Pricking out – advice for Greenhouse and Polytunnel users from horticulturalist Peter Whyte

When seeds have been sown and germinated in a seed tray, the process of separating the tiny plants and transplanting them into individual pots or containers is pricking out. It’s an essential skill for greenhouse users who raise plants from seed. Do it as soon as the seed-leaves on the new plants are opened out fully: delaying longer allows their roots to intertwine so that separating the plants damages them more severely. Fill compost loosely into the containers to be planted up. Level it but don’t firm it down. Using an old teaspoon, a metal tag or similar, dig under a seedling from the side as you lift it by one of its seed-leaves. Lower the roots down into a hole punched in the centre of the potting mixture in the target container and tap the container to level the compost around it. Firm it gently with your fingertips and water it. Set it somewhere warm, sheltered and out of direct sun until the plant recovers from the shock of transplanting and starts growing again.

Avoid sowing seed too thickly in seed-trays, as the seedlings end up too close together for easy pricking out   Do as little damage to roots as you can while pricking out so the plants will recover and grow faster. Always hold seedlings by one seed-leaf and never by their stems: stems are much easier to crush than leaves and a plant with one damaged leaf still has another.

If a seed-tray is too congested because of sowing thickly or delayed pricking out, all is not lost. You can still cut the solid block of root-bound compost into squares, pot up each square and reduce the plants in each to one by snipping out the rest.