Plant This, Not That
Purple Edition
I’m a sucker for purple in the garden. Lavender, lilac, violet, periwinkle, plum, amethyst, violet, you name the shade – if a plant has some of it in its flowers, foliage or even name, I’ll be drawn to it like a bee to pollen. I mean, I could barely contain my excitement when I learned there’s an ornamental grass called purple lovegrass (Eragrostis spectabilis). Woot!
But not all purple plants are created equal. Some are invasive and thus a threat to our fragile ecosystems. So for my fellow purple-fanciers out there, here are some examples of lovely but lousy plants, along with some equally lovely but laudable native alternatives.
Invasive: Purple Loosestrife (Lythrum salicaria)
Native to Europe, Asia and northwest Africa, purple loosestrife is a menace to North American wetlands. It invades wet meadows, marshes, river and stream banks, pond edges, lake shores, reservoirs and ditches. It establishes itself quickly and replaces native vegetation with dense, homogeneous stands that reduce local biodiversity, endanger rare species and provide little value to wildlife. It now occurs in every U.S. state except Florida. Although most states list it as invasive and a dozen regulate its sale, it’s still widely available for purchase.
Native Alternatives: Blazing star (Liatris spp.), blue vervain (Verbena spp.) and ironweed (Vernonia spp.).
There’s a blazing star species for just about every part of the country. They vary in form and size, but they all share a spiky purple habit that’s irresistible to native bees, butterflies, birds and me. They bloom from the top down, which makes the description of them I recently heard -- "sparklers for the summer garden" -- absolutely perfect, particularly on this July 4!
Blue vervain grows in almost every state of the continental U.S. Its blue-purple flowers are held aloft on candelabra-like spikes. It attracts bees and birds and is a larval host to butterflies like the common buckeye.
Most parts of the U.S. can claim one or more ironweed species as native. New York ironweed (Vernonia novaborecensis), for example, can reach eight feet tall. It bears reddish-purple daisy-shaped flowers at the top. It’s beloved by butterflies and birds.
Invasive: Butterfly Bush (Buddleia davidii)
This deciduous shrub, also known as summer lilac, has conical flower clusters and an intoxicating spicy-sweet scent. I may or may not have fallen victim to its charms in the past. It’s native to China. Imported to the U.S. for its ornamental value, it has since invaded disturbed sites, river banks, reforested areas and open fields in the Northeast, Southeast, mid-Atlantic and western U.S. The National Park Service recently advised its volunteer “weed warriors” in the DC area to remove any butterfly bush they see in national parks (such as Rock Creek Park), because it’s one of several species that have “escaped” residential landscapes and become a threat.
Butterfly bush matures quickly, producing up to 40,000 seeds in a single flower spike. These travel long distances by wind and water and have a germination rate of 80 percent or above. The seeds remain viable in soil for up to five years. Although butterflies will drink its nectar, their larvae cannot survive on it. It forms dense thickets, precluding other growth and displacing native larval food sources.
Butterfly bush is a good reminder that a) just because you don’t see an invasive plant marching toward the local park, that doesn’t mean it isn’t and b) just because it has nectar and attracts pollinators, that doesn’t mean it’s actually supporting those pollinators or providing other critical ecosystem functions.
Several states in the Mid-Atlantic, Midwest and West Coast have listed or regulated butterfly bush, but you can find the shrubs for sale in just about any mainstream nursery.
Native Alternatives: Texas mountain laurel (Sophora secundiflora), American beautyberry (Callicarpa americana), meadowsweet (Spiraea spp.) and blueblossom (Ceanothus thyrsiflorus).
Texas mountain laurel is native only in Texas and New Mexico, which is unfortunate for the rest of us. It’s an evergreen shrub with showy spring blossoms that smell a bit like grape soda. It attracts butterflies and other insect pollinators.
Once you’ve seen American beautyberry, you’ll be hooked. Magenta berries hug the arching branches in the fall. Those berries are an important food for many birds, including the northern bobwhite. It’s native to the southeastern U.S.
Around the country there are a dozen or more native meadowsweet, or Spiraea, species, many of them with flowers in the purply-pinky spectrum. Spiraea tomentosa, for example, is native to the Northeast, mid-Atlantic and Southeast and sports rose-purple flame-shaped blooms in the late summer. It’s a larval host and attracts birds and butterflies. Spiraea splendens is native to the West coast and has clusters of dark pink to purple flowers.
Okay, it’s not technically purple. But for you West Coasters, how about blueblossom? It’s a large evergreen shrub with a bounty of pale indigo flowers in the spring. It attracts lots of native bees.
Remember, always confirm that a plant you’re considering is native to your own ecoregion and suited to your own light, moisture and soil conditions.
I’m confident you’ll sleep more soundly tonight knowing that even the purple-addicted among us have plenty of native perennials and shrubs to choose from.
As for music, I’m thinking this song needs no introduction:
Resources
Jill Swearingen, et. al., Plant Invaders of Mid-Atlantic Natural Areas, 4th edition, National Park Service and U.S. Fish and Wildlife Service, 2010.
Invasive Plant Atlas of the United States, University of Georgia and National Park Service.