Action plan: Nigel Colborn’s essential jobs for your garden this week 

FRESHEN UP YOUR POND 

Ponds can often become tired and grubby in August. In hot weather, blooms of blanket weed or other algae can happen rapidly, especially if the pond is over-populated with fish. Those excrete nitrogen, which increases algae levels.

For water purity and a healthy pond, much of the surface should be shaded by floating leaves of water lilies or other aquatics.

A cover of 70 per cent or more is desirable at the height of summer. That keeps the water cooler and reduces light intensity, slowing the growth of green algae and invasive water weed.

To remain healthy and clear, ponds also need plenty of submerged, oxygenating weed. But if it becomes too dense, haul some out.

Check hanks of removed weed for trapped wildlife. Fresh water shrimps, water beetles or dragonfly larvae should be returned to the water.

Dragonfly nymphs and water beetle larvae bite so handle those with caution.

Blanket weed and algae will reduce naturally when day length shortens more rapidly.

Using chemical algicides provides temporary relief, but not a permanent cure. 

SUMMER PRUNING 

Apples, pears and other fruits grown as espaliers, cordons or fan-trained, will benefit from August pruning, to boost future yields and ensure good quality fruit. Pruning now will also help keep the trees in the desired formal shape. With trained trees, select young shoots which have grown from buds on the main branches. Cut each just above the third or fourth leaf from where it joins the mature stem. The shortened stumps will then develop fruiting spurs for next year’s crops.

BEAT BLACKFLY 

Try non-pesticide solutions. Rub out aphid colonies by running your fingers and thumb along infested stems. Make it less unpleasant by using disposable gloves. Hose away blackfly colonies. If using insecticide, fatty acid or plant oil-based contact sprays are kinder on non-target insects.

QUESTION 

My neighbour has a unique nasturtium with deep crimson flowers and dark leaves. Can you grow young nasturtiums from cuttings? I have a conservatory.

Mrs J. Lawrence, Surrey. 

Yes. In September, select and remove a few healthy shoots, up to 8cm long. Strip the lowest leaves and stick several cuttings into a 9cm plant pot with a 60-40 mix of potting compost and grit or sand.

Cuttings root rapidly in propagators , or keep pots well-lit, warm and in good light. Keep compost moist and transfer into individual pots.

PLANT OF THE WEEK: HIBISCUS SYRIACUS ‘LAVENDER CHIFFON’

August-flowering shrubs are to be treasured. Compared to the spring bonanza, shrubs are scarcer now. But hardy Hibiscus syriacus is an outstanding exception. Growing to 2m, the shrubs carry masses of saucershaped or double flowers from now into early autumn.

Colours run from pink through mauve to blue or white.

Hibiscus ‘Lavender Chiffon’ has flowers in lilac pink with dark red veining towards the petal bases. Despite being double, they have pollenbearing stamens, so benefit bees and other insects. These shrubs thrive in full sun or sparse shade in freedraining soil.