Friday, May 11, 2007

Garden Alternatives to Invasive Species in the Mid Atlantic region

For many gardeners, the read word “Invasive” spreads terror and discord and creates great waves of anxiety and negative waves of resentment. Currently, invasive plants defined to be non-native, exotic, aliens which reproduce furiously replacing native species and complex self-sustaining eco-systems with, in some cases, biological deserts or mono-cultures.

The very reasons, which sustain invasive plants, also find their way into gardens and horticulture. Cheap to propagate, easy to grow, indestructible under all conditions, and easy for the consumer to find have the makings for a champion garden trade species. And the wider the conditions a plant may grow in, the wider the trade in the plant, and, so, the wider the distribution to places and eco-systems which can not tolerate the incursion of the new species.

One way to think of invasive species is to think of all the weeds, we do not want in our gardens. The worse ones are those that creep in from our neighbors untended mini-estates. Think running bamboo, and understand the feelings of those who are charged with protecting natural areas. They are gardening with a native only concept, and we are gardening with the anything goes model. This situation makes for uneasy neighbors, and opportunities for stress and misunderstandings.

Not all invasive species were introduced by gardeners or garden centers. Many simply hitched a ride on the bottom of a boot or in the cargo hold of a transport ship; even in the crates of packing materials we use to ship our consumer goods have held invasive surprises. But some, like kudzu were originally introduced by the horticulture industry (1876), even though it took federal help to find its place in our southern landscapes. Callery pear hybrids abound in the mid Atlantic region as a highly recognizable invasive species, and are still recommended by local government agencies (Prince George’s County Tree) as a street tree choice, even though, the tree is almost always a bad long term landscaping solution.

Who are some of the bad actors and what can we replace them with? Lythrum, purple loosestrife, a perennial favorite which can be replaced with Liatris spicata, gay feather or blazing star, is an excellent native alternative for Lythrum. Liatris is easily grown in average, medium wet, well-drained soils in full sun. Though preferring moist, fertile soils and tolerant of poor soils, drought, summer heat and humidity, Liatris can be intolerant of wet soils in winter. The 2 foot tall clump forming perennial has long spikes of rounded, fluffy, deep purple flower heads, appearing atop rigid, erect, leafy flower stalks. [picture of Liatris courtsy of]

If you are seeking a long summer bloomer to match the floral display of Lythrum, try hybrid hibiscus such as Lord Baltimore. Huge flowers, reliably perennial and fast growing, this plant will fill the summer and fall garden with knock your socks off beauty until frost. Liking wet soils, I have seen them tolerate some fairly dry conditions, and since they grow so fast, they can out-compete many pests, such as another invasive species, the Japanese beetle.

Another bad actor is English ivy. Drive through rock Creek Park in Washington or the grounds of my house, and probably your house, too, and the evergreen vine which is pulling off all the lateral branches of the shade trees is Hedera helix. Just a note, if it is not native and is just greening up now in the spring, and is climbing your trees, it is our native poison ivy.

It is tough to beat English ivy for an all purpose practical, indestructible, inexpensive, easy-to-grow, ground cover. You do not need to weed it, feed it, water it, mow it, trim it or think about it until it pulls down a major shade tree or your gutter system to your house. [picture of wisteria courtesy of Larry Hurley]

A good alternative native to the eastern United States is Pachysandra procumbens. Not the evergreen Pachysandra you are used to seeing everywhere; that one is not native, and shows up on some good plants gone bad lists. Alleghany spurge is nest in rich most soils and grows to around 12 inches high when happy. In mild winters it may be, in protected areas, partially evergreen, this species can grow in shade to part shade settings.
[picture of pachysandra courtesy of ©2006 by Will Cook ]

Another great native alternative, Polystichum acrostichoides, Christmas fern, grows in the natural areas of the mid Atlantic. An absolutely wonderful, shade loving, no-maintenance plant, it has the additional feature of being evergreen. Planted in a massing, many times found under trees, and often seen in quite dry conditions, this 24 inch tall species is workhorse of the shade garden.

And speaking of workhorses, the large rodent-garden-eat-all on stilts, the native eastern white-tailed deer pauses and seeks alternative plants, choosing almost anything else first, and leaving the ferns alone. I have a rule which states that deer eat five hundred dollar exotics first, followed by many rare and endangered natives second, and then pretty much everything else. The Christmas fern manages to find a way of the dinner menu and thus is a perfect choice for a native, natural, and non controversial landscape solution.

There are other Maryland natives which are easily found in nurseries and can be used as ground covers. Tiarella cordifolia, foam flower, with white flowers and a preference for most shade locations, and, Phlox stolonifera, woodland phlox, in pinks, blues, and whites, which rise to 8 inches tall when in bloom in April.

