- If you have brassica plants, such as brussels sprouts and cabbages, growing on the vegetable plot, now is the time to be extra vigilant and prevent them from being ruined by cabbage white butterflies. The hairy, yellow and black grubs of this common pest emerge in the early summer and feed on the leaves, often doing serious damage. To avoid problems, examine the plants on a daily basis, especially the undersides of the leaves, and remove any grubs that are found. If you notice clusters of small yellow eggs on the leaves, these should also be rubbed off and destroyed.

- If you live next to mature ash and sycamore trees, check ornamental borders for self-sown seedlings from these trees and remove them. If left, the young trees will grow rapidly, putting down deep and penetrating roots that use up valuable moisture and nutrients.

In extreme circumstances, the roots of these trees can damage underground drains and wall foundations.

- On hot days, open the greenhouse door and roof vents (preferably first thing in the morning) and damp down the floor using a watering can. This will stop the temperature inside from soaring to levels that can damage plants. It will also increase the natural humidity in the air, reducing the risk of pests such as red spider mites.

- To keep peonies in top condition, dead-head the spent flowers as soon as they fade. Leaves and stems should be allowed to die back naturally.

Readers’ questions

The leaves of my pear tree are pale and puckered. What is wrong? - P Francis, Worcester

In mid- to late spring, the young leaves of pear trees are sometimes covered in small pink or yellow blisters that turn brown and black in summer. This damage is due to pear-leaf blister mites, which feed on the leaves. It is almost impossible to eradicate these tiny creatures: the only solution is to remove the affected leaves, if possible and practical. In most cases, however, the damage is only disfiguring, and the crop of fruits will not be adversely affected.=

gardenexpert@sunday-times.co.uk

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