August Garden Jobs UK: What to Do in the Garden This Month
August is the month when a well-designed garden either sails through to autumn looking magnificent, or quietly falls apart while you are on holiday. The difference comes down to three things: watering deeply and consistently, deadheading to keep the colour going, and making a few smart sowings that will carry you into October.
We have designed and maintained gardens across Kent, Surrey and London for years, and August always separates the gardens that coast from the ones that collapse. It is not about hours of work. It is about twenty minutes every couple of days doing the right jobs at the right time.
This guide covers everything you need to keep an ornamental garden thriving through the hottest, driest month of the year, plus the small handful of tasks that set you up for autumn.
Watering: Deep and Infrequent Beats Daily Sprinkling
The single biggest mistake in August is watering little and often. A light daily sprinkle keeps plant roots at the hot surface and does more harm than good. What works is a proper deep soak two or three times a week, delivered in the early morning or evening when evaporation is lowest.
Water at the base of plants, not over the foliage. Wet leaves in bright sun can scorch, and standing moisture on leaves overnight encourages fungal disease, especially on roses.
Priority order when water is limited
- Containers first. Pots can dry out completely in a single hot day. Daily watering is normal for containers in August, sometimes twice a day for small pots in full sun.
- New plantings. Anything planted this year has not yet developed a deep root system and relies on you entirely. This includes spring-planted shrubs, perennials, and climbers.
- Hydrangeas, camellias and rhododendrons. Shallow-rooted and very thirsty. They show stress fast and struggle to recover.
- Herbaceous borders. Perennials putting on a late summer show, dahlias, salvias, and anything still flowering heavily.
- Established shrubs and lawns. These cope. A brown lawn in August is dormant, not dead, and greens up again with September rain. Do not waste water on it.
How to water efficiently
Use a hose with the flow turned low, or a watering can filled from a water butt. Aim for the soil at the base of the plant and let it soak in slowly. For containers, water until it runs out of the drainage holes, wait five minutes, then water again. The first soak wets the compost, the second actually hydrates the roots.
Mulch helps enormously. A 5cm layer of garden compost, bark chips or well-rotted manure over the soil surface reduces evaporation and keeps roots cooler. If you did not mulch in spring, it is too late to start now, but put it on the list for next March.
Deadheading: Five Minutes Every Other Day
Deadheading is the single most effective job for keeping an ornamental garden looking good through August. Removing spent flowers stops the plant diverting energy into seed production and encourages a second flush.
What to deadhead
Roses: Cut back to just above a leaf joint with five leaflets, not just snapping off the dead flower. This stimulates stronger new growth and more blooms.
Dahlias: Snap off spent blooms every couple of days. They are prolific flowerers but only if you keep on top of the deadheading.
Salvias, penstemons, geraniums (perennial types): Shear back faded flower stems to the base. Many will push out a second round of flowers in September.
Sweet peas: If you are growing these, deadheading is non-negotiable. They stop flowering almost entirely once seed pods develop. Pick flowers daily and remove any pods.
Bedding and container plants: Petunias, lobelia, begonias, busy lizzies. A quick tidy every few days keeps them flowering into September.
What to leave
Not everything should be deadheaded. If you want rose hips for autumn interest, leave the last flush of roses to set fruit. Fennel, teasels, rudbeckia, echinacea and sedums all have seedheads worth keeping, both for structure and for the birds that feed on them through winter.
Feeding Container Plants Weekly
Anything growing in a pot or hanging basket is running on empty by August. Compost loses nutrients quickly with repeated watering, and by mid-summer most container plants are starving.
Feed weekly with a liquid fertiliser. For flowering plants, use a high-potash tomato feed. For foliage plants and ornamental grasses, a balanced liquid feed works better. Dilute as per the bottle instructions and water it in after a normal watering session, never onto dry compost.
Stop feeding permanent shrubs in pots by the end of the month. Late feeding pushes out soft new growth that will not harden before the first frosts and gets scorched in October.
Summer Pruning: Wisteria, Climbing Roses and Lavender
August is the traditional month for summer pruning, which is different from the hard structural pruning you do in winter. Summer pruning is about tidying, shaping, and channelling energy into next year's flowers.
Wisteria
Cut back the long whippy shoots produced since June to five or six leaves from the point where they join the main framework. This encourages the short flowering spurs that bloom next spring and keeps the plant within bounds. A second pruning in January completes the two-stage system.
Climbing roses (rambling types that flower once in early summer)
Once flowering finishes, cut out a few of the oldest stems entirely and tie in the new growth. This keeps the framework young and vigorous. Do not prune repeat-flowering climbers now; they will have more flowers coming.
Lavender
Trim lavender in late August once the flowers have faded. Cut off the flower stalks and take a couple of centimetres of the leafy growth with them, shaping the plant into a tidy mound. Never cut back into the old bare wood. Lavender rarely regrows from it, and you will end up with a brown skeleton.
Hedges
Give formal hedges (box, yew, beech, hornbeam) their final trim of the year in August. Check for late-nesting birds first. If you find an active nest, wait. Most birds have finished by now, but the odd late clutch does happen.
Sow Salad Leaves, Spinach and Spring Onions for Autumn
Even if you do not grow vegetables, a small patch of salad leaves, spinach and spring onions is worth having. August is the last realistic window for sowing crops that will give you fresh leaves into October and November.
The soil is still warm, germination is fast, and the shortening days slow bolt-prone crops like lettuce and spinach, letting them grow steadily rather than rushing to seed.
What to sow now
- Salad leaves and lettuce: Hardy varieties like 'Winter Density' or mixed salad leaf blends. Sow direct or in modules.
