When to plant Zinnias in London

Sow seeds in modules around 28th March - 11th April, about 1 cm deep in fine compost. Keep them warm and bright, and water lightly so the compost stays just moist.

Pot seedlings on around 11th April - 2nd May, as soon as they have their first pair of true leaves. Move them into individual small pots so the roots do not become cramped, and keep them warm in good light without overwatering.

Harden plants off over 15 days before planting out, from 25th April to 9th May. Put them outside during the day at first, then bring them in at night until they cope with cooler air and brighter sun.

Plant out around 9th May - 23rd May into fertile, free-draining soil in a warm, sunny, sheltered position, spacing plants 30 cm apart. Water in thoroughly straight away, and protect young plants from slugs.

From 9th May to 10th November, water at soil level during dry spells and avoid wetting the leaves, as damp foliage encourages fungal disease. Once flowering begins, feed plants in containers with a high-potash liquid feed according to the label.

Around 23rd May - 20th June, pinch out the main growing tip above a pair of leaves when plants are 20–30 cm tall to encourage branching. Support tall cultivars with canes or netting before the stems become top-heavy.

Every 14 days from 20th June to 10th November, cut flowers for the house or remove fading blooms back to a leaf joint. Regular cutting and deadheading encourage the plants to keep producing flowers until frost.