Each morning, staff and volunteers arrive at daybreak to prune away dead flowers and water plants, and replace thousands of wilted flowers with thousands of fresh ones. They stay until late at night, cleaning up and troubleshooting.

Dozens of horticultural experts show up to examine plants submitted for competition, accepting some (and registering them with mounds of paperwork) and rejecting others.

And in a command center hidden away from the show floor, volunteers and staff field phone calls and manage emergencies -- such as, during this week's snowstorm, rescheduling visits for 19 tour buses while promoting discounts in the hope of attracting other visitors to replace them.

After 188 years, it's controlled chaos at the Philadelphia Flower Show, the largest and oldest indoor flower show in the world and among the most complicated logistical undertakings at the Convention Center.

The show, which began March 11 and closes Sunday, is powered by more than 3,500 volunteers, staffers, contractors, professional florists and landscapers, amateur gardeners, and a corps of union workers. And by untold dozens of Beiler's doughnuts, said Sam Lemheney, the show's director. He gestured to an open box: "This is critical to the success of the show."

It takes a week to install (and, later, three days to tear down). In that time, Lemheney can be found crisscrossing the floor on a lemon-yellow motorized scooter, managing crises and answering questions.

tom gralish / Staff Photographer
Sam Lemheney on his Flower Show-issue scooter.

Two days before the show opened, it was still a construction zone. Muddy tracks ran across the concrete, between towering heaps of sawdust. (It's always sawdust, not soil; it's lighter, water-absorbent, and easy to sculpt.) Forklifts raced by, creating a sense of constant peril, and workers pushed racks of potted plants from the loading zone to their exhibits.

Lemheney didn't get far on his rounds before a volunteer, Jill Brown, jogged over, waving a plastic pot. "The Ecodome needs 100 of these and I don't know where to start!" she said.

He offered advice, then pressed on. He found Tim Morris of J. Downend Landscaping filling a temporary pond with water.

"Is it holding?" Lemheney asked.

"It's not leaking yet," Morris said with a shrug, watching for a telltale trickle of water across the concrete. "But I tell people, all ponds leak. The thing is, you never know if your pond is leaking or you overwatered your plants."

Ordinarily, Flower Show exhibitors build ponds out of cinder blocks and pond liner. Morris, whose Mondrian-inspired design called for crisp, square lines, made the risky decision to build his from plywood coated in Flex Seal. "If it works, I think you'll see a lot of people prebuilding ponds and bringing them in here," Morris said.

There's lots of room for disaster: a leaky pond or failed bulbs, flowers that bloom too early or too late. Morris said he has about 30 percent more plants than he needed for the show, just in case.

Of course, growers and florists have tricks to make plants bloom when they want and to stay fresh-looking just a little longer.

tom gralish / Staff Photographer
Goto Kazu prepares individual pteridopsida ferns for the Japan Flowers and Plants Export Association exhibit.

At one table, Andy Lemheney, a florist who happens to be Sam's father, was deploying what he said is a favorite florist trick. He was spraying tulips -- 26 dozen of them -- with a product called Crowning Glory that helps them retain moisture.

"It will make the flowers last a week or two longer," he said.

This year's show, with its Holland theme, brought special challenges, including building the Ecodome, a structure imported from the Netherlands in three separate shipping containers. Tulips (some dyed a garish, Dutch-flag blue) were also shipped in by air as a point of Dutch pride. Lars Grims, bleary-eyed, pointed out 11 large boxes of them. "They came in this morning at 5 o'clock," he said. "The driver called me out of bed."

This being Philadelphia, most displays larger than 600 square feet require union labor. That was new to some of the Dutch contributors. "It's been difficult," Grims said. "I'm told it's different outside of this building."

Across the Convention Center floor, the Horticourt, which hosts the show's plant competitions, was also filled with frenzied activity.

Competitors can submit entries on several days before and during the show. Each time, the entry must be "passed" by an expert who confirms the plant is labeled correctly and is show-worthy, then tagged, recorded, and displayed.

Last Thursday, a harried Pete Zale, curator and plant breeder at Longwood Gardens, was working as a passer, dashing from one plant to the next and examining each.

"This one here I'm not sure about. It's in the wrong category," he said. Its pot was too large, he added, pulling out a ruler to confirm it, then flipping through the 62-page exhibitor's guide to identify the appropriate description.

A woman arrived with a miniature Norfolk Island pine, and Zale examined it skeptically, noting some yellowed leaves. He crouched down with a magnifying glass to confirm his diagnosis, then shook his head.

"Spider mites are a big no-no. I don't think I can pass this," he told her. "I'd hate to discourage you in any way, but you'd hate for these things to migrate to other plants."

Samantha Melamed / Staff 
Pete Zale (right) assesses a cactus submitted by Bob Albright of Kimberton for exhibition in the Flower Show.

Next up was Bob Albright, a 67-year-old X-ray repairman from Kimberton who woke up at 4:30 a.m. to load his pickup truck with 40 different plants for competition. He hauled an enormous cactus, thought to be at least 25  years old, on a hand truck. Zale accepted it -- but only after Albright removed rocky debris scattered among the cactus' spines using a pair of foot-long tweezers.

Nearby, Don Slater, chairman of the competitive class committee, and Kristine Qualls, the vice chair, monitored the action. They had spent the last few days trying to avert minor disasters: The wooden platforms that had been provided for container-garden entries had sides but no tops. And the patio garden beds were still being constructed when the exhibitors arrived to decorate them.

And, they are already thinking ahead to next year. This week, they held a preview meeting to recruit for 2018 and to distribute applications to prospective exhibitors.

"It used to be you had to drop it in the post that day or you wouldn't get in," Qualls said. "I wish I could say that was the case now."

But there are more immediate problems: coordinating categorizing, tagging, judging, displaying and watering all those plants, and shuffling mountains of paperwork. (They have discussed digitizing the judging process, but they're not there yet. Even digitizing registration was controversial among the less technically inclined exhibitors.)

And, perhaps most important at the Philadelphia Flower Show, they are the last line of defense against horticultural faux pas.

Often, they find plants that are not labeled correctly. Other times, the mortifying moments are even more subtle, apparent only to knowledgeable gardeners.

"We had a case last year of black-eyed Susan and witch hazel planted together. Black-eyed Susan blooms in July, and witch hazel in January, so they look funny together," Qualls said. "But what can you do?"