First leaves pop open on barren trees. Then grass grows greener with each passing day. Blooms burst lemon-yellow on the forsythia as hyacinths, daffodils and tulips unfurl their Technicolor petals.
These are sights that lift a winter-weary heart, but may cause the nose to drip.
Now there’s a guide for planting flowers, shrubs and trees that won’t make you sneeze or wheeze — or maybe just not as much.
In “The Allergy-Fighting Garden” ($22.99, Ten Speed Press), author Thomas Ogren, a horticulturist who has spent decades studying plants and pollen, offers a guide for those among us who suffer from outdoor allergies.
He created a numeric rating system, called OPALS (Ogren plant allergy scale) for thousands of plants listed alphabetically by scientific name, genus first. They’re rated based on how allergenic they are. The worst plants for allergy-prone people get a 10 rating; the best, a score of 1.
“I’ve been gardening since I was 5 years old, seriously,” Ogren, 68,said by phone from his California home. “By the age of 7 or 8, I was trying to graft trees. I’ve been hybridizing my own roses for 40 years.”
Alhough Ogren doesn’t suffer from allergies, his wife, Yvonne, has both allergies and asthma. Years ago, he wanted to customize the landscaping outside their home in San Luis Obispo to make it allergy-proof for Yvonne. That’s when he discovered that there was very little research available about plants and allergies. Thus began a lifelong quest to discover the root of his wife’s struggles, and those of so many other allergy sufferers.
In his own studies, Ogren discovered that America’s zeal for mess-free landscaping also has led to an abundance of male trees and shrubs. The male plants don’t produce fruit, seeds or seedpods to make a mess in yards and gardens, but they do produce pollen, and lots of it.
Starting in the 1940s, Ogren said, the U.S. Department of Agriculture began to laud the properties of male trees, urging growers to use only males to take cuttings and use for grafting and clones. This continued through the ’60s and ’70s, and following the devastation of Dutch Elm disease, landscapers replaced dead elms mostly with other varieties of male trees.
“I stumbled on this, you can call it botanical sexism, or something like that,” he said. “For years, people laughed when I talked about this like I was exaggerating, but I could take pretty much anybody for a walk in pretty much any city, including Detroit, and show them — boom, boom boom,” he said. “I could take you to a retail nursery and show you what they’re selling. It’s almost all male trees.”
Ogren has begun advocating that cities adopt rules about planting female trees in their landscaping efforts, and has urged large commercial growers and nurseries around the world to adopt the OPALS system so people who come to purchase plants will know by looking at the label how allergenic they are.
His work is already having some impact. There’s now a pollen-control ordinance in Albuquerque, N.M., that prohibits the sale or planting of the most allergenic male trees and shrubs. Some limits also are in place in Las Vegas, Edmonton, Alberta, and Toronto.
But, Ogren said, everyday gardeners also can make a difference.
“What I always tell people is, ‘Deal with your own yard and get your own yard cleaned up as best as you can. Take the very worst stuff and replace it with the very best and then start fine-tuning it,’ ” he said.
The worst of the worst, he said, is a male yew, a popular, but poisonous, long-living evergreen. You can tell a male yew from a female based on whether it produces firm, waxy red berries. Those that produce berries are female. Those that don’t are male.
“I’ve like cured people, if there’s such a thing, by basically putting a chain saw to a male yew planted outside a bedroom window and put something else, something less allergenic, in its place, and boom! People start getting better,” he said. “There is no data on what getting poisoned every year from the pollen off a yew would do to you, but it isn’t good.”
The best choices: female varieties of yews, foxglove, cranesbill, female honey locust trees, hostas, blueberry bushes and fruit trees like apricot, apple, plum and pear. If they produce fruit, they are less likely to pose a big problem to allergy sufferers, he said.
“Any self-fruitful or self-pollinating fruit tree is not going to be an allergy problem,” he said.
As for annual plants, Ogren’s book gives excellent ratings to impatiens (1), snapdragons (1), veronica (2), dianthus (1-3, depending on the cultivar), petunias (2) and pansies (1).
Zinnias get a score of 3, and if you’re buying dahlias or begonias, the type you get really matters. The formal-double variety of dahlias gets an OPALS score of 2, but the singles get a score of 5. With begonias, generally those grown from a tuber get a score of 2, but those grown from seed have a 4 rating. But it gets even more complicated with begonias. Recently, nurseries have been selling an all-male variety called “Sparks Will Fly.” It is far more allergenic than any of the others, with an OPALS score of 7.
It’s hard to know when you’re shopping exactly what you’re getting, Ogren said. He suggests bringing his book with you to the nursery, so you know exactly which variety of each plant you should buy, and which to avoid.
“One of my ultimate aims is that all the nursery plants everywhere will be tagged with their allergy potential,” he said. “For the most part, it’s still tricky for people to go to a nursery and know what they’re buying.”
Ogren is on the board of directors for a nonprofit organization called the Society for Allergy Friendly Environmental (SAFE) Gardening, which is working to certify nurseries that have agreed to grow and sell female plants, and varieties of trees, shrubs and flowers that are low pollen producers.
“Times are changing, and I think horticulture needs to change with them,” he said.
“I’d like to see more consideration in landscaping. People say it’s a great book if you have allergies. I don’t have allergies myself, but it’s like, ‘How about you have consideration for other people?’ Why not be as considerate as we can?”
Tips for gardeners with allergies
The Allergy and Asthma Foundation of America has suggestions for other measures that people with allergies can take when gardening. Among them:
• Wear a facemask, hat, glasses, gloves and a long-sleeve shirt to reduce skin and nose contact with pollen.
• Ask a family member or friend who doesn’t have allergies to mow the lawn, and keep grass cut low — 2 inches high — to help keep stems of pollen from reaching too high into the wind.
• If you must have hedges (their branches collect dust, mold and pollen), keep them pruned and thin.
• Close the windows in the house while mowing and for a few hours afterward.
• Limit your gardening time to cool or cloudy days and in the later afternoon or evening when pollen concentration in the air is generally lower.
• Immediately shower and change your clothes when you go indoors and make sure to wash your hair to remove allergens trapped there.