By Ruth Hayes published
Thinking about what to plant in August? The key to planning any garden is to aim for some form of interest and color throughout every month and season of the year.
As summer moves towards its end and we head towards the fall, you might think your options are running out. But, perhaps surprisingly for some gardeners, there are still lots of things you can plant and sow as part of your flowerbed ideas over the coming weeks.
Firstly, there are mature plants ready to bloom that can go in the ground to brighten the coming weeks. Then, you can turn your focus to hardy annual and biennial seeds to sow in anticipation for next year's color.
What to plant in August: top 10 picks for late summer sowing and growing
Dahlias are an obvious choice when it comes to what to plant in August, as they will flower right up to the first frosts and several varieties bring added interest with bronze foliage. You can also rely on long-blooming salvias, astilbes, sunny rudbeckias and gaillardias, asters, sedums and heleniums.
Although the ground may be dry and the sun fierce right now, you can still plant in the soil as long as you keep everything well watered. Alternatively, if your beds and borders are already full, pop some plants in containers.
The importance of regular watering, especially with new plants, can't be stressed enough. It is crucial that plants are well hydrated as they get established as dehydration will hamper growth and weaken the plants. We have a dedicated guide on watering plants that's full of top tips.
Delicious dahlias are one of the most diverse and long-flowering perennials, guaranteeing you color and interesting leaves from midsummer until deep into the fall. And August is a fine time to plant them out.
They are renowned for their glossy petals in a myriad of dazzling colors, as well as their huge range of shapes and styles, from little pom-pom heads to dinner plate-sized blooms.
An added bonus is that dahlias are as happy as part of your container gardening ideas as they are in the soil, as long as they are kept fed and watered. In fact, container-growing your plants makes it easier to move them into a greenhouse or porch in winter, when the top growth dies down and the tubers need storing in a tray of compost somewhere frost-free. There's more info on how to grow dahlias in our guide.
Top tip: Earwigs will munch through dahlia flowers and leaves. To catch them, fill a small plant pot with newspaper and upend it on a stick near your plants. Earwigs will hide in there during the day and you can collect them up and move them elsewhere (try not to kill them as they will eat aphids, an even worse pest).
Fleshy-leaved sedums, also known as stonecrop and ice plants, produce mounds of pretty pink flowers over unusual, pale green stems and leaves. If you're thinking about what to plant in August, they're a great choice.
They love a sunny spot in well-drained soil and look amazing when several are grouped together at the front of a border. They make a good addition to the best drought-tolerant plants too, as once they are established they need little watering.
Plus, because they flower late in the year, often well into the fall, they are an essential source of food for late-flying butterflies and bees.
Top tip: Leave the flowerheads attached through winter as they look beautiful covered in frost. Then cut them back in spring when next year's new growth is starting to show through.
Many ornamental salvias will flower well into the fall, deep purple 'Amistad' being a key variety. So if you're wondering what to plant in August, these are a good choice.
There are more than 900 varieties and they do best on free-draining, sunny soil. Their leaves often give off a delicious herby scent when crushed between thumb and forefinger.
They also grow well in garden planter ideas, which is an added bonus in exposed, northern gardens as they can be moved indoors through winter to continue growing.
Hardy varieties are cut back hard in winter or early spring, while half-hardy plants (check the label when buying) are best cut back in autumn and overwintered in a frost-free greenhouse. If you are not sure of the status of yours, leave pruning until the spring.
They're easy to propagate, too. Just follow these simple steps:
- Take cuttings in late summer or spring. Cut 4in (10cm) long pieces of non-flowering stem and strip away the lower leaves.
- Dip each cut piece in hormone rooting gel and insert into a pot of gritty, watered cuttings compost.
- Cover the pot with a clear plastic bag, then place in a cool greenhouse shielded from strong sunlight. They should be ready to pot on in three weeks.
You can find more tips on how to take cuttings from plants in our feature.
Sunny rudbeckias can flower right the way through to October. They brighten the garden with their chunky, daisy-like blooms in fiery shades of yellow, red and orange – perfect if you love a hot-hued garden color scheme.
Also known as black-eyed Susan, they like a sunny spot and are one of the easiest plants to grow, with annual and biennial varieties such as double-petalled 'Cherokee Sunset' and 'Aries' started from seed in spring, and perennial 'Herbstone' and 'Goldsturm' planted at any time of year.
Mature clumps of perennial varieties that are four or five years old can be lifted and divided in spring or autumn.
Top tip: Most perennial rudbeckias come in shades of yellow, while annual varieties grown from seed generally have more varied coloring, with dramatic burnt oranges and reds often available.
If you can't stand the heat, avoid growing crocosmia, because these red, yellow and orange beauties will add plenty of fire to your borders.
Also known as montbretia and hailing from South Africa, crocosmia produce their glossy, hanging racemes of flowers above tall, elegant and strappy leaves that take up little room, allowing you to plant lots of complementary things around them.
They can become invasive as they mature and the corms from which they grow start to multiply. Solve this problem by digging them up and dividing the corms, keeping the young, firm ones and discarding those that are old or feel soft and squidgy to the touch.
