The men’s and women’s qualifying rounds of the French Open started Monday, culminating a season of professional tennis on a surface that’s notoriously challenging to compete on: clay.

The court at Roland-Garros, the stadium where the French Open is held, is a five-layer sandwich of various stones and coal residue, topped off with a thin layer of red brick dust. The mixture can be unstable, as it can shift underfoot. By comparison, hard courts have a resin or acrylic top coat that provides an even surface. Grass has a rougher texture that gives the ball a lower bounce.

But any athlete who makes it to the French Open is “a phenomenal tennis player at that point” and learns to adapt to clay, said Steve Johnson, a retired tennis pro who has played in 10 French Open tournaments. NPR spoke with him and two players competing in this year’s French Open about how they have navigated the ruddy terrain over their careers.

Marta Kostyuk

As a junior player, Marta Kostyuk of Ukraine performed well on clay courts. She had more endurance, but she was also a lot more rigid in her approach to the game, she said, which didn’t bode as well once she advanced to the pros.

“I would set myself to play [a] certain way, and I basically wouldn’t change it,” she said.

So she’s had to learn to be more flexible. After all, clay is finicky. It shrinks and expands, so each step and bounce can feel different from another, she said.

Clay season is also short. It’s a series of tournaments that runs from late March to early June — a couple months out of the full season, which is mostly allocated to hard courts. So it can be hard to get into the groove, Kostyuk said.

It also doesn’t help that each clay court has its own DNA. For example, Madrid’s court is at a higher altitude, with thinner air that gives the ball less resistance.

“So the balls are just flying,” she said.

Her mother, Talina Beiko, played professionally and made sure Kostyuk practiced regularly on clay. The courts at Roland-Garros have a heavier consistency, like the ones she grew up playing on.

“It’s a very real clay court, the proper one for me,” Kostyuk said.

Kostyuk’s adaptability has paid off. In a span of three weeks, she won back-to-back clay tournaments in Madrid and Rouen, France, launching her from the 28th to the 15th best female singles player in the world on the Women’s Tennis Association’s ranking.

Steve Johnson

Red may be the clay of choice for several pro tournaments, but it’s not the only kind.

Red clay is more naturally available in Latin America and Europe than it is in the U.S., so clay courts in the U.S. often take on another consistency and hue, green.

“It’s a little bit more fine, it’s a little bit more slippery than the red clay,” Johnson, the retired pro, said. “So it gives you somewhat of the feeling that you’re on red clay, because you can move and slide, but the footing is not there.”

It can take players from the U.S., like Johnson, a little time to adjust to red clay. In Johnson’s earlier playing days, that could mean three or four tournaments. But with experience, that window dwindled to a week or two, he said.

“As a young pro, you sometimes feel as if you need to rethink the wheel a little bit based on the new surfaces that you play,” he said.

But playing on clay usually meant at least making a few tweaks to his technique, he said. Clay slows the ball down, which provides more time to respond to a shot. So Johnson might “wrongfoot” someone — going in a different direction than your opponent is expecting. He might play more aggressively, he said, or switch up his defense style.

Clay is also very sensitive to weather variations. The texture can be firmer on a gloomy, cool day, and looser on a hot day, Johnson said.

“It feels like you’re playing two completely different tournaments,” he said.

Hailey Baptiste

Hailey Baptiste is a 24-year-old American ranked the 25th best player in the world in women’s singles by the WTA. She also said it’s rare for young U.S. athletes to play on red clay courts. But there were two at the tennis club she practiced at in suburban Maryland when she was younger.

Not only did she get an early start with clay, but it’s her favorite surface.

“I really enjoy sliding around,” Baptiste says. “I feel like it’s easier, almost, because you can just kind of let your weight go when you stop, rather than having to take a ton of adjustment steps all the time on hard court.”

Baptiste said she has strong quadriceps, making it easier to control herself on slides, a crucial tool to stay balanced, slow down and reset on clay surfaces.

Last year, she made it to the fourth round of women’s singles at the French Open, and the first round of doubles. She’s up for doubles again this year.

She’ll likely talk strategy with her partner closer to the match, but she doesn’t plan on reinventing that wheel Johnson spoke of. Plus, she’s paired with someone who has dominated all types of courts — Venus Williams.

“Every time I play tournament, I’m playing to win the tournament,” Baptiste said.