These gastropods (Snails and Slugs) are a fact of life in damp coastal BC. Two factors, however, can be used to minimize their impact on your organic vegetable garden. First, they shun sunlight, and are mostly active at night. Second, they require ample moisture to thrive and breed.
The organic gardener’s best control is to minimize the amount of water in the garden: Remove all unnecessary objects under which moisture can collect – all pots, bricks, boards, hoses, and tools should be removed from the garden. Water only in the morning, and take advantage of evaporation and drainage during the day. By the evening, beds should be relatively dry. Watering in the evening, or at night, is a recipe to cultivate a strong population of slugs & snails.
Snails withdraw into the moist shelter of their shells during the day, so they are easily hand-picked from the growing area, and tossed out of harm’s way. Slugs retreat into cracks and crevices, and under objects during the heat of the day – so use this behaviour to trap them. Early in the evening, lay down a piece of plywood (or several pieces) near your growing area. The next morning, lift the plywood, and remove all the slugs that have gathered under it.
If the vegetables in your garden are packed in very close to one another, you can end up creating a damp canopy under which slugs and snails (and woodlice) can flourish. So space your plants with this in mind – a few more inches here and there can make all the difference. Remove the large outer leaves from your lettuces and Brassicas. This will increase air flow and help to dry the soil up at least somewhat.
Slugs and snails both play a role in your garden’s ecosystem. Love them or hate them, they are part of a food chain. So we need to work around them. Gardeners frequently recommend laying down one material or another to create a barrier around your plants. Everything from eggshells to coffee grounds, pennies to human hair. The truth is that when it’s damp enough, slugs and snails can glide along without noticing your efforts. Controlling moisture is a safer, more ecologically sound approach.*
*Update May 24, 2017: Customer Catherine sent in a photo of her dahlias that have recovered from being eaten to the ground level after she installed the Slug Shield. This is just copper mesh that forms a collar around each of her dahlias. This is a bit fussy to install, but perhaps worth it on specimen plants that warrant special protection.