Select the right plants to reduce allergies in the garden
Does garden work make you sick? Literally? Or is there someone else in your life who can’t breathe freely in the presence of plants and other garden materials? If so, give yourself or that other a break. Change your plant choices, planting arrangements and work habits now to reduce your garden’s allergy irritation quotient.
A sizable portion of the U.S. population suffers from allergies. Many of the afflicted are children, but adults are learning, to their surprise, that these conditions can develop even late in life. To some of these sufferers, their allergies are only low-level nuisances. Others face more serious symptoms. Every one pays some cost and makes compromises to get by.
Spot allergy offenders before they’re under your nose
The word pollen comes from the Latin for “dust.” When it’s airborne, pollen can be a potent allergen. However, not all plants produce pollen and not all pollen floats in air. People with hay fever are wise to look for pollen-free flowers and heavy-pollen plants.
Pollen-free flowers are not common. Pollen is essential for seed formation, so in the natural course of things, every plant species produces these yellow, orange, or other-colored grains on stamens—the “male” portion of a flower. The important thing here is that in some species such as holly, mulberry, kiwi and ginkgo, some individuals in the group make flowers without stamens. These “females” are the seed-bearers of their species, and they are ladies a person with allergies can appreciate. (See sidebar with female and male plant lists: “Battle of the sexes.”)
Wind-pollinated means trouble
The worst kind of pollen is from wind-pollinated plants—”anemophilous” species. Such grains float so they’re easily inhaled, plus the species that produce them tend to go overboard when it comes to amount. Less troublesome is sticky and heavy pollen, produced by plants that rely on insects and birds to carry it around. These heavy pollen “entomophilous” plants also make less pollen than wind-pollinated species. They don’t need clouds of the stuff when they can rely on hungry pollinators to race directly from one flower to the next.
There are several ways to distinguish between wind-pollinated and heavy pollen plants. One is to check lists such as the sidebar in this article: “Most common culprits in pollen allergies.” Another is the shake test. A third involves learning to recognize what bugs and birds find attractive.
The shake test is simple. Shake plants to see where pollen clouds form. Ask someone who does not have pollen allergies to walk your yard every week or two from early April through late June—the months when pollen counts from trees and shrubs are highest—and rattle your plants. Where this raises puffs or clouds of “dust,” you should doubt that plant. Is it one you are allergic to, or a close relative? Is it one many people are allergic to? You might want to replace such a plant with something more innocuous.
Trees, grasses and weeds most to blame for allergies
When doing shake tests, don’t focus on plants with obvious bloom. The plants most often responsible for pollen allergies—certain trees, grasses and wind-pollinated weed species—have flowers so inconspicuous or so different from typical florist flowers that we may think they have no bloom at all. Where birches or pines overhang a patio and coat it with pollen, people who live there often fail to connect plant to powder. Gardeners who bump branches while clipping juniper bushes in spring are often shocked by the puffs of yellow pollen this stirs.
Not all airborne pollen is problematic, and some is much worse than others. Knowing which to look into is a big first step.
The third way to recognize airborne and heavy pollen involves looking at pollinators, flower sizes and form. If you see that many bees or other flying insects visit a particular kind of flower, chances are good that the only way that plant’s pollen moves is on the legs and body of a carrier. Even before you see insects, if you keep in mind that they follow visual clues in looking for food you’ll start to recognize the plants they service—those with big blooms or many small blooms in showy, large clusters.
Some people are allergic to bee stings, and might want to focus on bird- and butterfly-pollinated plants. These generally have flowers shaped like or equipped with deep, narrow funnels where nectar collects as the blooms ripen.
Spotting and reducing non-plant allergens
Although fewer people are allergic to molds and fungal spores than to pollen, these can trigger allergic reactions too. They rise up by the millions every time you rake leaves, turn the compost or disturb a mulch layer.
So hire a helper to rake leaves, or wear a mask when you do that chore. Work on a cool, still day after a rain, when the air is less likely to carry allergens. Let your city or township compost your leaf litter and other yard waste—don’t pile it and mix it in your own yard.
Eliminate or reduce your use of organic mulch such as bark. Switch to gravel mulch, which allows spores, mold particles, and dust to fall down into the spaces between stones. That’s better than having it rest at the surface where it can take off in the breeze that also caresses your window.
Organic matter tends to build up in stone mulch over time, so its ability to absorb troublesome particles decreases over time. Sprinklers splashing on its surface can raise the settled particles, too, so consider trickle irrigation or weeper hoses.
Also, weed seeds settle into that organic build-up, and can be difficult to eradicate without the use of herbicides that you probably should avoid. So plan to replace stone regularly.
If periodic removal and replacement of gravel is beyond your budget, try a triple thickness of newspaper as mulch, held in place with a thin layer of Turface or another of the gravel-like soil conditioners. When such products become gummed up with organics, they can be covered with a new layer of paper and clean Turface. The original layer will mix gradually, harmlessly into the soil.
