Gardening: Before planting, brush up on allergy details

Nancy Szerlag
Special to The Detroit News

If you’re in the market for a new tree or shrubs this spring, and allergies and asthma are issues for those who live in your house, Thomas Ogren’s book “The Allergy Fighting Garden” (Ten Speed Press) is a must read. It explains what you need to know to choose the right plants to develop a garden and landscape that can be enjoyed by all throughout the season.

Ogren’s method for combating allergy and asthma triggering allergens is based on the fact that it’s the male plants that produce pollen. He’s painstakingly researched thousands of plants and ranked them according to a simple system he devised called the Ogren Plant Allergy Scale (OPALS), which as been adopted for use by the United States Department of Agriculture.

Ogren’s book includes more than 3,000 plant listings, each ranked according to the OPALS scale of 1 to 10 — 1 being allergy-free and 10 the worst offenders. Small icons — stars for winners and the universal ‘No’ symbol, a circle with a slash — make for quick referencing.

Ogren’s pollen calendar lists approximate periods of bloom for the most commonly used allergenic plants that’s worth its weight in gold for allergy sufferers.

A listing of useful allergy-based websites is also worth perusing.

Ogren also includes notes about other allergic reactions plants may trigger, as well as cultural information.

Unfortunately, the plants are listed alphabetically by their Latin names, followed by their common names. The common names of plants are not indexed, so a plant encyclopedia indexed by common names, either hardbound or online will be a big help.

Ogren explains, “Today there’s an overabundance of male varieties of trees and shrubs that produce lots of pollen and rate 9 to 10 on the OPALS scale, because homeowners don’t want the female plants that bear fruit and seeds that make messes.” But, where available, he gives names of both female and male varieties to make your plant search easier. Take the red maple (Acer rubrum) for instance. Red maple (A. rubrum) ‘Autumn Spire’ is a male with an OPAL ranking of 9 — a real pollen pumper, and garners a ‘NO’, as in do not plant, symbol from Ogren. However, A. rubrum ‘October Glory’ is a female that ranks 1 on the OPALS scale and it gets a star for zero pollen.

If you have a big Taxus Yew planted outside your bedroom window and a runny nose keeps you awake in spring you might have a male plant — a 10 on the OPALS scale, that needs replacing.

Nancy Szerlag is a master gardener and a Metro Detroit freelance writer. Her column appears Fridays in Homestyle. To ask her a question go to and click on Ask Nancy. You can also read her previous columns at