Snails lover your dahlias! They be protected by laying a barrier around with coffee remnant, crushed egg shells or shells.
Garlic is poisonous for snails; They will avoid your plants if you spray them with garlic extract. You can do this yourself. Cut a garlic bulb into pieces, pour 1 liter of hot water and let it soak for a day. Remove the garlic, pour the extract into a sprayer and spray. Spray again after rain fall.