- Spinach: 'Medania' and 'Perpetual' spinach are reliable. Sow in rows or broadcast in a patch.
- Spring onions: 'White Lisbon Winter Hardy' crops from October onwards.
- Rocket and mizuna: Fast-growing, peppery leaves for salads.
- Radishes: 'Cherry Belle' or 'French Breakfast'. Ready in 4-6 weeks.
Sow in a sheltered spot or in a cold frame if you have one. Cover with fleece if nights turn cold in September. Even a small 1m x 1m patch will keep you in fresh leaves through the autumn.
Pests and Diseases: What to Watch For
August's warm, often humid conditions are perfect for pests and fungal diseases. A quick check every few days catches problems before they spread.
Powdery mildew
White powdery coating on leaves, common on roses, phlox, asters and courgettes. Caused by dry soil and poor air circulation. Water at the base, not the leaves, and thin out congested growth. Remove affected leaves. Feed to strengthen the plant.
Black spot on roses
Black or brown spots spreading across rose leaves, which then yellow and drop. A fungal disease worse in wet, humid conditions. Pick off affected leaves immediately. Rake up and bin any fallen leaves (do not compost). Mulch to prevent rain splash from soil onto lower leaves. Feed roses to encourage strong new growth.
Vine weevil
Adult beetles notch the edges of leaves (ugly but not fatal). The real damage comes from the grubs, which eat plant roots through autumn and winter. Check containers for C-shaped white grubs with brown heads. Treat pots with a biological control (nematodes) watered in during August and September when soil is warm.
Aphids
Clusters of greenfly or blackfly on soft new growth, especially roses, dahlias and beans. Squash by hand or blast off with a hose. Encourage ladybirds, lacewings and hoverflies, which eat aphids by the hundred. Avoid insecticides, which kill beneficial insects as well as pests.
Jobs NOT to Do in August
Do not plant new shrubs, trees or perennials
Hot, dry soil is the worst possible environment for establishing new plants. They struggle, wilt, and rarely thrive. Wait for autumn. September and October planting, when the soil is still warm but rain is more reliable, gives far better results.
Do not prune spring-flowering shrubs
Camellias, magnolias, lilacs, philadelphus, weigela and flowering cherries have already set next year's flower buds. Pruning now means cutting off next spring's display. Prune these immediately after flowering finishes, which for most is May or June.
Do not cut back herbaceous perennials yet
Leave the tidy-up until October. Cutting back now removes foliage the plant needs to build energy reserves for next year. It also removes habitat for beneficial insects sheltering through late summer.
Lawn Care in August
If your lawn is brown, do not panic. It is dormant, not dead, and will green up again with September rain. Browning is the lawn's way of surviving drought, and it works.
If you must mow, raise the blades to the highest setting. Scalping a stressed lawn in August does lasting damage. Better still, leave it alone and mow properly again in September.
Do not feed, scarify, or aerate the lawn in August. These are autumn and spring jobs. August lawn care is hands-off.
What This Month Sets You Up For
The jobs you do (or skip) in August determine how your garden looks in September and October. Consistent watering and deadheading keep the display going. Summer pruning keeps climbers and hedges in shape. The small sowings you make now provide fresh leaves when the shops are full of imported salad flown in from Spain.
August is not about long days in the garden. It is about short, focused sessions doing the right things. Twenty minutes every other day beats three hours at the weekend and a week of neglect.
We work across Kent, Surrey, Essex and London helping clients keep their gardens looking their best year-round. If you would like help with planting plans, seasonal maintenance advice, or a full garden design, get in touch for a free consultation or call us on 0203 834 9807.
Frequently Asked Questions
What are the most important garden jobs in August UK?
The core August jobs are deep watering two or three times a week, deadheading roses, dahlias and perennials every few days, feeding container plants weekly, summer pruning wisteria and lavender, and sowing salad leaves and spinach for autumn. It is a month of maintenance rather than major projects.
Should I water my garden every day in August?
Generally no. A deep soak two or three times a week is better than daily light watering, because it encourages deep root growth. The exception is containers, which can dry out in a single hot day and often need daily watering, sometimes twice a day for small pots in full sun.
When should I trim lavender in the UK?
Late August is ideal, once the flowers have faded. Cut off the flower stalks and a couple of centimetres of leafy growth to shape the plant into a tidy mound. Never cut back into old bare wood, as lavender rarely regrows from it. This keeps the plant compact and encourages fresh growth for next year.
What can I plant in August in the UK?
August is a poor month for planting shrubs, trees and perennials, which establish far better in the cooler, wetter conditions of autumn. It is a good month for sowing fast-growing salad crops like lettuce, spinach, rocket, spring onions and radishes, which will crop into October and November.
Why is my lawn brown in August?
Brown grass in August is almost always drought dormancy, not death. The lawn shuts down to survive dry conditions and greens up again with September rain. Do not waste water on it. Prioritise containers, new plantings and thirsty shrubs instead.
What should I deadhead in August?
Deadhead roses, dahlias, salvias, penstemons, geraniums (perennial types), sweet peas, and bedding plants like petunias and lobelia. Removing spent flowers stops the plant setting seed and encourages a second flush. Leave seedheads on rudbeckia, echinacea, fennel and sedums for autumn structure and bird food.
Can I prune roses in August?
Yes, but only to deadhead and tidy. Cut spent flowers back to a leaf joint with five leaflets to encourage more blooms. Do not do major structural pruning now. That is a late winter job (February or March). Climbing roses that flowered once in early summer can have old stems removed and new growth tied in.