Replace troublemakers with low-allergen plants and materials
When you remove troublemaking pollen producers, replace them with species that produce less pollen and are pollinated by insects or birds. Double-flowered varieties are often good choices, since what’s been lost in developing those extra petals on a double rose of Sharon (Hibiscus syriacus) or snowball viburnum (V. opulus ‘Roseum’) are the pollen-producing stamens.
Be sure to learn the mature size of each new plant you consider, and place your additions where they can grow without pruning. Pruning is a branch-rustling, mold-raising chore that allergy sufferers should bypass.
Design more dramatically, and build in filters
Two more things to aim for as you place new plants are high contrast and massed effect, so that you can enjoy your landscape even from afar or through glass. Try clumps of red foliage plants near yellow, big-leaf plants in front of lacy leaf or needled species, distinctly shorter items at the feet of taller individuals, and combinations of varieties with distinctive, no-prune shapes.
Focusing on the distance may help you free up the foreground too. Take vines and shrubs away from your windows where they have a greater potential to contaminate your air.
Whenever you can, place windbreaks between yourself and problem plants upwind in your neighborhood that you can’t eliminate. This calls for using binoculars or imposing a little on neighbors as you do more shake tests to identify the plants that may be causing you trouble. The potential pay-off makes it worthwhile. You don’t have to account for the whole neighborhood—tree pollen can carry a long way but most falls within about 50 feet of the source.
Hedges and fences can serve as windbreaks, slowing wind speed on their lee side for at least ten times their own height. Place a windbreak so that it is at least five feet upwind of any place where you plan to sit or work, because the space just downwind of a hedge receives fall-out as the wind slows and is forced to drop its load of particulate matter and pollen.
Reduce your work to reduce your exposure
Do all you can to reduce your yard work. Throw a garden party twice a year and invite sympathetic friends to help. Have all the materials lined up and ready, and bring your hired help in that same day.
Mowing spells allergy trouble, so hire that chore out, and replace lawn where you can with no-mow groundcovers. Have the lawn aerated and treated annually with slow-release fertilizer in the cool, still days of late fall so that turf will be fuller and healthier, less likely to harbor weeds such as ragweed.
Choose plants that are well suited for your site, and not susceptible to pests so that they will be healthy without application of fertilizers, herbicides and pesticides. All of these products are potential trouble for people who have already developed sensitivity to pollen, mold or dust.
Work smart when you spend time in the garden
Finally, decrease your risk by working on cool, windless days, and after every air-cleansing rain. Avoid warm, dry, windy days when pollen counts are highest.
While you’re out, cover your arms, legs and neck. Wear a mask if you mow or rake. When you finish working, undress in the garage and leave work clothes and shoes outdoors—one gram of soil may contain thousands of pollen grains. Shower after working, so you won’t transfer pollen grains, mold or spores into your clean clothes or bed. We can love our plants without sleeping with them!
Most common culprits in pollen allergies
Of 250,000 flowering plant species, only about 100 species have pollen that causes us trouble. Pollen allergy, also called hay fever, rose fever or allergic rhinitis, is most often caused by tree, grass and certain weed pollen. Here are some chief irritants, with the worst in bold.
Trees: alder, ash, aspen, birch, box elder, cottonwood (the pollen, not the fluff from female trees!), elm, hickory, juniper, linden, locust, maple, oak, poplar, sycamore, tamarisk, willow.
Grasses: Bermuda grass, bluegrass (Kentucky bluegrass), Johnson, orchard, redtop, sweet vernal, and Timothy grass.
Weeds: artemisias (including sweet Annie), clover (Melilotus species), cocklebur, curly dock (Rumex species), pigweed, plantain, ragweed.
Don’t count on numbers to gauge allergic impact
It’s not the number of pollen grains that causes trouble but their type and an individual person’s response to that type. A similar number of pollen grains—several million—may fall from one male pine cone or one dangling birch catkin, but fewer people react to pine pollen than to birch. An oak’s tassel-like flower may produce at only half the birch’s rate, and a grass plume releases just 1/20th of the pollen, but those grains have a major impact on the person whose body reacts to oak or grass.
Allergic to one, allergic to a group
When we react to pollen it’s actually a response to particular proteins on the surface of that pollen grain. A body allergic to a particular pollen protein often reacts to that protein in other, unrelated substances. For instance, birch pollen is a very common cause of hay fever. People allergic to birch often have food allergies involving hazelnut, almond, walnut and apple.
Recognizing wind-, insect- and bird-pollinated flowers
Wind-pollinated flowers give themselves away with their inconspicuousness and dangle. Most lack petals, which would interfere with the wind reaching the pollen grains. Most dangle from the plant’s top or upper branches, the better to be caught by a breeze.
Insect-pollinated plants tend to have visually attractive blooms—brightly colored, large or clustered. Pollinators such as bees, flies and butterflies home in on the ripe flower’s color and form. Wide petals or clustered flowers afford the insects a landing pad. Examples: apple (crabapple and other fruit trees), aster, daisy (and many of its relatives), mint (and many of its relatives), rose (and its family), tulip, and yarrow.
