The art and science of roses

Tom Carruth, hybridizer at Weeks Roses in the Pomona, Calif., research facility, has kept some pretty famous company — Marilyn Monroe, Julia Child, Barbra Streisand, George Burns. But he’s more apt to walk the rows of the greenhouse instead of the red carpet. These famous names are a smidgen of the profuse amount of roses Carruth has hybridized over the years. Many of his selections have become All-America Rose Selections (AARS) winners.

The combination of art and science drew him to rose breeding. The scientific part of rose breeding is a meticulous process — one that sometimes takes more than a decade.

The process begins in winter when Carruth and his assistant, Christian Bedard, select about 150 parents and determine roughly 1,000 crosses for the year. In the spring, potted parent plants are moved inside the greenhouse — some named varieties and some test varieties. All plants are painstakingly labeled with a name and assigned a pollen number. After four to six weeks of growth, the plants will produce their first flowers.

About 24 hours before the pollination, most of the petals are removed and all of the anthers are cut off with a small knife. The anthers are retained and allowed to dry overnight, which releases the pollen grains. The anthers and dust-like pollen are transferred to small jars. The next day, the plants are ready for pollination. Camelhair brushes are used to collect the pollen, and the pollen grains are gently applied to the stigma. Each flower is tagged with the pollen number of the father. The pollinating season lasts from April to mid-July.

About 3 weeks after pollination a young rose hip appears. Harvest lasts from late August until the end of September. During harvest, the hips from any one female are kept carefully separated by the different pollen parents.

Seeds are removed from the hip in a slurry of water by using a blender, and the slurry is washed through several screens. The seeds are then stratified for about six weeks. Seeds are planted in raised beds. From the 850 or more crosses, more than 200,000 seeds are planted on average each year.

After about four to six weeks growth, evaluation begins. From 200,000 seeds, only 800-1,000 will be selected the first year. In July and August the seedlings are grafted onto rootstock in the field. The budded seedlings are observed twice a week during the flowering season for flowering capacity, fragrance, disease resistance, vigor and habit.

After three to five years of further evaluation, only 10-12 go on to AARS trials. After two years in AARS trials, three of four varieties make it to the trade, some suprisingly. “The cross that produced Betty Boop wasn’t particularly exciting on paper,” he said. “Yet it produced what would become a primary bloodline for our work.”