Slugs and snails
Arion spp. / Helix spp.
Role in the garden
Nocturnal molluscs that gnaw young shoots, seedlings and tender leaves. Particularly devastating in spring in moist soil.
How to attract / manage it
Predators: ground beetles, hedgehogs, toads, frogs, slow-worms and birds (RHS); Indian runner ducks and flax or hemp mulch come from gardening practice.
Practical guide
Where to find them
Almost all plants, though some are less susceptible (tomato, for example). Favourite targets: lettuces, young plants, seedlings.
Prevention
Remove their hiding places (boards on the ground, stone piles). Sow susceptible plants such as lettuces on raised shelves out of reach. Keep the soil aerated, a dry mulch (flax, hemp) rather than a damp one.
Early signs
Seedlings shaved to ground level; older plants with irregular holes. The silvery slime trails on the ground and on the leaves leave no doubt as to the culprits.
Action / control
Gather them regularly at nightfall or early morning. Spread iron-phosphate granules (permitted in organic farming). Sink yogurt pots to the rim in the soil and half-fill them with beer (slugs are drawn in and drown). Another gentle trap: lay a board or a half raw potato on the ground in a cool, shady spot (or a melon or citrus peel, cut-side down); slugs shelter under it at night and are collected in the morning, a shelter-trap to empty daily (documented by the RHS; the potato variant is a gardening tradition). The nematode Phasmarhabditis hermaphrodita, a deadly parasite of the slug, protects susceptible crops such as lettuces, in moist soil between 5 and 20 °C; it rarely reaches snails (RHS).
Sources
- RHS (Royal Horticultural Society) : Slugs and snails (rhs.org.uk/biodiversity/slugs-and-snails)
- Règlement d'exécution (UE) 2021/1165 de la Commission, annexe I (phosphate ferrique, molluscicide autorisé en production biologique)
Favourite plants / resources
Related plant entries
Lettuce
A quick-harvest Asteraceae (45-90 days depending on variety), ideal as an intercrop between slow plants (cabbage, leek). Prefers partial shade in summer to avoid bolting. A notable accumulator of cadmium in polluted soil: to be avoided in urban growing on untested soil.
Cabbage
A brassica with a long rotation: 4 to 5 years between two brassicas, 8 to 10 years after a clubroot attack (Réussir Fruits & Légumes, 2022), whose spores (Plasmodiophora brassicae) can contaminate the soil for up to 20 years (RHS). Very greedy (nitrogen, calcium, water). To be planted after a legume to benefit from the nitrogen.
Brussels sprouts
A late long-season brassica: occupies the soil from April to February. An excellent autumn and winter transition plant, to be earthed up for stability. Pinching out the head ('topping') in late August encourages the sprouts to swell evenly. Frost converts starch into sugars: the sweetest harvest is after the first frosts.
Cauliflower
Very greedy for nutrients and water, to be placed after a legume green manure or on a bed well amended with mature compost. Fold the outer leaves over the white curd to protect it from yellowing (sunlight), that's the natural 'blanching'.