What Is Eating My Brassica Seedlings at Night?

Young broccoli or cauliflower transplants that look healthy in the evening but are damaged or entirely consumed by morning have almost certainly been attacked by slugs. Slugs are nocturnal feeders and are particularly destructive on young, soft-tissued brassica transplants in the first two weeks after planting. A single slug can consume an entire small seedling in one night, and a population of slugs can eliminate a newly planted bed within days.

Confirming slugs as the culprit

Slug damage leaves ragged, irregular holes or completely severed stems, with silvery slime trails on the soil surface or remaining leaf fragments. Go out with a torch on a damp evening and you will find the slugs feeding. They prefer mild, wet conditions and are most active in spring and after rain. Caterpillar damage also produces ragged holes but occurs during the day and is not accompanied by slime trails.

Slug pellets

Ferric phosphate slug pellets (widely available, wildlife-safe and certified for organic use) are the most reliable control for protecting transplants. Scatter them sparingly around the planting area immediately after transplanting and after rain. They are significantly safer than metaldehyde pellets and do not harm hedgehogs, birds or other wildlife. Reapply every one to two weeks during wet weather.

Barriers and traps

Copper tape around raised beds creates a mild electrical deterrent. Crushed eggshells, grit or sharp sand around individual plants provides a physical deterrent, though it needs regular replacement after rain. Beer traps (any container sunk to soil level and half-filled with beer) catch large numbers of slugs overnight and are effective in a small area.

Once past the vulnerable stage

Established brassica plants — those with more than six true leaves and a thick stem — are rarely severely damaged by slugs. The feeding focus is almost always on tender young growth. Protecting the first three to four weeks after transplanting is the critical window; after that, slug damage is cosmetic rather than plant-threatening.