Can Rays avoid retractable roof and still play on grass?

For true aficionados, baseball is not played on a glorified carpet.

From the bounce of the ball to the lack of grass stains on uniforms, artificial turf has yet to match Mother Nature as a playing surface for America’s national pastime.

After a flirtation with artificial turf in the 1970s, ’80s and early ’90s, that’s the conclusion Major League Baseball reached. Of baseball’s 30 teams, only the Tampa Bay Rays and the Toronto Blue Jays play on artificial turf and the Canadian team is set to switch to grass in 2018.

The Rays’ chance to convert would come with a new ballpark. But how do you let in sunlight to grow grass while excluding the heat, humidity and torrential downpours of a Florida summer?

The Miami Marlins solved the puzzle with an expensive retractable roof, part of the $639 million Marlins Park. Mindful of the cost, the Rays seem set on a different path and have said they want to explore technology like transparent roofs.

Maybe it’s a fixed roof and retractable walls, Rays President Brian Auld recently told a sports business gathering. We know we’d like to be able to grow grass.

Several major-league teams whose ballparks are topped by retractable roofs incorporated innovative stadium designs to ensure fields get more sunlight.

The roof at Miller Park in Milwaukee includes large panes of glass to let in light when the roof is closed. The Houston Astros’ Minute Maid Park has 50,000 square feet of glass running the length of the stadium’s west wall that lets in light and provides a view of the city’s downtown.

But a grass field under a permanent roof would be a first for Major League Baseball, other than an ill-fated attempt inside Houston’s Astrodome when it opened in 1965. The grass perished after sections of the translucent roof were painted white in response to player complaints about glare. That led to the development of AstroTurf.

Stadium technology has come a long way since then, making the growth of grass indoors more likely but still a challenge, industry experts say.

Two NFL stadiums under construction – U.S. Bank Stadium in Minnesota and the Mercedes-Benz Stadium in Atlanta – will have roofs made from ETFE, a film that lets in natural light.

The acronym is short for ethylene tetrafluoroethylene, a flexible polymer with qualities similar to Teflon. It is stronger than glass but lighter and cheaper.

Depending on what source you believe, the plastic film was developed either for the space industry or the horticultural industry, where it is used for greenhouses.

Not in dispute is that the film admits 90 to 95 percent of available sunlight, including ultraviolet light needed for grass to grow, said Michele Roth, business development manager with Birdair, a New York-area manufacturer that built the roof for Tropicana Field and is fabricating ETFE roofing sections for the Mercedes-Benz Stadium.

It’s been very popular in Asia and Europe for all that time, Roth said. In the last 10 years, maybe even less, it’s been catching on and trending here.

The roof uses compressed air between two layers of ETFE film to give it structural integrity. The film can be dotted with pigments to cut down on solar gains from direct sunshine, Roth said.

For the new Vikings stadium, the transparent roof is intended to help avoid the dark, claustrophobic feeling of an indoor stadium. It will include five pivoting doors to let in more sunlight and fresh air.

They want the ability to feel you’re outside yet you’re protected, Roth said. Still, neither of those stadiums will feature natural grass indoors, a combination that can be found in Dunedin. That’s Dunedin, New Zealand. Forsyth Barr Stadium was built in 2011 for the upcoming Rugby World Cup. It is the work of renowned sports architectural firm Populous, which describes it as the first permanently covered stadium with natural grass. For fans seated inside the stadium, clouds and a nearby mountain are clearly visible through the roof.

About 3 percent of the stadium’s field is artificial strands of grass to help it endure wear and tear from athletes.

But it has had problems.

The cost of maintaining the field at the $130 million venue led Dunedin, which owns the complex, to consider replacing the grass with turf, according to the Otago Daily Times.

That is to be expected, said John Trey Rogers, a Michigan State professor who specializes in turf grass science.

Rogers said the only chance for a grass field at an indoor stadium is for designers to keep it foremost in their plans, orienting the stadium footprint and incorporating other design features to get the maximum amount of sunlight onto the playing surface.

Professional sports teams already augment sunshine with grow lamps. Even without roofs, stadiums like Lambeau Field in Green Bay, Wisconsin, rely on lamps, particularly during winter. Increasingly, growers and groundskeepers are turning to blankets with LED growth lights embedded.

Another solution came from the designers of the University of Phoenix Stadium in Glendale, Arizona, home to the Cardinals of the NFL. The stadium features a retractable floor, which slowly slides outside the stadium so the field can bask in the Arizona sunlight.

The turf industry has also tried to develop shade-tolerant grass for stadiums but with little success, Rogers said.

A grass field typically needs six hours of sunlight per day, Rogers said. That’s easy to achieve in June, but not so easy in December.

Those are the issues that will face the Rays if the team wants to avoid re-creating the sterile Trop environment in its new ballpark.

I don’t care how good the roof is, there will be some shade issues in certain parts of the field, Rogers said. We have grasses that can survive in shade but we do not have grasses that thrive in shade. Thriving means being able to recover from 200- to 300-pound linemen beating on each other.–