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Helianthus 'Ms Mars' (Sunflower)

Summer flowers: The best summer flowers to plant

Published: June 18, 2022 at 12:20 pm

Make sure you've got the perfect blooms in the garden for summer. Tom Brown, head gardener and tutor at West Dean College, recommends his favourites. Photographs by Jason Ingram

Tom Brown, head gardener and tutor at West Dean College, recommends his favourite summer flowers – great plants that really deliver in terms of seasonal interest. Here is Tom's list of recommended summer flowers.

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Papaver somniferum ‘Lauren’s Grape’

Papaver somniferum, 'Lauren's Grape'

If you’re going to grow a somniferum poppy, make it this one. Once you’ve tried ‘Lauren’s Grape’ and appreciated its sophistication and sultry, bowl-like, dark-purple flowers, you’ll be forever particular about your poppy selections. I start seed off early in the year and treat it as an annual, although the seedlings will overwinter in free-draining spots. If visitors to the garden don’t relieve me of the blue/green seedheads, they make superb cut flowers to add form to an arrangement; and do save the seed for the following year, once the pods have dried. Height 1.5m. Origin Garden (species from southeast Europe and western Asia). Conditions Well-drained soil; full sun. Hardiness RHS H5. Season of interest Early summer, seedheads persist into winter.

Read more about the best poppies for your garden.

Rosa veilchenblau

Rosa 'Veilchenblau'
© Jason Ingram

I adore this rose not just for its unusual tones of violet-purple and its fruit-scented flowers but for its well-mannered, graceful habit, trained on a wall or fence. Classed as a rambler, this rose is well behaved and not too vigorous, like some rambling roses. A superb flush of flowers appear in early summer and into July, which prove to be quite a talking point when in full swing. I find this rose incredibly versatile in the garden, working well with various colour schemes and associating nicely with most plants. AGM. Height 2.5m. Origin Garden origin. Conditions Moist, free-draining soil; full sun. Hardiness RHS H7, USDA 5a-9b. Season of interest May – June.

Read about the 15 best roses from Sissinghurst.

Begonia luxurians

Begonia luxurians
© Jason Ingram

This architectural, palm-leaved species of begonia, with sprays of delicate white flowers, will not tolerate a frost but will quite happily survive during the winter months with a little protection, say in a frost-free conservatory or greenhouse. When the risk of frost has passed, plant out in a container. Feed and water to achieve an impressive specimen relatively quickly, then enjoy the glorious umbrella-like leaves throughout the summer. Also try to associate it with tropical planting schemes, such as cannas, dahlias, zinnias or Fuchsia boliviana. AGM. Height 1.5m. Origin Brazil. Conditions Well drained soil; full sun to part shade. Hardiness RHS H1B, USDA 10a-11b. Season of interest May until first frosts.

Read more about the best begonias for your garden.

Chamaenerion angustifolium 'Album'

Chamaenerion angustifolium 'Album'
© Jason Ingram

This white rosebay willowherb lends a naturalistic ease to borders, both in its appearance and in the way that it effortlessly moves in the breeze; in this way it is reminiscent of its wild cousin. In my experience, it tends to grow on its own terms. In spring, lime-green shoots appear slightly off centre to where they grew the year before. Certainly not a thug but more of a wanderer through the border, it pops up in and around other perennials and shrubs and does not freely self-seed (at least not for me). Height 1.5m. Origin Temperate northern hemisphere. Conditions Reasonable garden soil, tolerant of clay; full sun to part shade. Hardiness RHS H7, USDA 2a-7b. Season of interest Mid to late summer.

Dianthus carthusianum

Dianthus carthusianorum
© Jason Ingram

Far from the rather dated reputation of the ‘Doris’ pink, this little species of dianthus has bucked the trend and found itself very much in favour, even gracing the catwalk that is the RHS Chelsea Flower Show. These lovely plants, with their small, magenta flowers that are displayed on wiry stems, provide a rare delicacy and effortless, naturalistic quality that other dianthus simply don’t offer. Plant it in a sun-baked position that has reasonable drainage for the best performance. Height 50cm. Origin Southern and central Europe. Conditions Well-drained soil, tolerant of chalk; full sun. Hardiness RHS H7, USDA 5a-10b. Season of interest Summer.

