Stretching summer; summer flowering perennials and shrubs

By Andy McIndoe

The summer holidays might have only just started, but along with many gardeners our gardens seem to take a break. After the first flush of roses and the glory of the early perennials our beds and borders can seen rather green and “gappy”. We want to make sure that the garden comes back to life after its green summer slumber. But what can we, as gardeners, do to help? How can we stretch summer and get more from the lovely time of the year when the hard light softens and summer heads towards autumn?

If you keep dead heading those roses and seasonal bedding plants they will keep blooming. You could get several more weeks out of your pots and hanging baskets if you keep them in trim. Keep feeding and watering too, otherwise they will simply run out of steam.

Summer flowering perennials

Penstemons bloom for months and no other plant has such fantastic flower power. Cut off seedheads and tidy the plants cutting back and lax stems by half to encourage new growth that should continue to bloom through autumn, and perhaps even into winter. A liquid tomato fertiliser is ideal for all late bloomers that need a boost; it contains lots of potash which encourages growth and helps to harden growth in preparation for cooler nights ahead.

Penstemon 'andenken an Friedrich Hahn'

If your beds and borders look dull it is worth considering how you can make room for some late summer colour. Our changing seasons mean that some of the reliable late season performers are in full bloom in mid summer, crocosmias, echinaceas, kniphofias and heleniums for example. Some varieties are later blooming and these are worth looking out for.


Dahlias are at their best in late summer and pot grown dahlias can be planted in flower; their bright blooms light up the garden and they make wonderful cut flowers too. In many areas these can be treated as permanent herbaceous perennials, the tubers left in the ground from year to year, rather than being lifted and stored. Good ones include ‘Moonfire’, with amber, red-eyed single flowers, ‘Tally-Ho’, scarlet with golden stamens and ‘Roxy’. She has bright purple blooms with gold eyes carried above deep red-brown leaves. You may come across Dahlia ‘David Howard’ when visiting classic gardens. He’s a lovely amber decorative; wonderful for cutting.

Dahlia 'David Howard'

Dahlia 'Moonfire'

Cottage Garden Summer Flowering Perennials

The cottage garden favourites, Michaelmas daisies are often associated with mildew. There are resistant varieties and these are the ones to choose. Aster x frikartii ‘Monch’ only grows to 60 cm or so and has delicate lavender blue daisy flowers on slender stems. It is mildew free and flowers for several weeks It is light and airy and a useful contrast to sedums such as Sedum ‘Herbstfreude’ whose large flattened pink flowerheads are usually turning to claret by early autumn.

With dark green stems and leaves and a mass of bright blue, yellow centred flowers, Aster ‘Sapphire’ is a relatively new variety that is a real “must have” in any garden. Disease free, it is self supporting and excels in its sheer flower power.

Light airy plants lift any planting scheme, and they are invaluable in the foreground to increase perspective and make the border seem deeper. I think the smaller agapanthus work well in this situation and their sapphire blooms are a welcome sight in the summer garden, they are excellent in pots too. The old favourite ‘Agapanthus ‘Headbourne Hybrids’ is hardier than most and delicate enough to fit in with other perennials.

The tall slender Verbena bonariensis is in a similar class. Slender stout stems carry flowerheads of vibrant purple tiny blooms with orange eyes. Late summer butterflies and bees flock to them to seek out their supply of nectar. On well drained sandy soils this plant seeds freely. In my garden it grows like a weed and, although I remove it by the barrow load, how I bless its dainty blooms in late summer alongside glowing dahlias and the early flame tints of deciduous shrubs and trees.

Some ornamental grasses have similar characteristics. The miscanthus or eulalias are at their best in autumn. Upright in form they carry elegant, fine or ribbon-like leaves on strong stems topped with plume like flowerheads. Natives of Japan they are at their best after a warm summer and they appreciate adequate moisture in the soil. There are many varieties: Miscanthus sinensis Morning Light’ is a graceful form with fine silver green leaves. Plant it alongside a block of sedums for contrast.

When it comes to shrubsthehardy hibiscus are my least favourite at the beginning of the year because they are so reluctant to come into leaf. Their ascending grey branches pretend to be dead until May before creeping slowly into life. They make up for it in late summer with an outstanding display of open trumpet flowers in unexpected colours. Hibiscus ‘Hamabo’ has large single blush-pink blooms with crimson eyes. The ever popular Hibiscus ‘Bluebird’ has single violet-blue blooms with deeper eyes. Both make good planting partners for another hero of the late summer garden, the hydrangea.

Hydrangeas conjure up images of mountainous bushes clothed in large heavy flowerheads in blue, pink and white. In reality the hydrangeas are a diverse group of plants with wonderful foliage and spectacularly beautiful flowers. Some start to bloom in early summer whereas others do not start their display until autumn. The varieties of Hydrangea paniculata come into their own at this time with their large lilac-like flowerheads in cream and white. To perform well these need hard pruning to 60 cm or so (harder in the first year after planting) to encourage vigorous upright stems with magnificent flowerheads. They are ideal to plant behind earlier flowering herbaceous perennial where they can take over in later summer. Try Hydrangea paniculata ‘Unique’ with particularly large creamy flowerheads fading to pink and green, and finally parchment in winter.

If I had to choose just one plant for my garden at this time of the year it would be Ceratostigma willmottianum, the hardy plumbago. Usually growing to around 90cm the dark green leaves usually start to flush burgundy as the sapphire blue flowers stud the branches. It is brilliant at the base of a sunny wall or fence and blooms for weeks. It’s also a fantastic choice for “hatchet pruners”: Cut it back by half, with shears if you like, in February and it will respond with a magnificent late summer performance every year.

Ceratostigma willmottianum 2

In recent years many of us have become spring only gardeners. We head off to the garden centre on a sunny day and buy what is looking good and hence, we have spring gardens with little interest later in the year. By choosing now you are certain to pick plants that are looking good and ones that will help you to stretch summer in your garden in future years.

Butterfly on ceratostigma

Featured Summer Flowering Perennials:

Penstemons, crocosmias, echinaceas, kniphofias, heleniums , Moonfire’, Michaelmas daisies, Agapanthus ‘Headbourne Hybrids’, miscanthus,   eulalias, asters, Hibiscus ‘Hamabo’ , Hydrangea paniculata, Ceratostigma willmottianum, Verbena bonariens, ‘Agapanthus ‘Headbourne Hybrids

Andy McIndoe

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