How to propagate large bitter-cress in the UK

Late winter to late spring, under cover for anything tender. British light levels before February are the limiting factor rather than temperature — seedlings started too early stretch and weaken. Sowing dates copied from US packets run several weeks early for Britain, and the limit is light rather than warmth — seedlings started in January stretch towards a window that has nothing to give them.

Peat-free seed compost. Peat-free is the British default now, and most retailers stock it as standard. The mix matters more than the brand — free drainage is what protects new roots through a damp British autumn.

A heated propagator brings tender sowings forward by several weeks in an unheated British house.

Germination varies by species; most warm-season crops need 18-24°C to start.

Most propagation guides online are written for warmer, brighter conditions where a windowsill will root a cutting on its own. British gardening organises the year differently — softwood in spring, semi-ripe in late summer, hardwood over winter — and the RHS specifies bottom heat of 18-24°C (64-75°F) for softwood cuttings, which an average unheated British room does not reach. British winter light is the other constraint: the same cutting that roots in three weeks in June can sit for three months from a November windowsill.

The technique is usually the same — seed (with cuttings or suckering as a shortcut where possible). What changes here is when you do it, what you root it in, and whether you need heat. Our large bitter-cress propagation guide covers the general method; this page covers the British calendar and conditions.