Read more about growing and propagating dianthus.

Campanula 'Kent Belle'

Campanula 'Kent Belle'
© Jason Ingram

This campanula impresses me on many levels; there’s the sheer size of its blooms and the dark intensity of its midnight blue, bell-like flowers, and that’s just for starters. As with most campanulas, ‘Kent Belle’ enjoys a fertile and moisture-retentive soil in the summer and for best results it also needs reasonable light levels. The weight of the clusters of flowers can become heavy for the plant, so support with a little birch or hazel to showcase the blooms to maximum effect. Reliably perennial and deserved of its Award of Garden Merit. AGM. Height 1m. Origin Hybrid of C. takesimana and C. latifolia. Conditions Moist in summer but well-drained soil; full sun. Hardiness RHS H7, USDA 5a-9b. Season of interest June – July.

Read our advice on growing campanula.

Allium atropurpureum

Allium atropurpureum

This is not one of those alliums that increases each year and clumps up beautifully. However, I can completely forgive it this one fault and happily treat it as an annual as the intense, dark-purple flowers work so well with perennials at this time of year. You’ll find the bulbs inexpensive and I would suggest planting them in groups of five to seven and work them through clumps of early summer perennials such as artemisia and nepeta as well as with later-flowering perennials such as phlox to give interest and punch in early summer. Height 1m. Origin Hungary to Turkey. Conditions Moist but well-drained soil; full sun. Hardiness RHS H5, USDA 4a-8b. Season of interest Early summer.

Read our advice on growing alliums.

Geranium pratense ‘Wisley Blue’

Geranium pratense 'Wisley Blue'

This beautiful form of cranesbill or hardy geranium has got some real stature when it flowers, particularly when grown up a domed support of hazel or birch, providing height in the border. Classic, powder-blue flowers are profusely produced in early summer, giving a big burst of colour to mixed plantings. Once the flowers have faded, the plant can be cut to the ground, to enable a fresh flush of foliage to emerge, giving a neat and compact foil for other emerging plants. This, like most geraniums, is very versatile and is quite content in many garden situations and schemes. Height 1.5m. Origin Garden (species Europe and Asia). Conditions Reasonable, well-drained soil; full sun. Hardiness RHS H7, USDA 4a-8b. Season of interest Early to midsummer.

Read about 21 of the best hardy geraniums.

Crambe cordifolia

Crambe cordifolia
© Jason Ingram

I challenge you to walk past a Crambe cordifolia in all its glory and not be blown away by its colossal cloud of small white flowers in early summer. In a mixed border, there are few plants that rival its spectacle. As with delphiniums, I’d advise planting Crambe towards the back of the border, to enable plants that climax later in the season to disguise its deterioration as the summer heat intensifies. The sprays of seeds provide interest following the flowers, but the kidney-shaped foliage is little to write home about. As with most brassicas, Crambe enjoys a fertile garden soil. AGM. Height 2m. Origin Caucasus. Conditions Deep, fertile and moist soil; full sun. Hardiness RHS H5, USDA 5a-8b. Season of interest Early summer.

Helianthus annuus ‘Ms Mars’

Helianthus 'Ms Mars' (Sunflower)

Throughout the summer of 2015 I trialled more than 100 different forms of sunflower and became totally enamoured with the dwarf cultivars. These delivered stems that were long enough for cutting but which required no staking. One that stood out from the crowd was ‘Ms Mars’. Its distinct, pink and claret-coloured flowers are produced profusely on knee-high plants. Like all sunflowers, they give a much-needed boost of colour to our gardens when the heat of summer has drawn some of the vim and vigour out of our displays. Height 50cm-1m. Origin Garden origin (species from USA and Central America). Conditions Moist but well-drained soil; full sun. Hardiness RHS H4, USDA 2a-11. Season of interest July to September.

Read our advice on the best sunflower varieties to grow.

