Essential gardening jobs
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Prune Wisteria back to a strong frame, including long summer growth.
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Don’t delay summer pruning fruits trained as restricted forms. Remove whip growth and tie in growth you are training to shape and encourage fruiting spurs.
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Deadhead flowering plants regularly, especially annuals to maintain flowers
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Watering! - particularly containers, and new plants, preferably with greywater, or stored rainwater.
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Harvest sweetcorn, courgettes and other vegetables as they become ready to encourage fresh fruiting.
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Continue cutting out old fruit canes on raspberries to promote bottom growth.
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Lift and pot up rooted strawberry runners to increase stock. These can be planted to replace older plants which have reduced fruiting.
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Keep ponds and water features topped up.
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Feed the soil with green manures – Galega officinalis is a good nitrogen fixing option.
Cutting back, pruning and dividing
Cut back the foliage and stems of herbaceous plants that have already died back (such as Dicentra, Papaver and anything outreaching its space.
Don't neglect hanging baskets – deadheading, watering and feeding will help them last through until autumn.
Deadhead plants such as Dahlia, roses, Penstemon and bedding plants to prolong the display of colour well into early autumn.
Don't cut off the flowerheads of ornamental grasses – these will provide winter interest.
Hardy geraniums can be cut back a little to remove tired leaves and encourage a new flush of growth.
Prune climbing and rambling roses that do not repeat flower, or produce attractive hips, once the flowers have finished.
Propagation
Pinks and carnations can be propagated by layering. Propagate irises by dividing the rhizomes if you didn’t do this last month.
Take cuttings of tender perennials such as Pelargonium and Osteospermum as soon as possible. A greenhouse, cool conservatory, or a light windowsill are ideal to house them until they are established.
Rock garden plants, such as Helianthemum, Aubrieta and Dianthus, can be propagated from cuttings at this time of year.
General maintenance
Feed containers, and even tired border perennials, with a liquid tomato food each week to encourage them to bloom into the early autumn.
Keep picking flowers from the cutting garden to encourage more flower buds to form and open.
Alpines that have developed bare patches of die-back, or have become weedy, can be tidied up by in-filling the patches with gritty compost. This will encourage new growth, as well as improve their appearance.
Most perennial weeds are best dealt with when in active growth, if necessary applying a weedkiller.
Trees and Shrubs
General maintenance
Continue to deadhead shrubs, such as roses, to extend flowering into early autumn. Spindly specimens that have lost leaves can be cut back a little further when deadheading to encourage new growth.
Thoroughly soak drought-stressed plants and shrubs, especially newly planted ones. Use grey, recycled or stored rainwater wherever possible.
Keep early flowering shrubs such as Camellia and Rhododendron well-watered during dry periods to ensure good flower bud initiation.
Propagation
Semi-ripe cuttings can still be taken to propagate many common garden shrubs (e.g. box, Ceanothus, lavender).
Rhododendrons, azaleas and Clematis can be propagated by layering.
Pest and disease watch
Brown patches, needle loss and sooty mould on spruce (Picea) trees are evidence of green spruce aphid damage earlier in the year.
Mid to late August is a good time of the year to apply biological controls for vine weevil. Grubs will be starting to hatch and soil temperatures are now suitable for the nematodes to be effective. Target vulnerable plants such as Rhododendron, Camellia and contained plants, including fuchsias.
Black spot on roses is very common at this time of year, and spraying will no longer be effective. Clear fallen leaves and burn them to prevent spread.
Powdery mildew can be a problem in dry summers.
Leaf drop, disfigured and damaged leaves can be a symptom of weather damage.
Lawns
Raise the blades on the mower before cutting fine lawns. This will help reduce drought stress.
Mow lightly and frequently so that short grass clippings can remain on the lawn during hot summers to act as a moisture-retentive mulch. Excess thatch can be scarified out during autumn maintenance next month. Mulching mowers cut the clippings even finer than normal rotary blades, making the mulch less visible.
Lawns on thin soils may benefit from a high phosphate feed. This will strengthen the roots for winter, rather than encouraging lush top growth that could suffer in the cold and weaken the grass.
Avoid using lawn weedkillers in late summer – they will be more effective in the cooler, damper autumn weather.
Dig over any areas due to be grassed over later in the year. Leave them for a few weeks to allow weeds to re-emerge, and then spray with a weedkiller or hoe off to ensure thorough weed clearance before seeding or laying turf in the autumn.
Summer meadows may need mowing now if they have passed their season of interest, especially in areas of the country where autumn comes earlier. In warmer parts of the UK, spring and early summer meadows that have extended their period of interest well into the summer could be cut now if not done already.
Troubleshooting
Browning of the lawn is very common at this time of year. Don’t water the grass unless absolutely necessary. It will green up when the autumn rains arrive.
Browning can be partially prevented next year by ensuring that the lawn is well scarified, aerated and drained later in the autumn, and that any soil compaction underneath is remedied before the following growing season.
On amenity and garden lawns, discrete brown patches are usually the product of dog waste, urine from female animals, spilt petrol or oil, or weedkiller and fertiliser overdosing.
On finer turf, especially if it is underfed and frequently mown, patches can be the result of disease such as red thread (on sandy soils) and dollar spot (in damp weather). Feeding usually helps eliminate these problems.