Here are your gardening jobs for the month – with added links if I have more information on the subject. They are all still relevant to do now if you’ve fallen behind or if the weather’s been bad.
Take cuttings of patio and container plants ready for next year.
Prop up tall perennials such as lupins, delphiniums, and gladioli if staking was neglected earlier in the season.
Liquid feed container plants and keep well watered in dry spells.
Watch out for aphids (greenfly and blackfly) on stems and leaves of young shoots.
Small holes and tears in the new foliage of ornamentals such as Caryopteris, Fuchsia and Dahlia are most likely caused by capsid bug damage.
Powdery mildew can play havoc with plants such as clematis, roses, and honeysuckle.
Look out for tall, flowering stalks on established bamboo and remove them promptly. Flowering can weaken the plants, as well as being unsightly.
Ensure newly planted trees and shrubs do not dry out. They need much more water than people imagine.
Yellow and distorted leaves on cherry laurel (Prunus laurocerasus) show a powdery mildew problem.
You may notice damage to leaves of Viburnum by viburnum beetles. The damage is not usually bad enough to call for treatment.
Top up ponds and water features if necessary – a spray attachment on the hose will aerate the water. Any pumps on water features should be left on during sultry nights, as oxygen levels are lower in such conditions.
Remove dead foliage and blooms from water lilies and other aquatic plants. Cut back any marginal plants that are getting out of hand. Continue to skim blanket and floating weeds.
Some seeds are best planted just after collection, and others may need specific climatic conditions to break dormancy (e.g. some alpines). If unsure, then sow seeds in ‘batches’, i.e. one immediately after collecting, one in winter, and one in the following spring.
Mulching borders can help retain moisture, and keep down the weeds – this will save a lot of work. A really thick layer of mulch (5-7.5cm/2-3in all over) works best.
Look out for and treat black spot on roses and scab on Pyracantha.
Fast-growing hedges such as Leyland cypress should be clipped as necessary throughout the growing season, but avoid birds’ nests.
Neat circular areas removed from the edges of rose and other leaves are telltale signs of leaf-cutter bees at work. These fascinating creatures are best tolerated since damage is rarely severe.
Cut back delphiniums and geraniums after the first flush of flowers to encourage a second flowering period. Feed after cutting them back.
Divide clumps of bearded iris.
Pinks and carnations that have become leggy, can be propagated by layering or by cuttings. Propagation can improve the look of untidy clumps.
Most perennial weeds are best dealt with in the summer when the weeds are in active growth. Digging out often works, but applying a weedkiller can be more practical, particularly for large areas.
The sudden collapse of apparently healthy clematis, especially the large-flowered cultivars, could indicate clematis wilt.
Prune (supposedly) June-flowering shrubs such as Philadelphus and Weigela after flowering. Prune deciduous magnolias if necessary.
Tie-in climbing roses and ramblers as they grow. Remove rose suckers and tree suckers.
Thickened and curled margins on bay trees (Laurus nobilis) are a sign of damage by the bay sucker. Scale insects can also affect bay at this time of year.
Many conservatory and greenhouse pests will be active during the summer months. Check plants regularly for signs of glasshouse whitefly, leafhopper, glasshouse red spider mite, mealybugs and scale insects. Yellow card sticky traps are a valuable, low-cost tool for monitoring numbers and types of flying pests in the greenhouse. If large numbers of a particular pest are found, treatment can be instigated.
Cover ponds with nets or safety grilles in gardens where young children play. These have the extra advantage of preventing leaves falling into the pond. Clean out debris lurking in the depths of the pond. This will improve the water quality and prevent excess debris from promoting the growth of weeds, algae or marginal plantings, and from releasing toxins that could harm fish or wildlife.
Cutting back plants in baskets followed by feeding can encourage new growth and help revive tired displays.
Plants with a carpet-like growth habit, e.g. some alpines, can become patchy, with central areas dying off. These patches can be in-filled with gritty compost, to encourage re-growth.
Some late-flowering border perennials may benefit from a quick-acting feed before they come into bloom, especially if the soil is not very fertile.
Start collecting seed from plants you want to grow next year, especially hardy annuals such as Calendula, poppy, and love-in-a-mist.
Take semi-ripe cuttings of shrubs such as Choisya, Hydrangea, and Philadelphus. Root them in pots of gritty compost in a cold frame or even with a plastic bag tied over them.
Clematis can be propagated by taking internodal cuttings (i.e. taking stem sections above and below a leaf, and not cutting the stem immediately below a leaf joint).
Brown patches on conifers may show an earlier infestation by the cypress aphids. Telltale signs include black sooty mould along the stems and shed skin cases. Spraying earlier in the summer may have helped, but once the damage is done, conifers can take a long time to recover. Where hedges are affected prune out brown shoots and tie in neighbouring branches to help fill the gaps.
Cuttings can be taken and grown on in the greenhouse. fuchsias and Pelargoniums are good candidates.