CO-Horts Blog

Tuesday, July 18, 2017

When Beauty IS the Beast

When Beauty IS the Beast
By Irene Shonle, CSU Extension in Gilpin County.

What would you say if your neighbor told you she was growing a plant that was beautiful, long-blooming, drought-tolerant, deer-resistant, and spreads very quickly?  You might say, “Sounds too good to be true.”  In fact, it may be too good to be true.  Here in Colorado, we have a problem with many non-native “invasive ornamental” plants which do too well in our climate, and have escaped from cultivation and are wreaking havoc in our natural areas.  Many of these are on our State Noxious Weed List, making them illegal to sell or plant.   As gardeners, it is our responsibility to know these plants, and avoid planting them.

The Brooklyn Botanical Gardens estimates that there are 300 dangerously invasive weeds present in the continental U.S. and Canada and of these, half were introduced as ornamentals. They were brought to this country intentionally and allowed to gain a foothold before their harmful effects were known.  
When they arrived in this country, none of the mechanisms that keep plants in check, such as insects, disease, and competition came with them.  In natural areas, unmanaged populations can displace native plants, reduce biological diversity and alter ecosystem processes. These impacts affect bird, insect, fish and mammal populations which depend upon native plants for food, shelter, and protection from predators.

Is it possible to plant invasive ornamentals responsibly?
Not really. As soon as the "responsible" gardener who knows about the plant’s invasive characteristics is out of the picture (moves away, gives away cuttings or transplants, goes on vacation), the plant has the chance of becoming a problem. Also, seeds can be eaten by birds, carried by cars, dogs, or the wind and then may be planted in new locations. Gardeners, no matter how diligent, cannot control for natural processes.

What can I do?
  • Choose native or non-invasive plants for your garden.
  • Do not plant invasive ornamentals. Remove any invasive ornamentals in your garden.
  • Become familiar with invasive species and report their presence on public lands.
  • Ask your greenhouse and/or nursery to stock more natives and no invasive non-natives.

Two resources to learn more about native plants include the CSU Extension Native Plant Master Program ( and the Colorado Native Plant Society (

Our worst ornamental invaders
Our worst ornamental invaders in Colorado include: purple loosestrife, ox-eye daisy, Russian olive, tamarisk, Bouncing Bet, Dame’s/sweet rocket, perennial sweet pea, Dalmatian toadflax, yellow toadflax/butter and eggs, Mediterranean sage, common tansy, scentless chamomile, and myrtle spurge. 

Purple Loosestrife (Image :City of Boulder)
Purple Loosestrife (Lythrum salicaria) is an extremely aggressive weed which is overtaking U.S. wetlands at the alarming rate of 475,000 acres each year. It thrives in moist soil--near rivers, streams, irrigation canals, drainage ditches, lake shores, wet meadows and marshes. It's easiest to identify when the purple-magenta flowers bloom from mid-June through mid-September. The blossoms have five to six petals and grow in clusters at the end of long spikes. Each plant is capable of producing 1-3 million seeds annually. Some cultivars carry the claim of sterility but recent research has shown that these varieties can and do produce viable seeds.
Planting Alternatives: Spotted gayfeather, (Liatris punctata) Russian sage (Perovskia), butterfly bush (Buddleia), Delphinium or larkspur, blue vervain, lavender, wild lupine, violet sage (Salvia x superba), Fireweed (Epilobium spp).

Oxeye daisy
Oxeye daisy (Chrysanthemum leucanthemum or Leucanthemum vulgare) A member of the Sunflower family, is an erect perennial plant with white ray and yellow disk flowers which bloom from June through August. A native of Eurasia, this aggressive plant has escaped cultivation and become a troublesome weed in the mountains. In Crested Butte, the “Wildflower capital,” this plant is crowding out many of the wildflowers they are famous for.
 Planting Alternatives: native daisies (Erigeron spp), Shasta daisy, Black-eyed Susan (Rudbeckia hirta), and Blanket Flower (Gaillardia aristata), and native yarrow (Achillea lanulosa).
Scentless chamomile
Scentless chamomile (Tripleurospermum inodora) is very similar to Oxeye daisy, except it has ferny leaves and is an annual.  It is very aggressive in seeding disturbed areas in the mountains.  
See oxeye daisy for planting alternatives. 

Yellow toadflax
Yellow toadflax (Linaria vulgaris) is so widespread that you can often find it mistakenly listed as a native wildflower in field guides, and not as a noxious weed.  Unfortunately it still is sold by some seed companies as “butter and eggs” or as “wild snapdragons.” Always look on the back of wildflower seed mixes for a listing of what's included in the mix. If toadflaxes are listed, PLEASE DO NOT buy that product.  Yellow toadflax is adapted to a variety of site conditions, from moist to dry and does well in all types of soils. Because of its early vigorous growth, extensive underground root system, and effective seed dispersal methods, yellow toadflax is difficult to control. 
 Planting Alternatives: Annual snapdragons, Coreopsis, yellow columbine (\2001 Plant Select® selection Aquilegia chrysantha ‘Denver Gold’), or the 1999 selection SilverbladeTM Evening Primrose, (Oenothera macrocarpa spp. incana 'Silver Blade'), Golden Banner (Thermopsis spp.), Wallflower (Erysimum asperum, Showy goldeneye (Heliomeris multiflora).

Dame's Rocket
Dame’s Rocket (Hesperis matronalis) is also known a Dame’s Violet or sweet rocket..  It tends to invade riparian and wetland habitat, but can also “naturalize” in other habitats.  It can still be found in “wildflower” seed mixes. If Dame’s Rocket is listed, PLEASE DO NOT buy that product.  This native of Europe may be either a biennial or perennial, and may be from 1-1/2 to 4 feet tall, while flowers range in color from white to pink to purple. There are four petals, which help to distinguish it from phlox. Dame’s Rocket flowers from April through July.

Planting Alternatives: Blue Columbine (Aquilegia caerulea) Native Bee Balm (Monarda fistulosa menthaefolia), woodland phlox (Phlox divaricata 'Chattahoochee). Native harebells, (Campanula rotundifolia), Showy locoweed (Oxytropis lambertii)

Bouncing Bet. Photo credite: John M. Randall/The Nature Conservancy
Bouncing Bet (Saponaria officinalis) can form dense stands of plants, especially in disturbed areas as along roadsides.  It grows up to three feet tall, with clusters of pink to white flowers on the tops of the plants.  Each flower has five petals, all with a distinctive notch at the end.  The plant has a strong creeping rootstock and opposite, strap-like leaves.  It flowers from July to September.
  Planting alternative: Garden phlox, (Phlox paniculata), the 2000 Plant Select®  selection Prairie Jewel Penstemon, Rocky Mtn beeplant (Cleome serrulata),


  1. How can one distinguish Oxeye daisy (Chrysanthemum leucanthemum or Leucanthemum vulgare) from Shasta daisy (Leucanthemum × superbum)?

  2. Great article Irene. Nice that you included substitutes.

  3. Amen, Sister! I'd consider 'Snow in the Mountains' or Aegopodium podagraria L. in this list for its survival mechanics. I've been experiencing its creep from a neighbor. I spent an hour carefully digging up three plants that made it across the edging barrier to see how it grows. I see now why it's successful. These three have been 'foamed' with triple strength Roundup for three months to no avail.
    Your message is a serious reminder that we cannot control all we grow despite our pride. Go natives.

  4. Thank you very much for sharing such a beautiful article.


  5. Most of the time I don’t make comments on websites, but I'd like to say that this article really forced me to do so. Really nice post!
    דירה דיסקרטית