Mariners Roll Out Green Carpet -- Safeco Field's Grass System Is Pure Science

Horticulture. The mechanics of keeping the grass green at Safeco Field.

A field grew in Olympia: about four acres of Kentucky bluegrass mixed with perennial ryegrass, which is about to carpet the new home of the Seattle Mariners.

Through tomorrow, the sod, rolled up like giant paper towels, is being transported to Safeco Field, where it will be pampered in technologically advanced ways not only to fool Mother Nature but to withstand major-league-baseball cleats.

Turf grass, specifically growing it, can be explained by Hank Wilkinson, a professor of turf-grass science at the University of Illinois. He's the man baseball groundskeeping experts turn to when choosing new turf, and he is working as a consultant for the Mariners.

"The first thing to understand," Wilkinson said, "is that a baseball field is not a natural situation."

The environment is contained by stadium walls, and those walls - or an 8.9-acre roof like the one at Safeco Field - limit the amount of sunlight coming in. Then there's all that mowing.

To keep players injury-free, to keep the ball moving fast and to look nice, baseball fields are cut short, typically to the height of an inch. Mowing, which makes the grass tougher and more dense, may occur twice on game days.

Irrigation is another issue. A baseball field cannot stay wet long; it has to be dry for games. Growing the grass in a porous medium, or using something to extract the water, can help grass and roots dry faster.

Safeco Field will have both.

The grass covering the 106,000-square-foot field will grow in sand - 5,000 tons of it. Under that runs 1.5 miles of pipe and 22.5 miles of plastic hose. The pipes drain and oxygenate; the hoses heat.

The $150,000 SubAir drainage system was invented seven years ago by the superintendent at the Augusta National Golf Club. The St. Louis Cardinals bought the first SubAir system in 1996 when Busch Stadium converted from artificial to natural turf. The Seattle Seahawks plan to install it in their new stadium, too.

Underneath the sand at Safeco Field, buried in 2,000 tons of pea gravel, are the drain pipes. They are attached to a 200-horsepower pump that sits in a room behind right center field. The pipes are capable of draining 130,000 gallons of water within minutes, proved recently in a drainage test, according to Steve Peeler, the Mariners' head groundskeeper.

"Drainage won't even be a problem," Peeler said.

A wet Safeco Field, soaked with 2.5 inches of water in one hour, would be ready for play in 45 minutes, team officials say. Because of the retractable roof, such a drenching is unlikely, but the numbers make a point.

The SubAir system also sucks oxygen from the atmosphere through the turf, into the dirt and the 10-inch-deep root zone.

The ideal level of oxygen in the soil would equal the amount humans breathe in the atmosphere, Wilkinson said. The SubAir system, which will be used for about three hours every three days, will oxygenate the soil to this optimal level.

SubAir is the plant equivalent of a human oxygen bar, or, as Peeler put it, "It's the best thing invented for turf since automatic irrigation."

The irrigation system at Safeco Field will involve about 75 sprinkler heads in 16 zones throughout the field. Each zone has its own sensors to indicate the amount of water needed at any given time. The field will require about 40,000 gallons of filtered water (including reclaimed rainwater) a day.

"You wet it and dry it. That makes happy grass," Wilkinson said.

So does fertilizing.

The field will be fertilized every week with chemical fertilizer. Organic fertilizers won't be used, Peeler said, because they are incompatible with sand.

The big trick, however, is battling the Puget Sound climate, especially the lack of warm, sunny days.

Ultraviolet rays are present even on cloudy days, which is why officials will strive to keep the stadium's retractable roof open as often as possible. But it is the sun's warmth that helps plants grow, especially in the spring, when they need to be nudged from their dormant winter state.

To compensate for the low levels of direct sunlight, coiled hoses buried 10 inches deep in six different areas of the field will heat the field's surface temperature to about 55 degrees.

"Baseball season goes into the fall, when grass normally slows down growing. We may need a field sometimes through November," Wilkinson said. "And in spring, in early April, when we need it green, it might not be warm enough."

Country Green Turf Farm of Olympia has been growing the Mariners' grass for a year. The grass chosen by Wilkinson is a combination of three blends of Kentucky bluegrass and two blends of perennial ryegrass. That adds up to an 80 percent bluegrass-20 percent ryegrass mix.

That blend is different from the grass that typically borders homes in the Puget Sound area, and in fact has raised a bit of controversy among some people who suspect it won't hold up.

Experts usually recommend a blend of perennial ryegrass and fescues for the region's cloudy climate. That mixture, said Eric Miltner, an associate professor in crop and soil at Washington State University, also is "competitive" and helps keep other types of grass at bay.

But the game of baseball, not the Northwest climate, was paramount to Wilkinson when choosing the Mariners' grass.

"It's not what would look the best or what would grow the best, but what plays the best," Wilkinson said.

Ryegrass alone, Wilkinson said, is a poor choice for baseball because its blades are waxy. They get slippery when wet, and even the SubAir system wouldn't be able to dry them thoroughly.

What makes bluegrass suitable for baseball are its rhizomes. These stems don't go straight down, they veer horizontally, shooting up more plants and setting down more roots. It's a webbing of sorts that makes bluegrass strong as well as cushiony for the cleated foot, Wilkinson said.

Bluegrass is a higher-maintenance grass, taking 14 days to establish itself from seed compared with three days for ryegrass. But a baseball field, Wilkinson argued, is maintained to a degree far and above the typical homeowner's lawn. And for this first season at Safeco Field, the ryegrass will serve to strengthen the bluegrass as it fully establishes itself.

Bluegrass, the more competitive grass, eventually will take over the field.

Still, to be certain they made the right choice, Wilkinson and others from the University of Illinois studied bluegrass growth in Seattle, collecting data over the past six years. The chosen blend was grown in six miniature stadiums set up at the turf farm. The effects of wind, rain and sun were measured on what would end up as right, center and left fields.

"What we collected shows it grows tremendously," Wilkinson said.

A 3-foot chunk of sod plucked from the turf farm also has been growing at Safeco Field for the past six weeks. It was deliberately neglected: no water, no fertilizer, no SubAir. It was ripped out often and stomped back down.

The other day, Peeler fingered the turf, which was dry at the edges and slightly discolored. But its roots, looking like the tentacles of a jellyfish, were fibrous, long and white.

"No tender loving care, and it's doing fine," he said.

Florangela Davila's phone message number is 206-464-2916. Her e-mail address is: fdavila@seattletimes.com