Slugs and snails in a greenhouse

Confirm the night visitor

Missing young seedlings, ragged holes in leaves and slime trails are classic clues, but look for the animal before blaming every hole on a slug. Check after dark with a torch or early in the morning, and lift pots, trays and loose boards. The RHS slugs-and-snails guide notes that feeding often occurs at night, leaving damage visible before the animal is found. Caterpillars and other pests can also chew leaves, so use several clues.

The smallest seedlings are the highest priority. A mature pepper may lose a little leaf area without consequence, while a tray of newly emerged salad plants can be erased overnight. Move vulnerable trays to a clean, stable bench where you can inspect underneath and around each pot. This improves access but is not a barrier: slugs can climb and hide in a tray that was already infested.

Remove hiding places and inspect arrivals

Clear fallen leaves, old cardboard, spare pots and wet debris from the floor and beneath staging. Keep paths and drainage in good condition; persistent puddles create shelter and a slip hazard. Check the bottoms of outdoor pots before bringing them into the greenhouse, including saucers and plant labels. A clean greenhouse is not slug-proof, but fewer hidden damp niches make early detection easier. The greenhouse hygiene guide includes this routine.

Collect slugs or snails found around valuable plants by hand if you are comfortable doing so, and follow local humane handling practice. Check repeatedly after damp evenings. A single night of collection is rarely an end to the problem because eggs and more visitors may remain. Use traps only if you will inspect and empty them; unattended wet traps can become new attractants or hazards in a narrow aisle.

Use biological controls selectively

The RHS describes a slug nematode, Phasmarhabditis hermaphrodita, that can be watered into suitable moist soil when the temperature meets supplier conditions. It affects slugs, including species that are not damaging your crops, and is much less likely to contact snails. It may be poorly suited to a paved greenhouse with plants solely in pots, or to cold or dry soil. Do not buy a nematode pack without a suitable application area, target and timing. The biological-controls guide explains this choice in context.

The RHS advises against slug pellets, including some marketed as organic, because of wildlife impacts. We do not recommend a pellet here. If considering any pesticide, check the current HSE amateur database and exact product label for crop, use situation and safety restrictions. A marketplace description is not authorisation.

Keep vulnerable crops growing

Sow a few extra seeds where losses have been recurring, but do not accept repeated damage as inevitable. Move trays, inspect incoming plants, water for crop need rather than leaving a wet floor, and look after dusk. If a plant fails without chewing or slime, reconsider damping off or root problems. The best response follows the evidence at the plant, not the first pest product in a search result.