Why Are Slugs Destroying My Bean Seedlings?

Bean seedlings — particularly in the two to three weeks after germination or transplanting — are among the most slug-vulnerable plants in the garden. The large, succulent, relatively soft cotyledons (seed leaves) and the thick, moisture-rich stems of young beans are highly attractive to slugs, which can consume an entire seedling down to a bare stump overnight. The damage is worst in warm, wet conditions — the same conditions in which beans are typically transplanted in late May and June — and in gardens with high slug populations from dense mulching or nearby long grass.

The two-week vulnerability window

Bean seedlings are most vulnerable in the first two to three weeks after emergence or transplanting. Before this point they are tiny and easily completely consumed; after this point the stems begin to lignify (toughen and woodify) and slugs find them much less palatable. The goal is to protect the plants through this critical window. Once beans have a stem 30–40 cm tall and are growing vigorously, slug damage is still possible but is rarely crop-threatening — occasional bite marks on leaves are cosmetic rather than damaging.

Effective slug control methods

Iron phosphate slug pellets (widely available, safe for hedgehogs, birds, and pets) placed around and between the seedlings at the recommended rate are highly effective when used consistently. Refresh pellets after heavy rain. Nematode biological control (Phasmarhabditis hermaphroditis — water-in granules available online) works well applied to the soil around transplants, with the protection lasting six weeks. Beer traps catch significant numbers near the plants. Hand-picking after dark on warm, damp evenings is surprisingly effective and free.

Resowing or replacing

If a row has been wiped out by slugs, it is almost always faster to resow or transplant replacements than to wait for survivors to regrow. Start fresh seed under cover in pots, allow to reach 15 cm, harden off, and replant with slug protection in place from the moment of transplanting. Beans grow so quickly that a replacement sowing made two weeks after the original planting date can catch up to the original schedule within four weeks.