Sneezy Landscapes?

June 5th, 2000

To gardeners, spring means enjoying beautiful blooms and sniffing sweet fragrances in the yard.

But to allergy sufferers, it means months of sneezing, red eyes, wheezing, popping decongestants and helping to raise stock prices in the Kleenex market.

It’s especially a problem for gardeners who have allergies — or allergy sufferers who garden.

There’s actually much that can be done to alleviate plant allergies other than years of immunotherapy shots or hiding out inside all summer, says California horticulturist Thomas Ogren, author of “Allergy-Free Gardening” (Ten Speed Press, $19.95 paperback, June 2000).

Ogren says the type and even sex of the plants in your very own landscape play a huge role in triggering hay fever, asthma, skin rashes and other allergic reactions.

“It’s not just ragweed blowing in from a field,” he says. “Landscaped urban areas produce their own heavy pollen loads… My point is it doesn’t make sense to plant highly allergenic plants in your yard if you have allergies.”

This strategy differs from what has been the conventional advice — that pollen blows so far and there’s so much of it around that it makes little difference what you’ve planted in your own yard.

Although Ogren agrees that some pollen can travel for miles, he says “the heaviest concentration of pollen from a tree is right around the drip line of the tree. When you get out 30 or 40 feet, you might find some but not a lot. Gravity cannot be defied.”

Ogren, a former nursery owner and dairy farmer, got interested in this topic when he was attempting to landscape his own yard.

“My wife has bad allergies, and I didn’t want to plant a landscape that would aggravate them. But there wasn’t much out there on it. No one seemed to know much. I was guessing. I went to horticulturists and botanists and they knew plants but not much about allergies. When I went to allergists, they knew allergies but didn’t know much about plants.”

So Ogren began reading everything he could find from around the world and quickly realized there are certain characteristics in plants that make them more or less prone to causing allergies.

“I have about 80 criteria now on factors that affect how allergenic a plant is,” says Ogren. “On no plant will all 80 appear, but there are a number of them that have 30 or 40 factors.”

Ogren also found there was no easy way for a typical non-botanist person who sneezes a lot to figure out exactly which plants are the most likely to cause trouble.

Using his 80 or so factors, Ogren devised a scale (called the “Ogren Plant-Allergy Scale”) that rates thousands of plants from 1 to 10. Plants rated low on the scale are least likely to cause allergies, while the 9s and 10s are the most common sneeze-makers.

A large part of his “Allergy-Free Gardening” book lists these ratings on an alphabetical, variety-by-variety basis.

Past books have attempted to zero in on “problem plants,” but they generally give broad advice, such as avoid maples, ash trees and wind-pollinated flowers.

Ogren says it’s not quite that simple.

For instance, he points out that the sex of a plant makes one of the most important differences.

“Most people don’t even realize plants have sexes,” Ogren says. “Some plants are male, some are female and some are bisexual.”

Male plants are much worse for allergy-causing because they produce the pollen that’s needed to produce fruit or seeds on the female plants. Females do not produce pollen.

“If you’ve planted a male red maple next to your patio, that thing in spring will be dropping pollen all over,” says Ogren. “The grains are so small that you don’t see them. But you’ll be breathing them and tracking them in the house.”

However, if the same tree were a female red maple, it would produce no pollen and have very little chance of triggering allergies.

One way to tell if a plant is male or female is if it produces fruits or berries. (Females are fruit and berry producers.)

Unfortunately, more and more of the trees and shrubs on the market are all males because consumers want “litter-free” plants that don’t drop “messy” fruits.

“While the males don’t produce fruits and seeds,” says Ogren, “they do produce vast amounts of irritating airborne pollen.”

He suggests that this increase in “male landscaping” is at least partly to blame for the increases we’re seeing in hay fever and asthma.

Sometimes the plant labels and plant names give a clue as to the sex of the plant, but most often even nursery personnel will not be able to tell you if a particular, say, yew bush is male or female.

That’s where Ogren’s book comes in — he names exact varieties that are all-male or all-female.

How the flowers on a plant are constructed also make a big difference in allergic reactions.

Plants with pollen on the end of exposed anthers (the thin, protruding male part of a flower) are usually plants that depend on wind for pollination. Those are more likely to cause allergies.

However, flowers with anthers recessed within the flower are usually insect-pollinated and less likely to cause airborne pollen problems.

“Snapdragons are a good example,” says Ogren. “These are usually pollinated by bees. A bee has to push down the lower lip of the flower to get in at the pollen. When the bee backs out, the bloom snaps shut without releasing pollen into the air. It isn’t hard to see why the snapdragon rates as one of the best flowers for an allergy-free garden.”

Among the other factors Ogren used to rate plants’ allergy-producing potential:

* The size and weight of the pollen. Bigger, heavier grains fall out of the air faster and cause less trouble farther from the source.

