I have created a pond on my terrace using a water tank. Which water lilies can I plant inside?

G Marston, by e-mail

The best lilies to use in container ponds are miniature varieties, as they have a maximum spread of just 2ft. Try Nymphaea ‘Pygmaea Helvola’ for its small, star-shaped, soft-yellow midsummer flowers and curious blotched leaves; Nymphaea ‘Pygmaea Alba’, which has white and golden-centred flowers; or Nymphaea ‘Pygmaea Rubra’, which has deep-pink flowers. All should be planted so that they are covered by 6in-9in of water; late spring is an ideal time to do it. Waterside Nursery (01455 273730, www.watersidenursery. co.uk) has a selection of miniature water lilies.

How can I prevent red spider mites infesting my unheated greenhouse?

T Emerson, Wolverhampton

Contrarily, these tiny sap-sucking pests are yellow-green rather than red. They attack plants such as cucumbers, aubergines and fuchsias. In unheated greenhouses, they are most active between late spring and autumn; signs of infestation include a mottling, yellowing and withering of leaves, and a mass of fine webbing, especially on upper growth. The mites are hard to see, but can be found on leaf undersides. They thrive in hot, dry conditions, so keeping the greenhouse well ventilated, misting the plants and damping down the floor regularly will help to keep them at bay. A predatory mite (available from www.just-green.com) can also be used to control them. These are most effective in temperatures of more than 16C.

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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