You really need to know what it is and the only way to know for sure what it is, is to go out at night and find the culprit. Having said this, you can use the nuclear method and treat for everything that it could possibly be. It could be slugs/snails, pillbugs and you would use Sluggo Plus for these critters. It could be caterpillars and you would use a Bt (Bacillus thuringensis) product on them. It could be some type of insect and you would use a spinosad product like Captain Jacks Dead Bug on these. Or it could be a 4 legged varmint like a rabbit and you would use a 12 guage or a .22 on them.