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The Monday Garden
Goldenrod, Ragweed and Mugwort

Issue No. 129 - September 12, 2004
by Sue Sweeney

  
GOLDENROD: The goldenrod's blooming, so it must be fall. Goldenrod's a lovely fall bloomer that's gotten an undeserved bad rap as a major source of allergy-causing pollens. While it’s not pollen-free, it’s not the really bad guy. Goldenrod's a friendly, photogenic native, beloved of birds, and bees, and other beneficial insects. There are at least 130 goldenrod species in North America. There's even a seaside variety and a white one (“silver rod’). It's a great late summer garden plant, too.
 

Picture: One of our beautiful native goldenrods (Solidago) with a beneficial wasp (Bartlett Arboretum, Stamford CT August 2004)

 
The villains are some of those easy-to-overlook weedy things with greenish flower stalks. The worst is the wind-pollinated ragweed, which blooms at the same time, and often grows in the same place as goldenrod, and which also belongs to the Aster (Composite) Family. And then there’s ragweed’s close relative the ubiquitous mugwort, which is also coming into bloom now.
RAGWEED: Starting with ragweed, not only is it the source of much human misery; but we have only ourselves to blame. All ragweed needs to get started is freshly-turned earth to expose the seeds buried in the soil, and a bit of sunshine to wake the seeds up. The seeds will wait in the soil for 40 years for the right conditions to come along before germinating.

Like poison ivy, ragweed’s what we call an “enhanced species” because human behavior gives it a major ecological boost. Ragweeds thrive where the earth has been disturbed. In a way, it’s Mother Nature’s revenge for leaving her earth naked to dry out and erode. Almost daily, I read yet another new article about research confirming that we should disturb the soil as little as possible, and that we need to mulch, mulch, mulch. mulch.

 

picture: common ragweed just before the flower stalks rise. (Bedford Street, Stamford CT September 2004)

 
Ragweed, for example, didn't get out of hand until the European settlers along the East Coast cut down much of the forest and plowed up the land. Indeed, once I read that archeologists date the mud at the bottom of the Long Island Sound by the ragweed pollen count, which rocketed upwards in the 1800's.
 

picture: western ragweed detail (Scalzi Park, Stamford CT, 2004) 

 
There are a good 2 dozen kinds of ragweed; our local ragweeds come in three basic types: common ragweed (Ambrosia artemisiifolia), western ragweed (Ambrosia psilostachya), and giant ragweed (Ambrosia trifida). The common’s usual knee height or less and has deeply cut “raggy” looking leaves. The Western looks like the common only it’s a lot bigger. The giant have rounded leaves with 2 to 5 pointy-tipped lobes and can reach shoulder height or more. The common and giant are annuals; the western can be annual or perennial, spreading by underground roots.
 

Picture: leaf samples from the giant ragweed (Morgan Street, Stamford CT September 2004

 
The three ragweeds have very similar flowers. The tiny flowers along the flower spikes are facing downward; so what you see are the scalloped green flower bases with the flower parts peeking out from underneath like a petticoat. The giant ragweed has tiny gold-yellow flowers; the common ’s are tan.
 

picture: close up view of the flowers of giant ragweed (Scalzi Park, Stamford CT September 2004)

 

pictures: L: common ragweed viewed from a distance R: giant ragweed from a distance
The giant ragweed’s flower stalks are striking green candelabras dusted with gold;
the common’s are smaller and closer together so they like more like a crowd of slightly curved green spires

 
MUGWORT: Now for the mugwort (Artemisia vulgaris), also called “common wormwood”. This one’s an alien, so again, we only have ourselves to blame. It’s another one of the Euro-Asian imported herbs that got out of hand. Along long the East Coast, across the Midwest and in the Northwest, you’ll see the silvery, plumy colonies of mugwort along sidewalks, backyards, parking lots and roadways where we’ve disturbed the earth. It’s related to absinthe and sagebush (not the cooking herb known as “sage”).
 

picture: form, leaf and flower stalk of mugwort, (Morgan Street Stamford CT 2004)

 
USES: Ragweed is useful to non-humans. The oil-rich seeds are good bird food, particularly in winter. Mugwort and ragweed are used in homeopathic medicine. Mugwort, in particular, seems to have a number of useful herbal applications. For example, it’s recommended as an herb for a “sleep pillow” and it’s sold as a lice and mite repellant for caged birds.

Invasive, common-as-mud, allergy-causing mugwort is still sold in nurseries and on-line. The variegated “Oriental Limelight” highbred seems to be very popular. One of my fellow Master Gardener Interns spotted it in a Connecticut nursery this past week, at the amazing price of over $10 a pot. (I wonder what the hapless buyers thought when they later saw mounds of it growing wild by the parking lot!)

 
 

picture: detail of mugwort mature leaf (note the pointed tips)

picture: detail of western ragweed leaf
(note the deep cuts between leaves)

 

picture: mugwort blooming with Joe Pye weed (Scalzi Park Stamford CT September 2004)

 

picture: giant ragweed (Morgan Street Stamford CT 2004)

  
From The Monday Garden. Copyright © by Sue Sweeney. Reproduced with permission. 

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