If there is such a thing as a "mad gardener," William Radler, inventor of the wildly popular Knock Out Rose, might qualify. Radler, who was director of the Boerner Botanical Gardens in Hales Corners from 1981 to his retirement in 1994, is known as "Mr. Knock Out" in the gardening community. But the nickname might also have been coined by any visitor to his personal garden on the grounds of his stately home in Greenfield.

Radler’s lifelong interest in rose gardening began as a boy, where he found the colorful Jackson & Perkins catalog in the living room of his grandfather’s small house on the banks of the Milwaukee River. The images of beautiful and bright blooms enchanted Radler in a world where children were to be seen and not heard.

"As I paged through the catalog, I envisioned having some roses of my own," Radler says.

He eventually planted about 150 roses in his parents’ small yard, and went on to earn a degree in landscape architecture at UW-Madison, where he also studied fine arts.

Today, Radler’s 2-acre garden features 1,500 roses, all grown from seed. Named after a German garden said to have the largest collection of roses in the world, Radler’s "Rosarium" is designed to produce breathtaking vistas from every angle. The Knock Out Rose, introduced in 2000, is just one of its stars.

"The Knock Out is the world’s record top-selling rose of all time. It was the right plant at the right time," Radler explains.

The Knock Out is technically classified as a shrub rose, but Radler prefers to call it a landscape rose. It is a multistemmed, woody plant that is winter hardy and resistant to the diseases that often plague other rose varieties. With four "blushing" cycles during the growing season, the Knock Out is also a prolific bloomer.

Radler’s company, Rose Innovations, now has six full-time employees and more than 20 rose varieties on the market. He names each new rose he develops, including Winner’s Circle and Morning Magic. One of his favorites, the Cancan Climber, is distinguished by a succession of magenta, pink and cream on its petals ­— reminding him of the swirling skirts of French dancers.

Radler’s Rosarium is a wonderland, not just for rose enthusiasts but for anyone who appreciates natural beauty. And it is always evolving. Specimen plants include his collection of unusual evergreens and conifers, such as a Japanese Umbrella Pine and Weeping White Pine.

"I love fragrant plants," he says, so in early spring visitors will find red tulips that are scented like oranges, and bright yellow sedum that changes colors with the seasons. "That’s part of the excitement," he says. A bog garden and a "Weird Plant" garden also add interest. Each of Radler’s thousands of plants are carefully labeled and catalogued.

Radler grew his silver maple tree from seed. He says he prefers to start small and nurture a plant to maturity.

"It’s all part of the magic of life," he says.

Radler enlisted the services of Dave and Heather Schuster at Terra-Firma Landscape to interpret his ideas for the garden’s structural features. A rock-bottomed creek meanders throughout the space, punctuated with charming bridges and waterfalls. A series of stereo speakers ensures music can enhance the experience. The focal point, however, is a towering 40-foot obelisk, surrounded by a stand of sugar maples. Radler says the structure was originally built for the Frank Lloyd Wright exhibit at the Milwaukee Art Museum.

The latest addition is Golden Pond, stocked with large goldfish in shimmering shades of red, white and blue. A shell-shaped outdoor shower, built of stone, is placed nearby. It comes in handy after a day of working the soil.

Not content just to raise plants, Radler is now breeding tropical fish in 12 aquariums. He points to his prize collection of bright yellow goldfish, which originated in Asia. They are rare, he says, because "yellow was the Emperor’s color" and not readily available to the masses.

Radler says he wants the Rosarium to delight visitors for decades to come. At some point, he says, he hopes it could be used for rentals or fundraisers for his favorite causes.

"I’m really a very practical person," Radler insists, but his garden, and his work, reflect an imagination without limits. m