The main strawberry season is starting. For best results, pick fruits with a short stalk attached. This prevents disease and means you can keep them in the fridge for up to 48 hours. If any show signs of mould — usually in warm, damp weather — remove them straightaway or they may infect the healthy fruit.

If you have some established asparagus plants, stop harvesting the spears about now. Leave any further spears to develop into tall, fern-like growth, which helps the plants to build up food reserves for next year’s crop. Keep the area weed-free and water the plants in dry spells.

To keep Deutzia gracilis vigorous and healthy, lightly prune the spent stems once the flowering display has ended. Cut as far as obvious shoots further down the stem. On mature specimens, older growth should be removed to ground level.

Readers’ questions

The leaves of my water lily are covered in greenfly. What should I do?

L Rouse, by e-mail

In the summer, colonies of small, dark-green and brown water-lily aphids can be a real nuisance, as they suck the sap from the floating leaves (and infest the flower buds), causing discoloration and plant distortion. The best control measure is to use jets of water from a hosepipe to knock the aphids carefully off the leaves and into the water; they will then be eaten by fish and other predators.

When should I sow winter radishes?

N Langley, Gillingham

Winter radishes, such as ‘Black Spanish Long’ and ‘China Rose’, produce large roots that usually have a stronger flavour than summer radishes. Choose a sheltered, sunny spot with fertile, well-drained soil. Sow the seeds in ½in deep drills in July or August (order now: try www.chilternseeds. co.uk). When seedlings appear, thin them to 6in apart, keep the ground moist and harvest (as required) from late October onwards. If poor winter weather is forecast, surround the plants with a protective layer of straw.

gardenexpert@sunday-times.co.uk

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