There are two common predators that work at night and leave holes: earwigs and slugs. Test for earwigs by taking a dampened roll of newspaper or similar paper and leaving it on the ground next to the plant overnight. In the morninng, place the roll (unopened) in a plastic bag and shake it. If earwigs  are present, they will appear and you can seal the bag and trash it. Several nights of this should eliminate the problem. If it is slugs, you might search for slime trails, actual slug presence. To keep slugs from entering the planters, place a sheet of copper under the planter so that all approaches are covered. You can also place copper tape around the edge of the planter. Slugs and snails will not cross copper surfaces. You can also use products such as Deadline, which is a liquid barrier to slugs and snails entering the planter. I hope  you defeat the critters that are causing the damage.