What to do in the garden in August
August is a month for keeping the summer show going and quietly getting ready for autumn. The main jobs are watering and deadheading, pruning lavender and rambling roses after flowering, trimming hedges once birds have finished nesting, collecting seed, and planting autumn-flowering bulbs. It is also the perfect time to sit down with the bulb catalogues and start planning for spring.
Keep the colour coming
Late summer borders can look either glorious or a little tired, and the difference is often a few minutes of deadheading each day. Keep removing faded flowers from dahlias, salvias, cosmos, rudbeckias and roses, and many will carry on until the first frosts. Water pots daily in warm weather and keep feeding them every week or so. Late summer perennials such as heleniums, asters, Japanese anemones and grasses are just getting going, so this is a good moment to notice where your garden needs more late interest.
For me, August is peak sanguisorba season. Sanguisorba canadensis, one of my favourites, sends up tall, white, bottlebrush spikes now, which light up the back of a border and are loved by bees. If you want more of this kind of late summer movement, my guide to planting a border that looks good all year is a helpful place to start.
Prune lavender
Once lavender flowers have faded, usually in late summer, give the plants a trim. Cut off the old flower stalks and around 2 to 3cm of the leafy growth, keeping the plant a neat, rounded shape. The important thing is to leave some green growth on every stem: lavender rarely reshoots from bare, woody wood, so cutting into old stems can leave gaps that never fill. A trim every year keeps plants compact and helps them last longer.
Prune rambling roses and summer raspberries
Rambling roses flower once, in early summer, on stems made the previous year. Once they have finished, cut out a few of the oldest stems at the base and tie in the long, vigorous new shoots that will flower next year. Leave any ramblers grown for their hips. In the fruit garden, cut the canes of summer-fruiting raspberries that have carried fruit down to ground level, and tie in the strongest new green canes for next year's crop.
Trim hedges
By the end of August most birds have finished nesting, which makes late summer a good time to give hedges their main trim. Plants such as beech, hornbeam, yew and privet trimmed now will make only a little regrowth, so they stay crisp and neat through autumn and winter. Still check for late nests before you start, as some birds breed later into the summer.
Collect seed
Many plants are setting seed now, and collecting your own is a satisfying, free way to grow more. Choose a dry day and snip seedheads of plants such as nigella, calendula, foxgloves, poppies and aquilegias into paper bags. Let them dry somewhere airy, shake out the seed, and store it in labelled paper envelopes in a cool, dry place. Leave plenty of seedheads standing too, as they are valuable food for birds into autumn.
August checklist
Deadhead dahlias, salvias and roses to keep them flowering.
Water pots daily in warm weather and keep feeding.
Trim lavender after flowering, without cutting into old wood.
Prune rambling roses and summer-fruiting raspberries once they have fruited or flowered.
Give hedges their main trim once birds have finished nesting.
Collect seed on dry days and store it in paper envelopes.
Plant autumn-flowering bulbs such as colchicums and nerines.
Order spring bulbs while there is plenty of choice.
Plant autumn bulbs and plan for spring
There is still time to plant bulbs that flower this autumn. Colchicums and autumn-flowering crocuses, such as Crocus speciosus, go in now and will often flower within weeks. Nerine bowdenii likes a warm, sunny spot at the foot of a wall, planted with the neck of the bulb just at the soil surface.
August is also when bulb suppliers have the widest choice for spring, so it is well worth ordering early. I always suggest thinking about where gaps showed up this spring and choosing bulbs to fill them. You will find my favourite bulbs and when to plant them in the September jobs.
Lawns and a gentle look ahead
If your lawn has turned brown in a dry spell, do not worry. Grass is tough and usually greens up again quickly once rain returns, so there is no need to water it. Hold off on major lawn work until September, when cooler, damper weather makes scarifying, aerating and overseeding far more successful. Meanwhile, if you are planning bigger planting changes for autumn, now is a good time to make notes and take photographs while the garden is in full growth. If you would like a second pair of eyes, I also offer planting design and consultations. And if anything slipped by last month, the July jobs are still worth a look.
Quick answers
When should I cut back lavender?
Trim it in late summer, straight after flowering. Remove the flower stalks and a little leafy growth, but never cut into bare, woody stems, as lavender rarely regrows from old wood.
Is August a good time to cut hedges?
Yes, late August is ideal for most hedges, as nesting has usually finished and the light regrowth keeps them neat into winter. Always check for late nests first.
Can I plant bulbs in August?
Yes, August is the time for autumn-flowering bulbs such as colchicums, autumn crocus and nerines. Most spring bulbs are best planted from September onwards.
