Sizzling in the sun (we hope)!
Here are your August gardening jobs with added links if I have more information on the subject. Some of July’s jobs are still relevant to do now if you’ve fallen behind or if the weather’s been bad.
August is usually one of the hottest months, making watering essential. Try to use grey water wherever possible, especially as water butts may be running low. Get friends and family to look after the garden if you are away.
Don’t neglect hanging baskets – deadheading, watering and feeding will help them last through until autumn.
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 improving their appearance.
Hardy geraniums can be cut back a little to remove tired leaves and encourage a new flush of growth.
Buy or order spring-flowering bulbs. Plant bulbs such as Colchicum, daffodils and Madonna lilies (L. candidum).
Deadhead plants such as Dahlias and Penstemon and bedding to prolong the display colour well into early autumn.
Many conservatory and greenhouse pests will be active. Check plants regularly for signs of glasshouse whitefly, leafhopper, red spider mite, mealybugs and scale insects. Clean up fallen leaves and spilt compost from benches and floors to prevent pests and diseases spreading.
Keep an eye on aquatic and marginal plants, removing faded flowers and yellow leaves, and cutting back where necessary.
Continue to deadhead roses, to extend flowering into early autumn. Cut back spindly specimens that have lost leaves a little further when deadheading, to encourage new growth.
Water sweetcorn, peppers, cucumbers, aubergines and tomatoes regularly and feed with high-potash food.
Remove lower leaves on cordon tomatoes and pinch out the top of plants to concentrate the growth into the fruit that has formed – 5-6 trusses per plant.
Pinch out the tips of runner bean plants once they reach the top of their support.
Check for cabbage white butterfly eggs under brassica leaves.
Get rid of diseased and dead foliage around your vegetable crops to stop pests and diseases spreading.
Cut back the foliage and stems of herbaceous plants that have already died back (e.g. bleeding heart).
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 bring them on until they are established.
Feed containers, and tired border perennials, with a liquid tomato food each week to encourage them to bloom into early autumn.
Prune climbing and rambling roses that do not repeat flower or produce attractive hips, once the flowers have finished.
Collect and store seed of hardy annuals and perennials for sowing later in the autumn. Good plants to try include Calendula, Nigella, Cerinthe, Papaver, Aquilegia and hardy Geranium.
If you do no other August gardening jobs, thoroughly soak drought-stressed plants and shrubs, especially newly planted ones. Use grey, recycled or stored rainwater wherever possible.
Top up water where necessary in ponds and water features. Aerate the water in hot sticky weather by leaving fountains on overnight. Continue to remove blanket weed and duckweed using a net or rake.
Keep early flowering shrubs such as Camellia and Rhododendron well watered during dry periods to make sure good flower bud initiation.
Limit the fruits on a squash plant to about three, but make sure these fruits are established before pinching out the surplus.
Lift and dry onions, shallots and garlic once the foliage has flopped over and yellowed. Store them in onion bags to prevent mould developing.
Spring-sown carrots and beetroot will be ready to harvest now although they can be left in the ground to keep growing.
Harvest French and runner beans little and often to prevent them from setting seed. Pick runner beans regularly to prevent them from becoming stringy and to make room for developing pods. Leaving mature pods to set seed can prevent further flowers from developing and reduce your crop.
Continue to harvest second early potatoes now – perfect for salads!
Pinks and carnations can be propagated by layering. Propagate irises by dividing the rhizomes if not done last month.
Rock garden plants, such as Helianthemum, Aubrieta and Dianthus can be propagated from cuttings at this time of year.
On a dry sunny day, collect seeds of herbs such as dill, fennel, caraway and chervil and dry in a warm spot out of direct sunlight. Chervil must be sown immediately.
Keep picking flowers to encourage more flower buds to form and open.
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.
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 container plants including Fuchsias.
Start harvesting your maincrop potatoes as the leaves yellow and die back. Try storing your potatoes in hessian sacks which exclude light but allow adequate ventilation.
Sweetcorn is ready when you can pop a kernel with your thumbnail and the juices are milky.
Keep an eye out for potato and tomato blight and remove and destroy any affected plants to prevent its spread.
Summer prune apple and pear trees to encourage more fruiting spurs – one of the vital August gardening jobs. Put grease bands on fruit trees to catch wingless winter moths.
Sow hardy annuals directly into borders. They will overwinter and flower next summer.
Propagate perennials by dividing once they have finished flowering, but only in areas with some rain and duller weather, to avoid drying out problems.
Don’t cut off the flower heads of ornamental grasses. These will give winter interest.
Don’t be worried by bright green, heavily armoured looking insects on your plants – these are harmless shield bugs which do not need control.
Get in qualified tree surgeons to remove large shrubs and trees that were casualties of winter waterlogging and summer drought. Remove stumps wherever possible, as rots could spread to other plants.
One of the most important August gardening jobs is to keep harvesting courgettes before they become too big!
Ventilate conservatories to their maximum to prevent soaring temperatures. Use shading if necessary. Damp down greenhouses on hot days to maintain humidity levels.
Clearing out fallen leaves and debris regularly from ponds will help to keep down algal growth, as there will be fewer nutrients available from rotting organic matter. Barley straw pads or extract may also be beneficial.
Earwigs can make Dahlia blooms ragged. Catch them in upturned pots crammed with newspaper or straw on canes among the flowers.
Remove and destroy any Nicotiana showing signs of downy mildew. This shows up as yellowish blotches on the upper surface of the leaves.
Take cuttings of herbs such as rosemary, sage or mint now to bulk up supplies. Put cuttings in moist, well-drained potting compost (one part grit to one part compost) and place in a cold frame.
Established clumps of chives can be divided now.
Hebes and lavenders can be given a light prune after flowering.
Give hedges a final trim over now. They will only grow a little before cold weather stops growth.
Plant out rooted strawberry runners and pot some up to bring into the greenhouse later in winter for early fruits.
Vegetables to sow now include lettuces, spinach, land cress, purslane, beetroot, radishes, coriander, spring onions, calabrese, spring greens, turnips for their green tops, Swiss chard, winter spinach and hardy Japanese onions.
For gardening jobs in July, visit my week-by-week page. To work ahead, see my week-by-week jobs page for September.
August gardening jobs updated June 2022