English ivy is a vine; as a rule, vines are bad. Of course this is a glittering generality, but listing horticultural vines which have gotten loose in natural areas, is a listing of naturalists’ most abhorred. Porcelain berry, Japanese and Chinese wisteria, Asiatic Bittersweet, Japanese or Hall’s Honeysuckle these plants terrorize natural areas and native eco-systems. But all is not lost, for there are many native alternatives such as Wisteria frutescens, American wisteria, which produces a gentler-not-so-over-the-top inflorescence and a willingness to live with its neighbors gentling draping itself across lateral tree branches. While the native wisteria is fragrant is not as overwhelming as the ostentatious oriental cousin. [picture of wisteria courtesy of Larry Hurley]

If you are in need of good old American aggression and want to go native, then Campsis radicans, trumpet vine is for you. This native can be quite aggressive, but at the same time provide brilliantly colored flowers which serve to attract hummingbirds. The yellow or red flowers are true show stoppers, but be warned, this can be a match for mere human buildings and endeavors.
[picture of trumpet vine courtesy of: Virginia Lohr, Professor, E-mail: Department of Horticulture and Landscape Architecture Washington State University ]

For those who recall the lazy days of humid Maryland summers and the scent of honey suckle, you are recalling, most likely, a nativist’s nightmare. The overpowering fragrance comes from the exotic species of Asia, but there is a native, coral honeysuckle, Lonicera sempervirens, which, while not beckoning one to sip the nectar, makes quite a plea for hummingbirds to stop on their way. Red to orangey-pink flowers in early summer spectacularly enhance this well behaved native vine which can grow to twelve feet in moist full sun soils.

There are those of us who plant theme gardens in the hope of attracting specific visitors. One of the most familiar themes is that of the “butterfly”: garden, perhaps another would be that of a “native” garden or perhaps both together. A quick choice would be to plant a butterfly bush, Buddleia davidii, but alas that would remove you from your double themed goal, because there is some evidence of the exotic’s spread by seed into natural areas, and because it is not native. So, although, there are those who are not ready to condemn the exotic Buddleia, if you are looking for sure-bet native alternatives, then Eupatoriums, maculatum and dubium, could be a possibility. Going by the common name of Joe Pye Weed, which is not exactly a great marketing name, the Eupatoriums are butterfly magnets, full sun to light shade, they are stunning summer flowers for full sun to part shade moist settings. Beware, they are rather large, 4 to 8 feet, so give them room and watch the butterflies come.

And do not forget the native asters as alternatives to butterfly bush, and please do not confuse butterfly bush, Buddleia, with butterfly flower, Asclepia incarnate and Asclepia tuberose are native, wonderful and worthy for your native butterfly garden. A fragrant species of late fall blooming, butterfly attracting aster is Aster oblongifoliusRaydon’s Favorite”. Asters want full sun and limited love. Turn them loose in your garden and let them be; perfect for the summer-time soldier-gardener. There are so many asters to choose from including New England asters, Aster noviae-angliae, bushy asters, Aster dumosus and many more.

I would be remiss if I did not sing the praises of summersweet, Clethra alnifolia. Though most cultivars grow in the four to eight foot range, there is a 30 inch cultivar named “16 Candles”. Fragrant white flowers or, if you want, light pink found on the aptly named “Ruby Spice”, the summer flowering Clethra grows in light shade to full sun in moist soil. When you plant this note that in natural settings it grows near stream beds and so the moister the soils, the happier the plant. Need I mention that water logged is not moist; near not in will give you a over-the-top alternative to Buddleia. [picture of clethra courtesy of:]

The watch word here is fear not the invasive species controversy. You can still garden; you can still have diversity; you can still create haven of personal satisfaction and enjoyment, and you can achieve this by using native alternatives. Personal choice and environmental responsibility can be part of your gardening traditions. We have only scratched the surface. Barberry can be replaced by Itea virginica, sweetspire, or Ilex verticillata, winterberry; Euonymus alatus, by Itea again or Aronia arbutifolia, chokeberry; Bradford and other hybrid flowering pears with Amelanchier laevis, Allegheny Serviceberry, Crataegus viridis, Hawthorne, Chionathis virginicus, Virginia fringe tree, or Oxydendrum arboretum, sourwood.

When choosing plants for your garden, you should know the needs of each plant you select. Does it need light or shade; what are the optimum soil types; how wet or dry is best for your species; and what are the potential impacts on your immediate and regional eco-system? Native alternatives reduce the environmental impact possibilities allowing you to concentrate on the right plant in the right place.

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