aliens in your garden
Several years ago, a client asked me to take a look at a Mt. Lebanon garden overwhelmed with two nasty weeds that spread aggressively and thrive in a variety of conditions—wild buttercup (rununculus), and bishop’s weed (aegepodium). Wild buttercup has a profuse yellow blooming stage in April and competes with spring growth of desirable forages. Bishop’s weed has a lovely variegated cultivar with a flower much like Queen Anne’s Lace (and in fact is still sold at local garden centers.) However, when it flowers and subsequently sets seed, birds carry the seeds and drop them on the ground in their own little fertilizer caplets, where they germinate. The new plant is not the lovely variegated form, but reverts to the original green form. Both weeds rob other plants of valuable fertilizer. These monsters—both among the long list of invasive species in Pennsylvania—require chemical warfare, and even then success is fleeting.
There was no need to inform this client of how onerous these pests are—the damage to her garden was the proof she needed. The roots were entwined in every shrub and perennial she has, choking the life out of everything. She would love to be rid of them, and after sending my crew in to fight the good fight for more than five years now by hand pulling, careful spraying and even painting full-strength herbicide concentrate on the plants with a paint brush, we are not even close to being successful.
So what to do? When it comes to invasive plants, sometimes drastic measures are called for. One commercial client’s landscape was overrun with two other invasives—wild morning glory (convolvulus arvensis) and thistle, (cirsium discolor). We concluded that the only way to solve this unsightly problem once and for all was to take everything out of the bed, dispose of it and put the bed on a spraying program by a qualified professional. The client lost thousands of dollars in plants. After a full year of careful spraying, we finally were able to plant up the bed last spring. How did the problem get this bad? In this case, the client had eliminated the chemical weed program offered by his landscaper. He saved money in the short run but paid a higher price in the long run.
So, what is the definition of an invasive plant and why should we care? “Invasive plant” defines a species that has become a weed or a pest. These plants grow and spread in a fiercely aggressive fashion, displacing other plants. They either spread roots that travel several feet underground and send up new plants as they go or grow from seeds that disperse easily, such as dandelions. The worst offenders do both. They are not picky about soil composition or pH and exploit disturbed ground. Highway projects and construction sites, where wild morning glory and thistle arrive first, are common problem places. Both not only spread voraciously by seed, but also have spreading roots up to eight feet long. No amount of hand pulling will solve this problem.
Because invasive plants are almost impossible to control, they can dominate entire areas. A good case in point is the Japanese knotweed (fallopia japonica) taking over along Banksville Road. According to Amy Delach at Defenders of Wildlife, a national conservation organization focused on wildlife and habitat conservation and the safeguarding of biodiversity, the cost to control invasive species and the damages they inflict upon property and natural resources in the U.S. is about $137 billion per year! That’s a lot of money, and much of it is tax dollars.
Most invasives came here from other countries and are often called “exotic,” “alien,” “introduced” or “non-native.” Some were actually brought here to solve problems. According to the website www.Oregon.gov, kudzu which is an aggressive vine literally destroying entire forests in the south by wrapping itself around the canopies of trees and smothering the life out of them, was brought to this country for erosion control and later declared a noxious weed.
Some of the hardiest and most popular landscape plants are on the invasives list, including burning bush (euonymous alta), barberry (berberis vulgaris) and privet (ligustrum ovalifolium). While these plants have a few desirable characteristics, the undesirable characteristics far outweigh the good. Each of these plants has great alternatives: for gorgeous fall color similar to burning bush try our native itea little Henry with a mature height and width of three feet, or Henry’s garnet, which grows to 6’ x 6’ at maturity.
If the lovely burgundy leaf of the barberry is what draws your attention, use physocarpus summer wine, (5’ x 5’) or weigela midnight wine (4‘ x 4’) or wine and roses (18” x 2’). These three shrubs are on my short list of “must use” plants when I design for clients.
Privet has become a pest in major proportions, and did you know it is extremely poisonous? Used most often as a hedge, privet is high maintenance because it grows to 15’ x 15’. Instead, look for shrubs that grow to the height and width you want, like boxwood (buxus), holly (ilex) or one of the new upright yews that are naturally narrow and grow slowly to about 8 feet tall.
For a less formal look, perhaps you would like one of the new forsythia cultivars such as gold tide that grows to 3’ x 3’ at maturity, blooms beautifully and is very easy to maintain.
So while we may know and understand what a weed is in our gardens and how to control it, the issue is larger and more insidious than we realize at first glance. When these weeds take over, we must take steps to keep them at bay. Otherwise, they spread and take over not just our gardens but also our wild areas, overwhelming the forest floor so other native species cannot compete. With no human intervention available, they run rampant robbing our wildlife of food and altering the ecosystem forever. Especially sad is the plight of our Northern songbirds, which need oil called lipid that is found in native dogwoods that cannot compete with the invasives. Although invasives serve as food for local songbirds, they do not provide the nutritional quality needed by the birds for their long migration south.
So what should we do? Here is a list of action items that will deter the aliens and keep your landscape healthy:
- Learn what invasive species look like, and educate others. Check www.invasivespeciesinfo.gov/unitedstates/pa.shtml and www.dcnr.state.pa.us/forestry/plants/invasiveplants/index.htm.
- Say no to planting invasive species.
- Replace invasives if they are in your landscape with native plants and their cultivars, especially those that provide a valuable food source for wildlife.
- Minimize disturbance to your lanscape.
- Protect healthy plants that are native to this region.
- Choose organic fertilizers and minimize the use of chemical fertilizers.
- Scout for exotic pests regularly and dispose of them wisely before they take over.
- Clean gardening equipment that has been used in an area having invasives.
Protecting your garden by planting non-invasive plants will save you time and frustration down the road, protect our forest areas from invasives and help keep our ecosystem balanced and healthy.
Claire Schuchman is a local landscape designer and Phipps master gardener. Claire.Schuchman@gmail.com