* How long the plant produces pollen. Some plants produce pollen for only a week out of the whole year. Others produce pollen over several months, which causes a longer period of trouble for sensitive persons.

* Fragrance. Some plants produce volatile oils that are behind both the fragrance and the allergic reactions that some people have. In other words, pollen is not always the culprit.

* The dryness of the pollen. Dry pollen floats a greater distance and sticks more readily to mucous membranes.

If you’ve got an allergy problem, Ogren advises that it might help considerably to identify the plants nearest you that are causing reactions and consider removing them.

If you don’t know which ones you’re allergic to, he suggests starting with the plants in your landscape that are rated 9s and 10s in his book. (If you don’t even know the names of the plants, he suggests taking samples to a garden center for identification.)

“If you have a yard that overall is ranked in the 2 to 5 range, you’ll have very little problem,” Ogren says. “But if you’re up around 9 or 10, these are the ones that blow you away… Sometimes it might be just one tree or a single row of shrubs that’s causing most of the problem.”

SIDEBAR 1

Plants are behind a significant number of the 35 million Americans who have chronic sinus problems, the 14 million who have asthma and the 50 million who suffer from hay fever.

Some tips on reducing allergic reactions to plants and lawns:

* Remove heavy pollen producers from your yard and choose only low-allergy plants when planting new plants. See “Allergy-Free Gardening” by Thomas Ogren (Ten Speed Press, $19.95 paperback, 2000) for plant-by-plant ratings or visit the www.allergyfree-gardening.com Web site.

* Wear a mask to filter pollen when cutting grass or working outside.

* Try to do your outside work in the middle of the day when pollen counts are normally at their lowest.

* Heavily prune flowering trees and shrubs just before they bloom to stop pollen release. This will take away the beauty of the flowering, but it’ll also take away a key source of hay fever and asthma.

* Cut grass later in the day since most grasses release most of their pollen between 3 a.m. and 8 a.m. Or consider replacing lawn with low-allergy groundcovers such as ajuga, barrenwort, candytuft, creeping sedum, sweet woodruff, vinca or wintergreen.

* Shower after coming inside and wash your clothes to remove any pollen brought inside.

* Don’t hang wet clothes outside to dry overnight or early in the morning. This is when they’re most likely to become covered with grass pollen, which then is brought inside.

* If you take allergy medications, take them before going outside to work in the yard.

(Sources: Asthma and Allergy Foundation of America and “Allergy-Free Gardening” by Thomas Ogren.)

SIDEBAR 2

Some of the best and worst plants for respiratory and skin allergies, according to the Ogren Plant-Allergy Scale in Thomas Ogren’s new “Allergy-Free Gardening” book:

* Least Likely to Cause Trouble

Ajuga

Ash (females only)

Balloon flowers (Platycodon)

Baptisia

Barrenwort (Epimedium)

Bayberry (female)

Bear’s breeches (Acanthus mollis)

Bellflowers (Campanula)

Bergenia

Blackberry lily

Blue atlas cedar

Blueberries

Cactus

Coleus

Columbine (Aquilegia)

Candytuft

Coralbells (Heuchera)

Elephant ears

Firs

Forget-me-nots (Myosotis)

Foxglove

Fringetree (female)

Gaura

Germander

Geum

Ginger (Asarum)

Gingko (female)

Grape hyacinths

Hemlock

Holly (female)

Hollyhocks

Impatiens

Jacob’s ladder (Polemonium)

Juniper (female)

Jupiter’s beard (Centranthus ruber)

Kerria

Kiwi vine (female only)

Larch

Lobelia

Oregon grape holly

Peony

Penstemon

Petunias

Plectranthus (Swedish ivy)

Purple rock cress (Aubrieta)

Maple ‘Indian Summer,’ ‘Autumn Glory,’ ‘Bowhall,’ ‘Red Sunset,’ ‘October Glory’

Nandina

Nemophila

Nierembergia

Orchids

Poplar (female)

Portulaca

Pulmonaria

Red chokeberry

Rock cress (Arabis)

Salvia

Sea pinks (Armeria)

Sedum

Silver maple (female)

Snapdragons

Solomon’s seal (Polygonatum)

Sourwood

Sweet woodruff

Veronica

Vinca

Water lilies

Willows (female)

Wintergreen (Gaultheria)

Yucca

* Most Likely to Cause Trouble

Artemisia

Ash (white and black types)

Bayberry (male)

Boxelder (male) ‘Aureo Marginatum’ or ‘Baron’

Blue fescue

Castor bean

Fountaingrass (Pennisetum)

Fringetree (male)

Goats beard (Aruncus)

Japanese cedar (Cryptomeria)

Juniper (male)

Meadow rue (Thalictrum)

Oaks

Pearly everlasting (Anaphalis)

Poplar (male)

Sedge grass (Carex)

Silver maple (male)

Sneezeweed (Helenium)

Stevia

Sycamore

Willow (male)

Yellowwood

Zelkova