Helenium ‘Sahin’s Early Flowerer’

Helenium 'Sahin's Early Flowerer'
© Jason Ingram

I grow several heleniums but this one stands above all others for sheer flower power. It’s incredibly long-flowering –from July all the way until autumn –beginning life with a strong red and burnt-orange display that rather elegantly fades to a paler orange and yellow colour as it senesces, with the chocolatey brown centres persisting into the winter. This robust form of sneezeweed has the vigour and strength to associate happily with other perennials, grasses and shrubs. AGM. Height 1-1.5m. Origin Garden origin (species from North and Central America). Conditions Reasonably fertile and well-drained soil; full sun. Hardiness RHS H7, USDA 4a-8b. Season of interest Early summer to autumn.

Achillea 'Terracotta'

Achillea 'Terracotta'
© Jason Ingram

Achilleas offer tremendous value for money throughout the summer in gardens. This cultivar works incredibly well because as the flower buds open, they turn from an orange, bronze tone to apricot, then yellow through to cream before the flower is ultimately over. We are often encouraged to leave spent flowerheads for winter interest, but I’d keep cutting until the end of the summer as persistent deadheading will perpetuate the performance of this plant for the majority of the growing season. Height 1-1.5m. Origin Garden origin (species from Europe and Asia). Conditions Fertile but well-drained soil; full sun. Hardiness RHS H7, USDA 3a-8b. Season of interest Early summer until first frosts.

Penstemon ‘Raven’

Penstemon 'Raven'
© Jason Ingram

Among the plethora of penstemons currently at our disposal, this classic cultivar is one that has stood the test of time, and rightly so. Tubular, dark-purple flowers appear throughout the summer and into the autumn and the intensity of the flowers contrast well with vibrant reds, such as Echinacea ‘Tomato Soup’ or Achillea millefolium ‘Red Velvet’. If your garden is in something of a cold spot, strike semi-ripe wood cuttings and overwinter in a frost-free place to ensure successive garden performance for years to come. AGM. Height 50cm-1m. Origin Garden origin (species from America and Mexico). Conditions Fertile, free-draining soil; full sun. Hardiness RHS H3, USDA 6a-9b. Season of interest Summer until first frosts.

Read our detailed advice on growing penstemons.

Nigella papillosa 'Delft Blue'

Nigella papillosa 'Delft Blue'
© Jason Ingram

Once you’ve tried growing Nigella papillosa cultivars you may not want to return to the more familiar Nigella damascena. The beauty of the papillosa nigellas lies both in their exaggerated flowers and their subsequent seedheads, which are simply stunning in their own right and look great in borders. The flowers are unusual with bicoloured blooms of white and deep blue on sturdy stems. Nigellas can be equally successful directly sown into a border or started off in modules and then planted out when the plants are large enough. Height 50cm. Origin Garden origin (species from Spain and North Africa). Conditions Reasonable soil; full sun. Hardiness RHS H3, USDA 2a-11. Season of interest June until August from a spring sowing.

Read more about hardy annuals to grow.

Coreopsis tinctoria 'Roulette'

Coreopsis tinctoria 'Roulette'
© Jason Ingram

This form of Coreopsis tinctoria leapt into my consciousness last summer as it produced prolific sprays of red and mahogany flowers with an upper tier of yellow petals throughout the summer. With glorious blooms held on tall, wiry stems, this tickseed is particularly striking. In established borders, a peppering of this hard- working annual adds drama and interest. I’d suggest planting it in good numbers to give an effortless, natural slant to your borders. Flowers well into the autumn too. Height 1-1.5m. Origin Garden origin (species from North America). Conditions Well-drained soil; full sun. Hardiness RHS H6, USDA 2a-11. Season of interest Summer through to autumn.

