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Late flowering: the Chelsea flower show is finally back – but what will it look like in autumn?

<span>Photograph: Alamy</span>
Photograph: Alamy

Say what you like about the Chelsea flower show – expensive, crowded, a little superficial? – the Royal Horticultural Society’s annual spring fixture wields considerable influence over gardening trends. Before the pandemic, only two world wars suspended the event. Covid-19 not only cancelled Chelsea 2020, but this year booted the springtime institution into an entirely new season: autumn. That’s the horticultural equivalent of Wimbledon on ice.

The RHS’s decision to postpone showtime until next week was made at the beginning of 2021, giving its designers only months to reimagine their long-proposed show gardens with late-performing blooms. Out with Chelsea staples such as primula, poppy, allium and iris, the surging greens and pastels that evoke the newness of spring; in with bolder tones, deepening leaves, hanging fruit and setting-seeds.

Spikenard berry cluster.
Spikenard berry cluster. Photograph: Alamy

For gardeners, September is one of the busiest times in the calendar, a time of bulb ordering, bed-mulching and making plans. But gardens such as Great Dixter and Hauser & Wirth’s perennial-heavy Oudolf Field show that there’s more to the late season than dahlias and deadheading. Beauty abounds in the russet colours of maturing stems and petals. Trees are in fruit; designer Tom Massey has created a Yeo Valley Organic Garden for Chelsea featuring medlar and quince.

Encouragingly, while the peonies and Pimm’s were put on hold, an estimated 2.2 million new gardeners turned to the trowel during lockdown. If ever the nation was up for a bit of autumnal gardening inspiration, it’s now. So what can we expect from a September equinox Chelsea? And given the show’s influence, which plants are likely to dominate the nursery shelves in years to come?

Designer Jonathan Snow, preparing for his Trailfinders-sponsored garden inspired by the landscapes of the Himalayan foothills, has been eyeing up leafy subtropicals. “The garden’s going to be very lush – not quite jungle, not quite forest, but somewhere in between.” His revised planting list includes the attractive ginger lily Hedychium coronarium, with its upright aromatic stems and bright white flowers, and the closely related, hot-coloured Cautleya spicata. In keeping with Snow’s “Himalayan natives” theme, a range of persicarias will add a prominent flush of deep pink to the garden, from tough and reliable Persicaria amplexicaulis to the massive 5ft annual P. orientalis. With their long-flowering season, persicarias hold their colour well into autumn, and are unbeatable as hard-wearing, weed-suppressing ground cover.

Meadow rue (Thalictrum delavayi), a delicate perennial with glaucous, feathery leaves, is likely to rank among the Chelsea highlights. It will feature in the Guangzhou Garden, co-designed by Peter Chmiel and Chin-Jung Chen of Grant Associates to demonstrate sustainable future city planning. Accompanying their innovative, wildlife-embracing architectural structures and “air and water-cleaning” landscape management initiatives, T. ‘Splendide White’, together with Sanguisorba tenuifolia var. alba, will bring elegance to the planting. “Both plants are native to China,” Chmiel says. “They’re attractive to bees, butterflies and other pollinators, and provide height while allowing visual transparency across the garden.” Eastern sanguisorbas such as S. tenuifolia are fantastic for damper soils. Their fernlike foliage and floaty cat’s-tail flowers feel fresh even in late summer.

For landscape architect Robert Myers, designer of a Florence Nightingale-themed medicinal garden, the seasonal change is a chance to showcase one of the lesser-used, late-blooming shrubs, Heptacodium miconioides. “It’s just perfectly suited to that time of year, with its lovely shaggy bark and scented flowers. You can either grow it as a big multistem shrub or train it as a tree – nurseries seem to be growing it suddenly, which they weren’t 10 years ago.”

Thalictrum Splendide.
Thalictrum Splendide. Photograph: Alamy

One of the notable differences at Chelsea this year will be the inclusion of those wonderfully intense, thuggishly bold prairie perennials: the echinaceas, rudbeckias, heleniums and asters that come into their own as autumn approaches. Far from the soft, greener tones of spring, these North American daisies range across a summer’s spectrum of blazing reds, magenta, orange and yellow. I’m thrilled that Ratibida columnifera, my favourite of the prairie coneflowers, will be making an appearance. It’s a smaller wildflower known for its conspicuously protruding cone and drooped maroon petals.

Hand in hand with prairie plants come ornamental grasses. Stipa, panicum and pennisetum have featured in spring show gardens past, but their colours become amplified by September. “That’s when grasses really come to life,” Tom Massey says. “They start to take on gold, red, buff hues.” One of his favourites is the purple moor grass, Molinia caerulea subsp. caerulea ‘Heidebraut’: “It’s a good form of molinia. The stems go a vivid orange at that time of year, backlit by the early autumn light.”

Ornamental grasses will be a prominent feature for designer Naomi Ferrett-Cohen, too. This year her garden pays tribute to the resilience of the NHS. “I want people to feel enveloped by the space,” she says, “and I think when you walk through grass borders and perennial plantings, you feel quite secluded.” Grasses for Ferrett-Cohen have a “softness and tactility”, such as Stipa gigantea with its arching sprays of golden oats. Stipas are notorious self-seeders in gardens, particularly if planted in gravel or grit, but make an ideal, naturalistic accompaniment to vibrant prairie perennials.

Related: Behind the scenes at the flower shows

Spring may be draped with blossom, but autumn is the season of harvest. Beyond September’s deepening colours, this means berries, fruit, hips and seedheads. Having merged their practices, designers Charlotte Harris and Hugo Bugg placed year-round seasonality at the heart of their first Chelsea garden together, a public “pocket park” designed as a restorative city oasis. They’re excited, therefore, that plants retained from their original spring scheme will have transformed for the coming season. “Our Aralia cordata should hopefully be berrying; the Rosa glauca will have rosehips; the Bergenia ciliata will be reddening,” Harris says. Rather admirably, they’ve even preserved the seedheads of their spring-flowering Tulipa sprengeri, which will be added among the planting. “Sometimes the criticism with Chelsea is, ‘But are these real gardens?’ So this is an amazing opportunity to show that when gardens move into autumn, things senescing and going over can be really beautiful.”

This emphasis on seasonal continuity is appealing. Whether or not this autumn show will prove a one-off, the result may be that the Chelsea garden mindset shifts to something more grounded and realistic, continuing the thrill and promise of a spring garden through to the cooler, darkening days beyond.

• Matt Collins is head gardener at the Garden Museum in London. Chelsea flower show runs from 21-26 September.