Top tip: Because they hail from the southern hemisphere, crocosmia are not reliably hardy in northern and exposed gardens, so need mulching with a generous layer of well-rotted compost or manure in late autumn once their leaves have died back. Need more advice? Our ultimate guide to mulching has you covered.
Cornflowers are easy to grow and are a lovely choice for cottage garden ideas. Their seeds are either sown now or next spring, though those that go in the ground this year may flower before those that are started the next, giving you a longer succession of flowers.
As well as the traditional blue shade, they also come in a variety of colors including the deep 'Black Ball' and pink, blue and mauve 'Polka Dot'.
They like a sunny spot and should be watered regularly during dry spells. Deadhead too, to keep plants producing more buds all summer long.
Once flowering has finished, you can leave the plants to self-seed, or collect the seeds and sow them where you want them to grow instead. There are more tips on how to grow flowers from seeds in our guide.
Top tip: Weed around the plants while they are growing, as weeds will smother them and steal food, water and light.
Related to perennial delphiniums, larkspur is another traditional hardy annual that is so easy to grow and will also happily self-seed around your borders in August and September. And, while some plants become a nuisance when they spread themselves about, these tall beauties with their delicate flowers are more than welcome.
They get their name from the pointed rear petal, or 'spur' on each flower, and bloom in shades of blue, pink, mauve and indigo.
Top tip: Larkspur have sturdy stems, which makes them ideal for indoor arrangements and bouquets. In a vase, make sure the leaves are above the waterline or they will rot and shorten the time the flowers are viable. Looking for more of the best cutting garden flowers? Our feature has plenty of stunning suggestions.
8. Cerinthe, or honeywort
Cerinthe major 'Purpurascens', also known as the much-easier to remember honeywort, is a striking plant that is one of the best, if not the best, annual bee-friendly plant. And, if you're wondering what to sow in August, this is one of the top picks.
The plant has attractive silver-gray leaves and the flowers are intriguing, tumbling heads of petals in shades of blue and purple.
The large, triangular seeds are easy to collect in late summer and autumn so you can sow them wherever you wish.
Top tip: Although honeywort can tolerate light or dappled shade, they will grow tall, weak and leggy if they don't get enough sun or are crowded out by other plants.
These tall, jaunty plants with their long heads of purple, pink or white bells are one of our favorite biennials and one of the best cottage garden plants.
If sown now, they will grow an immature rosette of leaves and put down roots before winter, then bed down and sit out the winter before resuming growth next spring. They will flower next summer, then set seeds (they are prolific self-seeders) and die back.
Foxgloves are easy to grow, liking light, well-drained soil in a sunny or lightly shaded spot. In the wild they are usually seen in hedgerows and lightly dappled woodland.
You can either sow them where you want them to grow or start them off in pots and modules, overwintering them in a cold frame before planting out next spring.
If you're looking for early summer drama and color when it comes to what to plant in August, try your hand at sowing hardy annual poppies.
They come in a range of shades, from brilliant scarlet to dusty purple. Some are single-petalled whilst some are frilly pom-poms, so there is a poppy out there to suit your space and needs.
As we know from seeing them grow in the wild, poppies will thrive in even poor soil and are happy to be left to their own devices. However, they will do best in a sunny, free-draining spot, so if you garden on heavy clay, open up and enrich your soil by digging in some grit and lots of well-rotted compost or manure.
Scatter the seeds in careless arcs and drifts to create a natural look, and try sowing some cornflower and corn cockle at the same time as they are neutral neighbors when growing in the wild.
Top tip: To collect poppy seeds, wait until the pepperpot seedheads are brown and dry and rattling, then cut them from the stem and carefully empty their contents into a pot or envelope. That way, you'll get more flowers for free – perfect if you're on the lookout for free garden ideas.
Top tips for sowing hardy annuals and biennials in August
Before you sow hardy annuals or biennials, you need to create a seedbed that will provide the best growing conditions for germinating seeds and young plants.
Clear an area of stones, weeds, old roots and other debris and rake it until you have created a fine tilth. This is when soil becomes light and crumbly and has the consistency of a crumble topping.
Water the ground and scatter the seeds thinly before covering them with a thin layer of soil. Don't worry if the seedlings grow close together, you can thin them out later on.
Top tip: Protect sown seeds from hungry birds – and cats that want to use the spot as a toilet – by laying a lattice of twigs over the top. Or, deter pests with a harmless but unpleasantly scented (to them) pepper spray. And on the topic of pests, don't forget we've got plenty of advice on how to get rid of slugs and how to get rid of aphids in our dedicated guides.
Ruth is the gardening editor of Amateur Gardening magazine and spends her working days carrying out, writing about and photographing the tasks the readers should be carrying out each week, as well as testing many of the new products that arrive on the gardening market.
She is horticulturally trained, with a qualification from the Royal Horticultural Society, and her work varies with the seasons and includes everything from sowing and planting, to pruning, taking cuttings, dealing with pests and diseases and keeping houseplants healthy. She covers ornamental plants and edible crops and everything she writes about and photographs is in her own garden, a mature plot that has been a work in progress since her family moved to their current house in 2012.
Her main interests are gardening for wildlife and organic gardening, as she firmly believes you don’t need to ‘nuke’ pests and problems with toxic chemicals, nor use peat composts to produce the garden of your dreams.
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