Hummingbird- and moth-pollinated flowers are tubular or have narrow nectar-collecting spurs at the bases of their petals. Many require a hovering approach. Bees can’t squeeze into the flower, their tongues won’t reach to the depth of the nectary, or they can’t hover long enough to sip their fill. Examples: beautybush (Kolkwitzia amabilis), butterfly bush (Buddleia), columbine, coral bells (Heuchera), fuchsia, hibiscus, horse chestnut (Aesculus), impatiens, lantana, salvia, trumpet vine, and weigela.
Battle of the sexes
Plants with separate sexes
Examine the plants below while they’re in bloom and you’ll find that the flowers on some never form pollen. A gardener with allergies might choose* those “female” forms and shun the pollen-making males.
- Ash tree
- Bayberry (Myrica pennsylvanica)
- Black gum tree (Nyssa sylvatica)
- Box elder
- Cork tree (Phellodendron amurensis)
- Fig trees (Ficus)
- Fringetree (Chionanthus virginicus)
- Ginkgo (Ginkgo biloba)
- Goatsbeard, perennials (Aruncus species)
- Juniper shrubs and trees (Juniperus species)
- Kiwi vine (Actinidia kolomikta)
- Mulberry trees
- Persimmon tree (Diospyros virginiana)
- Pistache tree (Pistacia chinensis)
- Populus species (cottonwood, poplar, quaking aspen, etc.)
- Red maple, silver maple
- Sumac shrubs and trees (Rhus species)
- Thalictrum species, perennials (meadow rue)
- Willow trees and shrubs
- Yew shrubs and trees
* Look for a sex-indicative variety name on garden center labels, or the presence of seeds or fruits (telltale of a female). If these signs are lacking, the only way to know the sex of the plant you are growing or considering buying is to inspect its blossoms for the presence or absence of pollen.
Some female, pollen-less varieties of separate-sex species:
- American bittersweet vine ‘Indian Maiden’
- Bayberry shrub ‘Myda’
- Corkscrew willow (Salix matsudana ‘Tortuosa’)
- Evergreen hollies such as “China Girl,’ ‘Blue Princess,’ and ‘Blue Maid’
- Junipers: Juniperus chinensis ‘San Jose,’ ‘Sea Green’; J. horizontalis ‘Blue Rug,’ ‘Grey Carpet’; J. sabina ‘Skandia’; J. virginiana ‘Blue Mountain,’ ‘Cupressifolia,’ ‘Emerald Sentinel’
- Kentucky coffeetree (Gymnocladus dioicus)
- Michigan hollies such as ‘Winterberry’ and ‘Sprite’
- Red maple ‘Red Sunset,’ ‘Scarlet Sentinel’
- Sumac ‘Gro-low,’ ‘Laciniata,’ ‘Dissecta’
- Weeping willow (Salix babylonica), most oft-cultivated form is female
- Yew ‘Brownii,’ ‘Densiformis,’ ‘Emerald Spreader,’ ‘Fastigiata,’ ‘Repandens,’ ‘Sentinalis,’ ‘Wardii’ (Note: When grown without male company, these females will bear no fruit.)
Some male varieties sold as pollinators or ‘seedless’ forms:
- Ash tree ‘Autumn Purple,’ ‘Marshall’s Seedless’
- Bayberry shrub ‘Myriman’
- Box elder tree ‘Sensation’
- Cork tree ‘His Majesty,’ ‘Macho,’ ‘Shademaster’
- Cottonwood ‘Colmar,’ ‘Red Caudina,’ ‘Siouxland’
- Evergreen holly** ‘Blue Stallion,’ ‘Blue Prince,’ ‘China Boy,’ etc.
- Fringetree (Chionanthus) ‘Floyd’
- Ginkgo tree, most named varieties including ‘Autumn Gold,’ ‘Princeton Sentry,’ ‘Shangri-la’
- Junipers: Juniperus chinensis ‘Pfitzeriana,’ ‘Pfitzeriana Glauca’; J. horizontalis ‘Bar Harbor,’ ‘Jade River,’ ‘Jade Spreader,’ ‘Plumosa’; J. sabina ‘Broadmoor’; J. virginiana ‘Manhattan Blue’
- ‘Lombardy’ poplar
- Michigan holly** ‘Apollo,’ etc.
- Mulberry ‘Chaparral’
- Red maple ‘Autumn Blaze,’ ‘Autumn Flame,’ ‘Celebration,’ ‘Karpick,’ ‘Northwood,’ (most males are less red in spring than females)
- Silver maple ‘Silver Queen’ (you read that right, the queen’s a “he”)
** These species’ males are not the worst of the lot, as their pollen is heavy, rather than wind-borne.
Article by Janet Macunovich and photos by Steven Nikkila, www.gardenatoz.com.
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