This story was produced by our colleagues at the BBC.

It’s 5 a.m., and I’ve just entered London’s New Covent Garden Market — the United Kingdom’s largest flower market — from the parking lot. I’m greeted by bright lights and rows upon rows of blooms: Italian ranunculus, Dutch tulips, eucalyptus and English ivy. This place has it all. (Kind of reminds me of a place David Brancaccio visited not too long ago.)

The roots of the New Convent Garden Market stretch back to the 17th century and, these days, it shifts $50 million of flowers annually. And I’ve gotten up at the crack of dawn to find out what goes into all those sales.

First stop: the stall run by Luke Gilbert of Green and Bloom. By now, he’s been awake since midnight, waiting for deliveries from across Europe.

“You never get used to it, though. Doesn’t really get any easier,” he said.

His trick of the trade? Buy fast and stay nimble. Sometimes, he doesn’t know the exact price he’ll pay until the auction in Holland happens just hours before.

“If it goes too high, people just won’t buy it. So you can roughly say how much it’s going to be, but every now and again, we do get some shocks.”

Brexit red tape can be the biggest shock of them all. The U.K.’s split from the European Union has meant lots of fresh border checks. A key one for plants came in last year, with further phases rolling out too. The U.K. government has forecast that border charges could cost British businesses hundreds of millions of dollars a year.

“It’s also affected some of the delivery times,” Gilbert said. “There’s a lot more paperwork they have to go through.”

Further inside, Paul Fairhead from Evergreen Exterior Services is hunched over the counter, surveying his bulbs in pots. His main business is supplying window boxes to offices and pubs across London.

“Brexit has been the biggest pain,” he said. “The government has brought in this new check down at Sevington. They’re taking lorries [trucks] in at 3 o’clock in the morning and pulling them over, but their staff aren’t starting work till 8 o’clock in the morning. So the lorry has been held for five hours,” he said. “We shut at 10 o’clock, so we’ve lost the day’s sales.”

It’s not all doom and gloom, though. I meet Natalie Keller, a florist with a stall in Barnes in southwest London, eyeing a big bucket of colourful tulips to add some color to her bunches.

“I’m normally back to the store for about 9 o’clock,” she said. “We prepare and condition all the flowers and get it out on display for everyone to see and hopefully buy.”

And here’s a trick I picked up today: If the flowers aren’t the right hue, you can always paint them. That’s exactly what wedding florist Susie Ball from Peckham Rye will be doing to her hydrangeas later.

“Because they’re not quite in season, we’ve got to paint them a little bit to get the color right for the event,” she said.

Long nights, early mornings and a constant race against the clock — traders here rely on a delicate supply chain that’s become more complex since Brexit.

Find all of our Tricks of the Trade stories accumulating here.