All roses look pretty, but not all roses smell pretty. Any schmuck can admire the petals, but those who want to enjoy the sweet smell have to be a little more strategic about things.

Portland is the City of Roses because of its weather: mild, damp winters and warm but not hot summers. From that, a garden has bloomed, including the Rose Festival wrapping up this week, and the International Rose Test Garden.

WW sat down with Harry Landers, curator at the International Rose Test Garden, and we read the smelling notes of John Clements, the late owner of Heirloom Rose Nursery in St. Paul, east of McMinnville, who operated the largest family-owned rose nursery in the United States, to learn  how to more fully appreciate the ubiquitous blooms. Here are a few things you probably didn't know.

Smell early. The best time to sniff is in the morning, when the temperature is between 65 and 70 degrees, according to an article written by Clements. "As the day gets warmer, the fragrance oils evaporate," he writes. Roses also smell differently depending on the time of day. "It's more intense when the sun warms the petals," Landers says. "Some roses are fragrant no matter what—even when it's 40 degrees you can still smell them. But for the most part, you can smell one rose, come back a half-hour later and can't smell anything out of that same rose."

Don't expect every rose to smell. Roses vary widely in their scent, many having almost none at all. That's because rose breeders gave up on smell during the era of polyester and disco, when people wanted disease-resistant roses that didn't require chemical sprays. Unfortunately, that led to breeding scentless roses. "They could not with the technology then split the genes between the fragrance and the disease resistance, so they gave up the fragrance, and that was a big loss," Landers says. Legendary British breeder David C.H. Austin is credited with reviving strongly scented roses.

Know your nose. Noses, like tongues, have different sensitivities. "Some people have a much keener sense of smell than others, so a rose may smell strongly scented to one person and not another," wrote Clements. "Each person is subjective when it comes to rose fragrance." Clements said a rose breeder he knew, oddly, couldn't smell yellow roses.

Sniff for the unexpected. Typical rose scents include vanilla, myrrh, raspberry and citrus, according to Landers. According to Clements, you may also be able to smell apricot, tobacco, cedar and baby powder.

There are professional rose smellers. "A lot of the breeders actually have 'professional noses' come in, like those who smell perfumes or taste wines," Landers says. "They can pick up the blackberry or vanilla or myrrh scents." These are the people who write the descriptions that accompany roses when you visit a nursery or buy them from a rose breeder.

Smell is competitive. The International Rose Test Garden hosts the annual Portland's Best Rose contest, led by the Portland Rose Society. Categories include best fragrance, which this year went to the Sugar Moon Hybrid Tea Rose.

The Michael Jordan of scented roses is the Double Delight Hybrid Tea Rose. Voted "best fragrance" in 1977 by the All-America Rose Selections, its "sweet, spicy" scent remains the top-rated fragrance rose of all time. At the International Rose Test Garden, look for it in the center plot farthest from the parking lot. 

GO: International Rose Test Garden, 850 SW Rose Garden Way, 227-7033. 9 am-7 pm daily all summer. Free.