We are two or three weeks into it, with several more weeks to go: hay fever season.
The late summer/early fall bout of the stuff is blamed primarily on ragweed, an ignominious green plant that seems to grow everywhere.
The problem with ragweed, and many other plants, is that they produce copious quantities of pollen, mostly from male flowers which are the primary sources of the irritations related to hay fever.
Not all plants contribute to the problem. The common flowering Golden Rod (Solidago) is often confused with ragweed as they bloom at about the same time. However, Golden Rod pollen is sticky and does not float through the air like ragweed pollen.
To determine the plants that stimulate allergic reactions in allergy-sufferers, a scale has been established. The OPALS (Ogren Plant Allergy Scale) rating for plants is now coming into common use in places like the U.K. and the United States, however it is still slow to catch on here. Perhaps more retailers would be inclined if consumers demanded the information.
The OPALS scale is a scale of 1-10, with 1 being least bothersome and 10 being most. Similar to growing zones, which serve as a guide to a plant’s winter hardiness, the OPALS number can help guide consumers according to what plants are best suited for low-allergens.
In the absence of labelling, here is a list of the common plants from the top and bottom of the OPALS scale:
Elevated risk (9 or 10 on the OPALS scale)
The plants that we tend to use in our gardens that are highest on the OPALS scale include:
Yews (Taxus). The male flowers rank as a 10, female only 1. Generally, yews are not labelled “male” or “female” but you can often tell the females as they are the only ones with red berries on them. Note that the berries are toxic as is the pollen on both the male and female.
Juniper (Juniperus). There are many junipers available through garden retailers and none of them, in our experience, are labelled as to male and female.
Oak (Quercus) and Alder (Alnus). Both hardwood, deciduous trees flower in mid to late spring and produce a lot of wind-borne pollen. Rubrum Maple, “Autumn Glory” is a suitable alternative.
Privet (Ligustrum). This popular hedging plant blooms in early July and produces loads of allergy inducing male-flowering pollen.
Low risk (one or two on the OPALS scale):
Violets. Be aware that perennial violets are aggressive, even invasive. They are just short enough to escape the blades of a lawn mower. Do not plant violets near your lawn or you may find that you no longer have one.
Foxglove (Digitalis). A reliably winter hardy bi-annual. Plant in a protected place, out of direct afternoon sun and allow the flowers to mature into seed pods that will self-sow, creating baby foxgloves late this season or early next.
Impatiens. We are not recommending the previously very popular “walleriana” type as current varieties on the market are not resistant to downy mildew (yet!). Look for Sunshine impatiens and be prepared to water regularly.
Fir trees (Abies). All fir trees produce a sticky pollen that does not travel extensively by wind and does not promote an allergic reaction. Our favourite species is Abies Concolour or Silver Fir for striking appearance. Grows to 12 metres or 40 feet tall.
Campanula. An extensive family of herbaceous perennials that varies in height from a ground covering 10 cm to about a metre high. Check out the selection at your garden retailer and choose your favourites.
Coral Bells (Heuchera). A popular flowering perennial that adds much colour and character to flower borders. Look for Amber Waves and Chocolate Ruffles, our two favourite varieties.
Rubrum Maple Autumn Glory (Acer rubrum, Autumn Glory) is a stunner in mid to late October, with brilliant red foliage. This variety is sterile and therefore does not flower.
Allergies? No problem — let the allergy sufferers enjoy the garden again.
More info at http://www.heatlthyschoolyards.org.
Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son Ben is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at markcullen.com, @markcullengardening, on Facebook and bi-weekly on Global TV’s National Morning Show.