Have you heard of the Philadelphia Flower Show? For some, this seemed a bit of a stretch. Not so long ago the show (the oldest in the US, dating from 1829 when a group of gentlemen farmers got together to strut their stuff at the Masonic Hall) was fairly buttoned down. This year the lines were wavy, starting with a rollercoaster-shaped entry tunnel projecting underwater scenes of turtles and sharks. The entrance is usually dominated by sedate flower arrangements; this year dendrobium orchids and anthuriums were woven into its panels. Showtime: Philadelphia attracts 100,000 more people than Chelsea Flower Show (ROB CARDILLO) Not far away, beside the Waldor Orchids exhibit, a light show pulsed, drums rolled and volcanoes erupted between hula dancers, while a narrator told the legend of Hawaii's formation. The difference in styles from previous years was palpable, long before truckloads of orchids arrived. Bucket loaders brought beach sand rather than topsoil. The plant palette veered towards the shopping mall, with aglaonemas getting their moment in the (simulated) sun. Some might have questioned the eco-friendliness of focusing on tropicals while the rest of the world worries about global warming, but any grumbling went under the radar. Everyone was too busy luxuriating in the screaming colour scheme. Exhibitors adjusted their offerings accordingly. John Story, of Meadowbrook Farm, is the local go-to guy for forcing plants to perform long before they would generally jump into action. But he was virtually given the year off from trying to coax crabapples and delphiniums to bloom out of sequence. Instead, he focused on ripening cherry tomatoes and kohlrabi for PHS's own City Harvest exhibit. This had a lettuce wall, tomatoes dangling from ventilation tubes, and other innovative urban farming techniques. The display celebrated the PHS's partnership with urban communities, as well as inmates of the Philadelphia prison system, to raise produce to feed families in need. Ticket sales benefited PHS programmes including urban farms as well as Plant One Million, a tree-planting initiative. Most other exhibits leant heavily on exotics, but not everyone followed the flow. For example, Michael Petrie was given a section of the desert island of Lanai as his muse. This suited him fine because he isn't a huge fan of frangipanis, and felt that the show already had plenty of tropical plants. Instead he went for ornamental grass in billowing masses ("It looks like weeds, let's face it," he said proudly), set among lava rock. Using rusty chicken wire to represent the windswept dunes, pyramids of sprockets, brake drum rotors and fly wheels as sculpture, and defoliated succulents to illustrate the dicey terrain, his exhibit stood out, and brought home some trophies. The show gardens could give Chelsea a run for its money, but the real story lies with the amateurs. In particular the Horticourt, where individual growers show off their expertise, is fiercely competitive. Plants there are beyond impressive. Think of Akebono clivias with weird variegation that looks like sunburn streaks. Or Haworthia truncata 'Sizumami," or Aloe descoingsii entered by grower Dr Gerald Barad. "In the wild, it's only the size of your fist," he said, beaming over his Madagascar native, bigger than a beach ball. The Philadelphia area has long been a horticultural hotbed, thanks to the surfeit of estates nearby. But this competitive spirit seems to have spread across the country. From coast to coast, everyone had been revving up their trowel skills to outperform friends and rivals. Of course, there were some of the usual suspects in line for blue ribbons. Dorrance (aka Dodo) Hamilton, the Campbell Soup heiress, always hauls in stupendous topiary, and dominates the "Potsize 10 inches and Over" category. But Mrs Hamilton's plants (such as the 7ft, five-tiered, five-leadered myrtle topiary and Paphiopedilum Invincible 'Spread Eagle" with 13 flowers fully open) are show-stoppers and ticket sellers. They serve as structure around which the smaller entries flock. This year, LT Tran was hoping to beat Mrs Hamilton at her own game. He rolled in an immense 10-year-old boxwood teddy-bear topiary, and looked visibly shaken when he learnt that his rival wasn't even in the running. The show isn't only for adults. Whole classrooms march in. Forty students from the Radnor Middle School lugged plants up to the passers (volunteers who check in entries to be judged). Based on the number of paintbrushes they brandished to primp their potential prize-winners, they are plant geeks in the making. Obsessiveness runs deep. Exhibitors used magnifying glasses to check their entries for blemishes, while the expert judges, who travel from 11 states to select the winners, are given nothing but lunch and a drink as compensation. Some of the exhibitors proudly cart their houseplants in. Others focus on design. A sibling trio composed of Cheryl, Donna and (very pregnant) Karen Richards ("If that baby starts to come out during showtime," one sister warned, "it's going right back in there") transformed a blank deck into an entertaining area. Not far away, students from the Abington High School scurried around to create a preschool front porch garden. Oversized pencils served as pillars and a crayon wreath was hung on the door. Their teacher (who followed her mother around the show floor like a toddler) jump-started the idea to enter. Blood connections run throughout. Most of the set-up team are related to each other. Don Slater, who works on the staging, cut his teeth as a child. He was assisted by his daughter, an archaeology student who flew in from Sheffield University for the gig. Joe Marano, who watched his mother win in the Seventies, oversees the horticulture and design classes. His son, Nick Marano, aged 14, is already a veteran exhibitor in the Horticourt. It gives proceedings a familial, friendly vibe. Next year, exhibitors will apply their creative juices to the word "Brilliant!," as organisers believe it encapsulates the British way of doing things. The website promises that the show will "glow with the majestic beauty and creative genius of Great Britain." No pressure, then. For gardening-obsessed Brits, the show will be a chance to see how their horticulture rates with their cousins across the Atlantic. It will also serve as a reminder that the United States can put on a flower show every bit as thrilling - and enormous - as they can. The Philadelphia Flower Show 2013 will run from March 2-10. For more information, see theflowershow.com