Snails and slugs can cause problems in container gardens and cause lots of damage to to young and tender plants, once they found access to the plants. Snails and slugs are quite lazy and opportunistic and usually don't move to far away from their favorite food plants to find shelter during the heat of the day only to return during the following night to continue feasting on the leafy plants and vegetables.
If they are not removed they can destroy all the plants in the space of just a few days. so it is advisable to regularly inspect the state of the young plants and keep an open eye for any clearly damaged leaves. Once you found partially eaten plants on any given morning it is best to begin immediately with preventative actions to get rid of those hungry pests.
1. you should carefully remove all the plants from their current positions and look and check at their bottoms and sides for hiding snails and slugs. They love to hide on smooth surfaces like plastic sheeting and bags in shady and moist areas away from the burning sunlight. Check all the plants close the the damaged plants and the immediate surroundings for snails and slugs. A good time for this are early mornings especially if there are moist conditions outside which is by far the favorite climate conditions of snails and slugs. Take a bucket with lid and collect all the snails and slugs you can find in the surroundings of your container garden. Check under stones, rocks, under lids of pots and underneath plant pots as well. When you have stored your plant containers in old corrugated cardboard boxes you might as well find some earthworms and even earthworm cocoons which are of course beneficial for your plants. They love the cardboard and if it is shaded and moist will migrate back and forth between the cardboard and the soil of the plants
2. Once you have removed all the snails and slugs from the plant containers and their surroundings place the containers back in their place and get rid of the snails. You can collect the worms that you found as well and add them to your worm bin or compost heap or just leave them in the bottom of the cardboard box that hosts your plants if the conditions are allowing it
3. As an additional protection for your garden against snails and slugs set up some beer traps near your plants. Just fill small margarine tubs or similar plastic containers with beer and place them in the vicinity of your endangered plants. Snails and slugs are highly attracted by beer and if there are any left they will usually crawl during the night to the beer for a drink and will fall into the trap drowning in beer.
I hope this will help you protecting your precious food crops.