Behind the scenes with the grower to the stars It's a wet Friday afternoon down at the muddy nursery near Hook in Hampshire, where some 60,000 beautifully grown plants are lined up in tunnels and out in the open ground, destined for four main gardens, one artisan garden and 10 trade stands at this year's Chelsea Flower Show. Just six months ago the 15-acre site was part weedy field, with a run-down retail nursery out front and collapsing propagation tunnels behind. Now the field has been cleared and planted out, pots of roses, alliums and grasses have been labelled with the wholesale nursery's classy new name, Hortus Loci, ready to supply the RHS Wisley Plant Centre, Clifton Nurseries and Crocus, as well as the on-site retail plant centre, Whitewater Nursery, which will reopen at the end of June. And finally there is the Plant Arena, Britain's first marketplace of plants being offered to professional garden makers by a selection of some 40 of the leading European and British nurseries, which will open next spring. Plants are in Mark's bloodstream, though his first immersion in the industry was when he left Wellington College at the age of 16 and joined the family wholesale nursery, Roseland, in Chobham, which his Dutch grandfather, John Straver, had started in 1933. At the age of 24 he set up his own garden centre on his father's land and called it, somewhat ambitiously, Mark Straver Specialist Plant Centre. The specialist plants were, he admits, the ones he liked at the time. It was phormiums and cordylines and all the things you daren't admit to anymore. And," he adds, with a chuckle, "I had Ceanothus 'Puget Blue," which was really exotic then." Now his plant list, derived from more than 10 years of seeking out plants for our most discerning designers, is a barometer of current horticultural good taste. He sold his plant centre in his thirties, went travelling for a year and returned to take up a job with Crocus at its inception, originally as the products buyer and then switching to plants buyer. When Tom Stuart-Smith asked if Crocus could supply a full plant list for a job, Mark found himself looking at a spreadsheet that was 1,000 lines long (the garden was Broughton Grange in Oxfordshire). "To source all the plants on a list like this is hugely time consuming, very stressful and you'll get let down with every excuse you can think of," says Mark in his famously direct way. But the good thing is that once you start doing it on a reasonable scale, nursery people start taking notice of you. Requests for supplying Chelsea gardens followed. "Our ethos, which I quickly learnt by doing Chelsea shows, is that there's no such thing as 'no can do," so when I heard, 'Oh, I can't, mate," or, 'Oh no, mate, it's five minutes past five," I immediately got rid of them and surrounded myself with people who can do." He admits to doing a fair bit of shouting and swearing when suppliers don't deliver - a trait that Jinny Blom, who's a close friend, recognises but says, in his defence, "He only uses his appalling temper to get a better result." With his reputation for seeking out only the very best specimens, he soon built up a little black book of top-notch nurseries such as Orchard Dene, Phoenix Perennials, Howard Nurseries, Woottens, Fromefield and Chichester Trees and Shrubs from the UK; Jan Spruyt, Laurica and Solitair from Belgium; Lorenz von Ehren from Germany; and Lepage from France. Finding the plants and keeping an eagle eye on their progress - with the plants that need to overwinter in southern Europe, this means frequent trips to the nurseries - is half the job. The other half, he says, is "managing expectations" - shorthand, I detect, for managing the designers themselves. Some, such as Stuart-Smith and Jinny Blom, have a very clear idea of exactly which species they want; others (naming no names) will say, "I need big, white, towery stuff for a shady spot." Even with experienced designers, he has to scrutinise their lists carefully. "When I discovered that Ulf was expecting his Salvia nemorosa 'Caradonna" to be three feet high - the height they reach at his home close to the Arctic Circle - I immediately let him know that we could not get them to that size here." Designers add to his stress by not coming to the nursery to see their plants or at least phoning to check on progress. And then in the run-up to Chelsea, he says, they all panic. They get to see drawings of all the others and they all think 'mine's rubbish. And in the week before the show opens, it's the Tuesday that's particularly manic as the plants that the designers have usually sent back the day before have to be loaded on to the lorries again, because they've changed their minds. Mark doesn't get annoyed with these last-minute substitutions - it's part of the job - but it is a logistical nightmare. And of course every year there are plants that have either gone over or haven't come far enough on, and the ones that crash off the trolleys or are demolished by reversing lorries. That's partly why Mark grows four times as many plants as will actually be used. Why does he do Chelsea, apart from the obvious financial gain? I have no idea why. It's certainly fun at the beginning, sourcing the plants, but by the time showtime arrives I can't stand the idea of going up there. But then he admits, "It's really important for me that the gardens get a gold. Your whole heart and soul's gone into it and you become friends with the designers because you've been through hell and back with them. This year he's excited by the burnt orange Verbascum 'Petra" with a velvet shimmer grown for Joe Swift. Two grasses have also caught his eye: Molinia caerulea 'Dark Defender," a mid-green grass with elegant leaves and black flower stems that stay on for a full year, raised by Marina Christopher and being grown for Andy Sturgeon's garden; and Deschampsia flexuosa, an "absolutely stunning dark green grass" chosen by Sarah Price for The Telegraph Garden. It's Sarah he picks out as standing a very good chance of winning Best in Show. She's moved away from the obvious Chelsea garden shapes and structure and is using lots of lovely water plants. It's all coming together beautifully," he says. The same could be said for Hortus Loci, which is destined to become a one-stop shop for top landscape architects and designers. Hortus Loci, Hound Green, Hook, Hants (01189 326 495; hortusloci.co.uk)