Goldenrod & Ragweed

Most of you know that goldenrod (Solidago sp.) is Nebraska’s state flower.  A late summer perennial that thrives in full sun with some species doing well in dappled shade.  Goldenrod is a beacon for many of our pollinating insects feeding on the nectar and collecting the pollen.  It isn’t uncommon to see a wide array of insects such as monarch butterflies, flies, beetles, and native bees with many being a specialist.

However, goldenrod gets a bad rap.  While it is beneficial to many insects it is often mistaken for fall allergies.  The real culprit to most allergies suffers is goldenrods close cousin, ragweed (Ambrosia sp.).  Goldenrod is an insect pollinated plant where as ragweed relies on the wind to deliver pollen.  In order to ensure successful pollination one healthy ragweed plant can release up to 1-billion grains of pollen.  The University of Tulsa estimates that one million tons of ragweed pollen are produced each year in North America.

I think you are going to need another tissue.

1,000,000, tons of pollen.  The standard size of a pollen grain is downright tiny (about 15 microns).  Pollen shed is greatly influenced by the weather.  Warm, dry weather favors the greatest pollen shed and peeking in mid-September.  With 21 species of ragweed found throughout North America is isn’t uncommon for plants responsible for your suffering to be located hundreds miles away.  Since ragweed pollen is such a problem nationwide it is often used as a standard when doing quality control studies for air filters.

Now going back to goldenrod.  Most plants grow between 2’-4’ in height with some reaching over 5’.  Depending on the literature there are close to a dozen species of goldenrod found throughout the state.  Most plants grow in full sun with a few exceptions growing in partially-shaded locations.  One thing to keep in mind about goldenrod is their ability to increase in size through stolons (above ground stems).  When choosing a plant for your garden you will want to take that into consideration and plan accordingly.  Also, they prefer dry locations.  When some of our regionally native perennials receive too much moisture they will flop.  To keep goldenrod upright avoid watering.

So the next time someone mistakenly blames goldenrod for their fall allergies let them know that it is really ragweed.

 

Scott Evans
Scott Evans is a horticulture assistant with Nebraska Extension in Douglas-Sarpy Counties. A certified arborist through International Society of Arboirculture and Nebraska Arborist Association. Scott is also Tree Risk Assessment Qualified through ISA. Scott co-leads the Master Gardener program in Douglas & Sarpy counties. Along with volunteer management he provides his expertise with disease and insect identification, lawn and landscape weed management, plant health, and I.P.M. practices. He also enjoys growing many houseplants ranging from African violets to cacti and succulents. Scott has two Bachelors of Science, one in Biology (emphasis in Botany, Ecology and Environmental Science) and second in Environmental Geology from Northwest Missouri State University. He earned his Master of Agriculture from the University of Nebraska-Lincoln.

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