Invasive plants can be beautiful but they are also destructive. Gardeners are becoming more aware of the dangers of invasive plants, as well as the benefits of pollinator plants. We are now realizing there is more to designing our gardens than aesthetics. We have to consider our environment, how plants and wildlife interact.
One of the most common and often used invasive shrubs is Burning bush, Euonymus alatas. It is popular for its beautiful red foliage in the fall. As pretty as these shrubs are, they set so much seed that they quickly force out other plants. At the same time there are a number of other shrubs that can provide similar color and benefit.
The large Fothergilla major can grow as tall as six feet with an even wider spread. A dwarf version, F. gardenia, will grow about two to four feet tall with a three to four foot spread. Fothergillas have attractive bottle-brush flowers in the spring, and foliage that turns shades of yellow, orange and red in the fall. The Fothergilla on the Bridge of Flowers always attracts a lot of attention for its unusual flowers. It is a hardy, trouble free shrub.
Other substitutes for burning bush are chokeberry, enkianthus, highbush blueberry, Virginia sweetspire, and American cranberry bush viburnam.
We don’t often think of trees being invasive, but the Norway maple outcompetes sugar maples in woodland. It also has such a dense canopy that its shades out and reduces wildflower diversity. There are alternatives. The red maple and sugar maple have similar golden foliage in the fall. The red oak has deep red foliage in the fall. There is no need ever to plant a Norway maple.
Some Norway maples have deep purple foliage, but substitutes include crabapples; be sure to look for disease resistant cultivars. European beech and redbuds, also have deep red autumnal foliage.
Japanese barberry, Berberis thunbergii, is used as hedging, but I have never understood why it is popular. All those thorns! It is another invasive plant that has a number of alternatives to its color, its berries and form. Some weigela and ninebark cultivars provide purple foliage while others provide yellow autumnal leaves. Virginia sweetspire and highbush blueberries provide red autumnal color. Deutzia gracilis and Potentilla fruticosa are small rounded shrubs that bloom, respectively, in spring and summer.
European barberry is also an invasive shrub, often used as hedging. Weigela, ninebark, bayberry (Myrica pensylvanica), inkberry and Virginia sweetspire are all possible alternatives.
I have a Rhus aromatica in my garden. This is a very low-growing sumac that can spread to six or eight feet across. The foliage turns yellow and red in the fall. It has very few problems and tolerates my wet garden even though it is said to prefer well-drained soil. I like it because it provides quiet interest for my garden which has so many larger shrubs.
Rusty willow (Salix atrocinerea) grows to about 40 feet and Gray willow (S. cinerea) only grows to a shrubby 15-20 feet, but both are vigorously taking over wetlands in Massachusetts and elsewhere. Their seeds are distributed by the wind, and they easily hybridize with other willows. This means they can make our native willows extinct.
The invasive trees and shrubs I have mentioned are all forbidden in Massachusetts, and there are alternatives for all of them. It is pretty easy to cut down these trees or dig up and get rid of these invasive shrubs. Other invasives are not so easily removed, but efforts must and are being employed.
Purple loosestrife is a lovely plant that was accidentally brought to the U.S. from Europe. It is often seen along roadsides where it is damp or swampy. The damage of this plant, and others, is that it overcomes native plants and reduces needed food, shelter, and nesting sites for birds and other wildlife.
When I see a few purple loosestrife plants growing along a damp roadside it is easy to stop and pull them out. A large stand along a highway wetland is a different story. In the 1980s researchers went to Europe to look for insects that might prey on this plant. Out of the 120 species they studied they found three that fed on purple loosestrife. They did not feed on other plants.
Galerucella calmariensis and Galerucella pusilla are two of the species that have been imported and used to eradicate purple loosestrife in Rhode Island and Connecticut with good results, especially in sunny areas. The number of these insects is increasing and the research is continuing.
I mention this Integrated Pest Management Technique to remind us all that there are many ways to eliminate invasive species other than hitting them with strong pesticides.
Massachusetts has a long list of invasive and soon to be invasive plants which you can find listed at https://www.mass.gov/service-details/invasive-plants. Some of these plants will be familiar like yellow iris, and phragmites which grow in wet locations and oriental bittersweet that drapes itself over trees. Others like Euphorbia esula L. (Leafy spurge) are not familiar but equally dangerous. ###
Between the Rows April 27, 2019