipe, you will inevitably be chipping at it (or drilling it!) to get the excess concrete out of the hole, so choose your method based on what you have on hand.