At a glance
August is simultaneously the most abundant and the most demanding month in the UK garden. The vegetable plot is at its peak – courgettes, beans, tomatoes, cucumbers, sweetcorn and summer squash are all cropping together, and the harvesting alone becomes a daily task. Borders are full and need deadheading and staking to keep them looking their best. Early sown salad is bolting in the heat and needs replacing with new autumn sowings. And beneath the abundance, the first signs of the season turning are already present – nights are getting cooler, the light is beginning to change, and the window for sowing crops that will crop before the first frost is narrowing rapidly.
Getting the most from August requires working in two directions at once: harvesting and maintaining what is already growing, while simultaneously sowing and planting for autumn. The gardeners who have salad leaves, spinach, spring onions and radishes cropping into October and November are the ones who made their August sowings on time. This guide covers both directions in full.
Vegetable garden jobs
Harvesting is the single most important task in the August vegetable garden. Crops left to overmature on the plant signal the plant to stop producing and divert energy to seed set. Courgettes in particular must be picked every two or three days – a courgette missed for a week becomes a marrow, and the plant stops setting new fruit until it is removed. French beans and runner beans have the same response – pick them young and frequently to keep the plant producing. If you have a glut of beans, freeze the surplus rather than leaving them to toughen on the plant.
Tomatoes need consistent watering in August to prevent the blossom end rot and fruit splitting that follows irregular moisture supply. Water the base of the plant rather than overhead, maintain a thick mulch of compost around the roots to retain moisture, and feed weekly with a high-potash liquid tomato fertiliser. Remove any leaves below the lowest truss to improve airflow and light penetration to the developing fruit. Pinch out the growing tip of cordon varieties once five or six trusses have set – in the UK, fruit that sets after mid-August rarely has enough warmth to ripen before the season ends.
Continue earthing up any maincrop potatoes where the foliage is still upright. Check the foliage of potato and tomato plants carefully for the first signs of blight – brown patches at the leaf margins that spread rapidly in warm humid conditions. If blight is identified, cut the affected foliage off and remove it from the garden immediately. Do not compost blighted material. Potatoes in the ground are usually safe for another few weeks even after blight strikes the foliage, but harvest them promptly if the foliage is heavily affected.
What to sow in August
August is the last realistic window for sowing many autumn salad crops. The combination of warm soil, adequate moisture and still-long days allows rapid germination and establishment before the cold reduces growth to a crawl. Sowings made in late August in a sheltered bed or under cover will crop from October onward and provide fresh leaves through much of the winter with protection. Sow salad leaves, spinach, spring onions and radishes as soon as space becomes available – even a small gap left by a harvested courgette or removed bolted lettuce is enough to fit a short succession row.
Borders and flowers
Deadheading is the most important border job in August. Removing spent flowers from bedding plants, dahlias, sweet peas, roses and most herbaceous perennials prevents energy being diverted into seed production and encourages the plant to produce a further flush of flowers. Sweet peas in particular will stop flowering almost entirely if pods are allowed to develop – pick flowers and remove pods daily for continuous bloom into September. For roses, deadhead to just above a leaf joint with five leaflets rather than simply snapping off the spent bloom, which stimulates stronger new growth.
Take cuttings of tender perennials now to ensure stock for next year. Pelargoniums, fuchsias, penstemons, salvias and osteospermums all propagate readily from semi-ripe cuttings taken in August. Take 8-10cm cuttings just below a leaf node, remove the lower leaves, and insert into gritty compost in small pots. Keep in a warm, sheltered spot – a cold greenhouse or a sheltered windowsill indoors – and they will root within three to four weeks, providing free plants to overwinter and grow on next spring.
Wisteria benefits from its summer pruning in August – cut back the long whippy new shoots produced since June to five or six leaves from the point where they join the main framework. This channels energy into the flowering spurs that will bloom next spring, and keeps the plant within its allocated space. A second pruning in winter completes the two-cut system that keeps wisteria productive and manageable.
Fruit garden jobs
Summer-fruiting raspberries finish their crop in August and should be cut back immediately after the last fruits are harvested. Remove all the canes that have just fruited – they will not fruit again – cutting them to ground level. Select the strongest five or six new canes from each plant, tie them in to the support wires, and cut out all the weaker new growth at ground level too. This gives each cane adequate light and airflow through the winter and produces the best fruiting canes for next season.
Strawberry runners produced abundantly through summer can be pegged down into small pots of compost sunk into the soil alongside the parent plant. Once rooted – typically three to four weeks – they can be severed from the parent, potted on, and grown on to plant out in September for fruiting next year. This is the most economical way to maintain a productive strawberry bed, replacing older plants that have been cropping for three or more years with vigorous new stock from the same variety.
Water established trees and shrubs during prolonged August drought. Many gardeners assume that trees and shrubs do not need watering, but trees planted within the last two or three years have not yet developed a root system extensive enough to source water from deep in the soil profile. A prolonged dry August can cause significant stress and even death in recently planted specimens. A thorough soaking at the base of the tree once a week during a dry spell – rather than a small amount every day – encourages deep rooting and is far more effective than frequent light watering.
Lawn care
August is usually the month when UK lawns show the most stress from drought and heat. Browning off is normal and the lawn will recover as soon as autumn rain arrives – grass is remarkably resilient and a lawn that looks dead in August will be green again within a fortnight of decent rain. Resist the temptation to feed a stressed lawn in August – nitrogen applied to drought-stressed grass can cause leaf scorch and does more harm than good. Hold off on autumn lawn feed until September when the grass is actively growing again.
Keep mowing if the lawn is growing, but raise the cutting height slightly in dry spells – longer grass shades the soil, retains moisture better and recovers from stress more quickly than a closely mown surface. Do not scalp the lawn in a drought. If the lawn has areas of moss or thatch, late August is a good time to plan the autumn scarifying and aeration programme – scarifying and aeration done in September, when the ground is still warm and autumn rain is beginning, gives grass the best conditions to recover and thicken up before winter.
Pests and diseases to watch
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