CO-Horts Blog

Monday, September 11, 2017

Maligned plants

By Irene Shonle, Gilpin County Extension

Today, as I was trying to convince someone yet again about how goldenrod (a great late-summer native pollinator plant) is probably not to blame for their fall allergy woes, I got to thinking about other plants that get maligned, either by mistaken ID or by mistaken causation.
Native goldenrod

First, let’s get back to goldenrod (Solidago spp): people are often horrified when I recommend planting it.  They look at me as though I’ve just suggested that they invite a serial killer to bunk with them.  They shake their heads vigorously, and talk about how allergic they are to goldenrod.  But here’s the thing.  Goldenrod is an insect-pollinated plant, and therefore has less pollen, and the pollen is usually a bit heavier. It has the misfortune of blooming at the same time as ragweed, a wind-pollinated plant that sends out copious amounts of pollen, and is a proven allergen. It’s just that ragweed is an inconspicuous plant, and so when people are looking around for something to blame, they see the bright blooms of goldenrod just starting to bloom, and blame it. Granted, there are a few people who have genuine goldenrod allergies, but most people (unless they’ve had it tested), are blaming the wrong plant.  Chances are, you could safely enjoy this plant in your garden.

Another plant that people often mistakenly blame for their allergies is cottonwood – specifically, the “cotton” that flies every June.  This is something that I  believed as a child – I was genuinely frightened of the cotton because I blamed it for my itchy eyes, scratchy throat and sneezing.  I even once made my family move away from a perfect campsite under a huge cottonwood with flying cotton one time to a much less desirable spot in full sun.  Sigh.  If only I had known then that there is no pollen in the cotton – just seeds.  The pollen comes much earlier in the season. However, the cotton is a very attention-getting phenomenon, and it usually occurs about the same time that many grasses are beginning to release pollen, which is usually the true allergen (for me, smooth brome was the culprit). It's possible grass pollen could collect in the cotton, which would then turn it back into a potential problem.

Another plant suggestion that receives skeptical looks is sumac (Rhus spp). People who come from the Eastern U.S. instantly think that all sumacs are poison sumacs and thereby deprive themselves of a lovely native that contributes much color to the fall garden.  While some people are very sensitive to all members of the family, including mangoes, most people have no trouble with our native species (Rhus trilobata and Rhus glabra).
Native three-lobed sumac

Finally, with the advent of social media, I get calls many times a year with people who have read about the dangers of giant hogweed, and think they have found a population and want it taken care of immediately. This is because of all the Facebook and other social media posts warning people about the dangers of Giant hogweed.  And it is indeed dangerous: Heracleum mantegazzianum is a Federally listed noxious weed. Its sap can cause severe skin and eye irritation, painful blistering, permanent scarring and blindness. People can be exposed to the sap by brushing against the bristles on the stem or breaking the stem or leaves.  The problem is that it does not occur in Colorado (at least not yet). What people are finding is our native Cow parsnip (Heracleum sphondylium), which is related and looks somewhat similar.  Cow parsnip is a native plant (not a noxious weed), and doesn’t usually produce any rashes, and many people consider it an edible plant. Just to make things confusing, though, some individual plants mah produce fouranocoumarins, which can cause phototoxicity; most of the reports seem to come from European populations. I have not heard of issues with Colorado populations, but there may be some.  For more information on hogweed and lookalikes, this page has good information:

Cow parsnip, Heracleum sphondylium, a  native plant (

 Can you think of other maligned plants?


  1. Don't forget the much-maligned, yet well-adapted ornamental juniper. In the garden, it takes heat, drought and freezes without a second thought. Right plant, right place is needed to pick a good cultivar for the application though.

  2. Your blog is very useful for me,Thanks for your sharing.