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'Seasonal Compression' Effect to Bring Colour Explosion to Gardens

The Royal Horticultural Society (RHS) is predicting an imminent spectacular surge of flower colour in gardens following an unusually cold April that held back blooms by as much as three weeks. A ‘seasonal compression’ effect could see prolonged spring flowering while delayed summer plants blossom as temperatures are predicted to soar in the coming days – but the phenomenon may not last long.

Last month saw the most overnight frosts in April since records began, in stark contrast to 2020 when the locked-down nation enjoyed the sunniest April ever. While the cold nights and a lack of heavy rain helped preserve spring favourites such as daffodils, tulips and cherry blossom and kept weeds at bay, a warm and sunny spell could now cause late spring and summer flowers to rush into bloom in a matter of days.

RHS Chief Horticulturist Guy Barter explains the compression effect: “With so much growth and flowering held up by the cold April nights, the flowering and growing season can be compressed. This means that when the weather turns around, all the pent-up growth and flowers will come out in a rush leading to a brief but colourful crossover of spring and summer flowers.” However, he cautions that what’s good for garden plants is also good for weeds, and suggests gardeners have hoes at the ready to see off a flush of unwanted growth.

The seasonal phenomenon comes just in time for the first visitors to enjoy the spectacle at the new RHS Garden Bridgewater in Salford, Greater Manchester, which opens on 18 May. The garden team led by Curator Marcus Chilton-Jones has planted around 80,000 bulbs to fill the new beds and borders with spring colour, but sunshine on the way could see summer herbaceous plants and shrubs stimulated into bloom too.

Paul Cook, Curator of the most northerly RHS Garden, Harlow Carr in Harrogate, North Yorkshire, says the flowering season is running as much as three weeks behind. While tulips and daffodils are still looking fresh in the garden, Paul’s team must wait until the frost risk has passed to plant out summer blooms such as salvias, cannas and dahlias.

Visitors will have to be quick to catch the combined spring and summer peak, however: “The cooler weather has definitely boosted the displays of Erythronium (dog’s tooth violet) and Trillium in our woodland,” says Paul. “However, if we have a sudden spell of hot weather, it could see them off in a matter of days.”

Meanwhile, the magnificent blue spectacle of the Camassia meadow at RHS Garden Wisley in Surrey is just coming what could be a short-lived peak. Nearby, however, 45,000 new white-flowered Camassia ‘Silk River’ planted to lead up to the new RHS Hilltop – The Home of Gardening Science, opening in June, have been held up by the cold weather and are expected to burst into bloom in the coming weeks. Wisley’s Curator Matthew Pottage is also hoping that a rare Puya chilensis that has recently flowered in the Glasshouse will hold on to delight visitors who will be allowed back inside from Monday after months of closure.

At RHS Garden Hyde Hall, a demonstration of more than 240 varieties of spring-flowering pansies will be coming to a vibrant peak just as the first of the garden’s roses are expected to flower. The garden’s Curator, Robert Brett, says that crabapple blossom has also had an exceptional season this year, with air frosts having helped the blooms to hold on for longer, while the summer display of rhododendrons and azaleas is also just beginning.

The woodland valley situation of RHS Garden Rosemoor in Devon has sheltered its collection of camellias, azaleas, rhododendrons and magnolias from damaging spring frosts and they are enjoying an extended flowering season. Curator Jonathan Webster is hopeful that the two famous Rose Gardens are on track for a spectacular summer of flower as its annual Rose Festival returns in June after being cancelled last year due to the pandemic.

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This story was published on: 14/05/2021

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