How can I stop my marrows from getting powdery mildew without using chemicals?

G Elliott, Liverpool

Marrows are susceptible to a fungal disease called powdery mildew, which attacks the plants during warm, dry weather. The first signs of trouble are powdery white patches on the leaves and stems. These can spread to cover the leaves; a badly affected plant may become distorted or even die. Fortunately, there are ways to reduce the chances of mildew, such as growing your marrows at the correct spacing to prevent overcrowding, and removing all weeds. It is also important that the soil around the roots does not dry out, so mix plenty of compost into the planting holes and spread a mulch over the ground to help retain moisture. This fungus can overwinter on plant debris, so always clear up the old stems and leaves in the autumn.

Should I deadhead the fading flowers of my peony?

H Warren, Torbay

Paeonia officinalis (common peony) is a clump-forming herbaceous perennial grown for its beautiful red, white or pink flowers in late spring and early summer and deeply cut, mid-green leaves. This cottage-garden plant is ideal for a sunny or partially shaded spot and a fairly moist but welldrained soil. Once established, it will reach a height and spread of about 3ft. To keep the peony vigorous, the spent flower heads should be removed as soon as they fade – trim them off with secateurs. The leaves are highly ornamental and are best left to die back naturally before cutting them down to ground level in the autumn.

Neil Wormald is a qualified horticulturalist. Send your questions to Garden Expert, Home, The Sunday Times, 1 Pennington Street, London E98 1ST, or e-mail: garden.expert@sunday-times.co.uk

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