The plantswoman and entrepreneur Sarah Raven spoke to Tiffany Daneff all about dahlia trends and gives advice for the best colours to use in 2019.

The oak table at Perch Hill Farm in East Sussex, where the writer and florist Sarah Raven is trying to find space for salad bowl and lunch plates, is crammed with 20 or so small vases, each filled with spidery purple-and-white dahlias. They are an otherworldly discovery, which the plantswoman picked out from the hundreds on display in the dahlia fields of Holland, and will soon be growing in gardens across Britain.

Perch Hill is not only Sarah’s home, but also her laboratory, to which, for 25 years, she has brought back her finds: neon-pink dahlias, acid-green tulips and all manner of brilliantly coloured flowers. To make it into her catalogue, these must do well, last in a vase and deliver plenty of blooms, hence the splendid bucket test that’s a relic of her scientific past (she read medicine at Cambridge).

It involves counting how many buckets of flowers she can pick over a season from a 3sq m planting. ‘Cosmos is my benchmark, at 50 buckets per square metre. If anything is between 30 and 50, you have to take it seriously.’

Rip City, the large wine-dark cactus dahlia she spotted in the early 1990s in Monet’s garden at Giverny, gave 40 buckets and went on to become her first big dahlia success, kick-starting the fashion for deep, dark-red flowers. The next craze was all about boiled-sweet colours: neon pinks,

oranges, acid greens and yellows.

Now, apparently, it’s all change again. ‘Everything is very muted these days, very vintage antique, sort of faded sepia, a bit 1970s, khaki and mustard, very receding colour,’ she notes. Flowers, like fashion, follow the markets.’

Café au Lait is the classic example, she explains of the milky-coffee-coloured dahlia that everyone seems to be growing this year. ‘I’ve loved it for decades, but the two or three times I’ve tried to put it in [the catalogue], we would just get left with thousands. Ten, 15 years ago, we couldn’t sell a dinner-plate-sized dahlia for love nor money.’

The late plantsman Christopher Lloyd always adored brilliance and shocking his visitors with outrageous colour-clashing borders – he was a great champ-ion of the dahlia, then very non-U – but it was Sarah who spread the word, launching her own catalogue so that people could actually get their hands on long-lost varieties and kaleidoscopic new discoveries. There are more than 57,000 dahlia cultivars out there, so it’s undoubtedly a rich seam.

The publication in 1999 of The Bold and Brilliant Garden made her name. Soon, the author was everywhere, a petal machine turning out winning flower combinations, books about how to grow your own cut flowers and courses on the whole plot-to-plate, grow-your-own dream – in short, creating a lifestyle brand before Instagram had even been heard of.

She’s made show gardens at Chelsea, presented programmes on the BBC and, a couple of years ago, was invited onto the RHS Council; she is a gardens advisor at the new RHS Garden Bridgewater. There’s a new book under way (on colour palettes) and next year’s catalogue to shoot, but she’s a self-confessed workaholic who does spin classes to relax.

These days, you can’t move for young women opening cutting gardens, but, 10 years ago, when Sarah was making a BBC film about flower growers, she struggled to find them. It remains a tough business and it’s only in the past four or five years that she’s started earning a decent living from her catalogue sales. Too many things can go wrong – the weather being the most obvious – and many ventures fail.

Having seen how the Dutch subsidise their flower industry, she suggests this is something we could be considering post-Brexit. ‘If you grow a field of wheat or raise sheep, you get a massive subsidy, but if you grow a field of flowers, you get nothing.’

Sarah was a botanist long before she was a gardener. As a child, she would go botanising with her father, spending peaceful, happy times with him until she went away to school at the age of 15. They found crocus and hellebores, the early iris Hermodactylus tuberosa and incredible orchids in the Italian Dolomites. Closer to home, they wandered through fields of oxslips in the acid-rich heathlands of the Breck in Suffolk.

She was only 17 when her father died and it wasn’t until she met Adam Nicholson, the writer, whom she later married, and went on a walking holiday to Crete that wildflowers came back into her life. ‘I fell back in love. I’m not a stamp-collector botanist. I won’t travel to the other side of the world to find some rare orchid. I like spec-tacle and abundance, which is what we found there.’

In 2011, she eventually found the time to produce, with photo-grapher and friend Jonathan Buckley, with whom she has collaborated for almost all of her professional life, her doorstop book Wildflowers, a portrait of her favourite 500 British wildflowers. This involved a lot of driving down bumpy lanes – they managed to break the sumps on both their cars.

‘We couldn’t have done it without the wonderful Wildlife Trusts. I’d know that on the Kent coast there was an early spider orchid and I’d contact the local wildlife trust. They would say “Okay, meet us at the gate on the right of the A20 whatever” and would take you to the best place. We were shown glades of slipper orchids, of which I had only ever seen one in my life, and they were standing knee high. It was absolutely incredible.’