Echinacea 'Aloha'

Echinacea 'Aloha'
© Jason Ingram

I’ll be the first to admit that I was very sceptical when I heard that the RHS was trialling new Echinacea as I’d always dismissed the coloured cultivars as novelty and lacking in perenniality. How wrong I was. Five years after the trial began, many have not only survived but thrived at RHS Garden Wisley, putting paid to my concerns about their garden worthiness. This one is particularly tasteful, delivering buttermilk flowers during high summer, which fade to leave a typical cone head as added interest. Try mixing with purple sedums and bronze ornamental grasses. Height 50cm-1m. Origin Garden origin (species from Eastern and Central North America). Conditions Best performance in reasonably deep soil; full sun. Hardiness RHS H5, USDA 3a-8b. Season of interest June to August.

Gladiolus 'Sylvia'

Gladiolus 'Sylvia'
© Jason Ingram

It’s tricky to associate most gladioli with other garden flowers. The exotic blooms scream for attention and dominate their companions. ‘Sylvia’, in common with a number of other dwarf cultivars, is the exception to this rule. I use these little flowers in clumps throughout my herbaceous borders, providing a colourful pick-me-up through the latter part of the season. I’ve started to view them as a summer tulip. Plant them around 100 days before you want them to flower and enjoy a burst of colour when much of the garden is a little tired from the summer heat. Height 1.5m. Origin Garden origin (species from South Africa). Conditions Fertile, free-draining soil; full sun. Hardiness RHS H3, USDA 7a-10b. Season of interest Mid to late summer.

Gladiolus 'Bimbo'

Gladiolus 'Bimbo'
© Jason Ingram

If you enjoy the increasingly popular trend of combining creams, dusky pinks and apricot hues, then this summer corm will make a great addition to your planting schemes. There is an antique, coppery quality to its tones that really makes it stand out from the crowd. As with most gladioli, you should plant from April onwards, in clumps where the plants are to flower, and staggered planting will give a longer flowering period. To ensure perenniality, lift the corms after the first cold spell and store in a dry, frost-free place until the following growing season. Height 1.5-2m. Origin Garden origin (species from South Africa). Conditions Fertile, free-draining soil; full sun. Hardiness RHS H3, USDA 7a-10b. Season of interest Mid to late summer.

Read more expert picks for summer bulbs to plant in spring.

Ipomoea 'Caprice'

Ipomoea 'Caprice'
© Jason Ingram

I trialled several morning glories and they were surprisingly variable in their performance, but this was one of the best blues. Strong growth covered my 2m-high obelisk in foliage and pale-blue flowers erupted all over this plant. It was quite a spectacle, especially alongside some of the less floriferous forms. Avoid over feeding or you’ll end up with lots of leaf and only a few flowers, but other than that, in a sunny position, ipomoeas will provide lots of colour and interest well into the summer and cover up some of those less attractive fences. Height 1.5-2.5m. Origin Garden origin (species from Mexico). Conditions Moist and well-drained soil; full sun. Hardiness RHS H1C, USDA 9a-11. Season of interest July – October.

Read about 21 of the best annual climbers.

Galtonia candicans

Galtonia candicans
© Jason Ingram

Galtonias are widely available but as with a number of summer-flowering bulbs, they’re not used quite as often as they should be. I generally start these bulbs off in pots at the beginning of the year and plant out a strong specimen in the spring. Spikes of tiered, bell-shaped, white flowers appear in the summer and give a boost of colour and elegance to mixed borders and containers. Galtonias work well when planted in small clumps throughout a planting scheme to give an effortless and natural feel to your plantings. They’re also great for containers. AGM. Height 50cm-1m. Origin South Africa. Conditions Moist but well-drained soil in growing period; full sun. Hardiness RHS H4, USDA 6a-10b. Season of interest Late summer.

Vernonia arkansana 'Mammuth'

Veronia arkansana 'Mammuth'

Tall border plants can be hard to get right. They need to provide that essential, back-of-the-border, top tier, while also offering prime flowering performance. Vernonias provide both. I’ve discovered them only recently, and was immediately entranced by these sophisticated and intriguing late-summer stars. With their dark-purple flowers, carried on tall, stately stems, they offer a late burst of colour to a border. Height 1.5-2m. Origin Garden origin (species from Northern and Central USA). Conditions Tolerant of most garden soils with good moisture retention during summer months; full sun. Hardiness RHS H7, USDA 5a-8b. Season of interest Late summer through to autumn.

Helianthus annuus 'Vanilla Ice'

Helianthus debilis ‘Vanilla Ice’
© Jason Ingram

Sunflowers can be troublesome when it comes to their heavy flowerheads and can demand strong staking techniques to see them through the latter part of the summer. ‘Vanilla Ice’ is a more delicate, multi-branched individual, and as such is far less demanding. I grow this highly floriferous cultivar for cut flowers. The stems are wiry and the flowers are very useful in arrangements with other summer blooms, such as yellow zinnias and blue statice. Height 1-2m. Origin Garden origin (species from USA and Central America). Conditions Moist but well-drained soil; full sun. Hardiness RHS H2, USDA 9a-11. Season of interest July – September.

Canna 'Erebus'

Canna 'Erebus'
© Jason Ingram

There aren’t many of these water cannas around and this cultivar of Canna glauca is one of the best in terms of reliable, flowering performance. You can grow it in water margins or water-logged containers, submerging the roots throughout the summer. But it is equally happy flowering in a fertile garden soil. Treat it like any other canna, by allowing the first frost to slightly blacken the foliage and then bring it into a frost-free place for the winter. I have learned not to cut the foliage down until new growth emerges in spring. AGM. Height 1-2m. Origin Garden origin (species from South America). Conditions Poorly drained soil; full sun. Hardiness RHS H3, USDA 7a-10b. Season of interest July until first frosts.

Zinnia elegans ‘Benary’s Giant Wine'

Zinnia Elegans 'Benarys Giant Wine'
© Jason Ingram

I grew a number of taller-stemmed zinnias in 2017, and the ones that stood out head and shoulders above all the others were those from the wonderfully consistent Benary’s range. They are available in a variety of colours, with one to suit almost every taste. This one from the Benary’s Giant Series is a classy plant, with sultry mulberry-coloured flowers. It is perfect grown as a cut flower, but will also have a strong presence in your borders until the first frosts. Height 50cm-1m. Origin Garden origin (species from Mexico). Conditions Moist but well-drained, fertile soil; full sun. Hardiness RHS H2, USDA 9a-11. Season of interest Staggered sowing will produce flowers from July until first frosts.

Tithonia rotundifolia 'Torch'

Tithonia rotundifolia 'Torch'
© Jason Ingram

Tall, vibrant and blisteringly bright- orange flowers appear on this Mexican sunflower as the summer warms up. Grow as an annual and plant in full sun in reasonable garden soil to achieve a strong two metres of growth. Tithonias will keep flowering until the frosts (don’t forget to collect the seed). This is a strong cultivar with consistent dark-orange flowers that are hard to beat in mixed and exotic plantings. They detest the cold so resist planting them out until June. Height 1-2m. Origin Garden origin (species from Mexico and Central America). Conditions Well-drained, fertile soil; full sun. Hardiness RHS H2, USDA 9a-11. Season of interest Midsummer to autumn.

Dahlia 'Black Jack'

Dahlia 'Black Jack'
© Jason Ingram

I’d be more than happy to grow this dahlia for its foliage alone. Its strong architectural, glaucous foliage appears in the early summer and complements a number of garden plants. I’ve grown it alongside the earlier performing Potentilla ‘Gibson’s Scarlet’ to act as a foil to the fiery red blooms. As the year rolls on, very large and rich cactus flowers of the darkest maroon appear on very strong stems. Almost shrub like in its habit, this dahlia works on many levels as a garden plant – a welcome cutting flower too. Height 1.5-2m. Origin Garden origin (species from Mexico and Central America). Conditions Well-drained, fertile soil; full sun. Hardiness RHS H3, USDA 7a-10b. Season of interest July until first frosts.

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Read about designers' favourite dahlias.

Authors

As head gardener at West Dean College in West Sussex, Tom Brown has an avid enthusiasm for great, garden-worthy plants. Tom is also an RHS Show Judge and Herbaceous Committee Member.

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