There are a huge number of perennial plants, some hardy and others that are not very well adapted to severe conditions whether hot or cold. Herbaceous perennials usually live for at least three years and grow for several seasons before their tops die back to the ground before winter. But some will live through the winter months without protection and others don’t do well in regions where summers are hot and humid.
Perennial plants can spread, though some spread more aggressively than others. Also, they spread in different ways. Some spread by self-seeding while others have suckers that grow from their roots away from the stem. Some spread via underground stems (rhizomes). Then some have above-ground stems (stolons) that spread, while others have above-ground runners.
What Makes Plants Invasive?
As National Geographic points out, invasive plant species reproduce quickly in new environments where they don’t belong. But to be considered invasive, they must also reproduce quickly and be harmful to property, native plants, or animals of the region.
Invasive plants have certain characteristics that contribute to their ability to outcompete native species and thrive in new habitats. As mentioned above, they spread in various ways, which enables them to establish and expand rapidly, out-competing slower-growing native plants.
They often produce large quantities of seeds and have very effective dispersal mechanisms. This enables the seeds to reach new areas and establish themselves.
In their native habitat, plants are often kept in check by herbivores, insects, or diseases that have evolved to feed on them. In new environments where these natural controls are absent, invasive plants can grow unchecked, without the same level of predation or disease pressure.
Additionally, invasive plants are often highly adaptable and they can thrive in a wide range of environmental conditions. When they are introduced to a new environment outside of their native range, invasive plants may escape the natural checks and balances that regulate their population size and growth.
Are perennial plants invasive?
Perennial plants can be invasive, but many aren’t. A vast range of perennial plants, including many spreading perennials and perennial flowers aren’t invasive, even when introduced into new environments.
Another factor is that different perennials, including plants and flowers, are invasive in different areas. So, a plant that is invasive in some places, will coexist harmoniously with other plant species and won’t be a threat to other native ecosystems.
For this reason, it’s important to familiarize yourself with invasive species so that you can avoid them. If you know what you’re looking for, you can remove them when and if they spread naturally.
What perennial plants are invasive?
Having said that different perennial plants are invasive in different areas, it’s useful to know that many university extensions and state environmental departments produce guides to invasive plants in different areas.
Invasive Perennial Plants in Connecticut
The Connecticut River Coastal Conservation District, Inc., has an online publication, Invasive Plants In Your Backyard! A Guide to Their Identification and Control.
Some of the invasive perennial plants they mention include:
- Black Swallow-Wort, a perennial twining vine that is spread through rhizomes and seeds
- Goutweed, an aggressive perennial ground cover that also spreads by rhizomes
- Japanese Knotweed, a shrubby, upright perennial that spreads from long rhizomes and winged fruit that carries seeds
- Mugwort, a perennial weed that thrives in well-drained soil
Invasive Perennial Plants in Michigan
Similarly, Michigan State University Extension has produced A Field Identification Guide to Invasive Plants in Michigan’s Natural Communities. While they feature some of the same invasive perennials found in Connecticut, many are different.
These include the pretty Multiflora Rosa, a dense, deciduous perennial shrub that produces seeds that are dispersed by birds and animals. The seeds remain viable for 10-20 years making the plant difficult to control once it is established.
Another plant with pretty perennial flowers is the Japanese Honeysuckle, a woody vine that can reach more than 20 feet. It often covers trees, shrubs, and other plants, smothering them. Kudzu, which is invasive throughout the southeastern U.S. is another aggressive perennial vine that forms mats over trees and even small buildings.
Baby’s Breath, often used in flower arrangements, is another perennial plant considered to be invasive in Michigan. So, too, is Dame’s Rocket, a lovely showy invasive plant with perennial flowers that grow in well-drained soil. Both of these are native to Europe and not the U.S.
Others include the Giant Hogweed, Leafy Spurge, and several invasive perennial grasses. Giant Knotweed is a particularly nasty invasive perennial because its sap can cause severe skin burns when exposed to sunlight.
Considerations for perennial plants
It should probably go without saying, but if you are planning on growing perennials, make sure that you don’t plant anything that is invasive within your environment. A good choice in many areas is Black Eyed Susan, a popular perennial plant from the Asteraceae family native to North America.
Black Eyed Susan is one of those perennials that will self-seed and naturalize in some areas but won’t spread aggressively. Other perennial plants that have a similar growth pattern include New England Aster, Butterfly Weed, Purple Coneflower, and Wild Bergamot.
These are all native perennial plants that generally have beautiful blooms, attract pollinators, and can enhance biodiversity without harming the surrounding ecosystem.
There are also many perennial medicinal plants that you can plant safely in most areas. They include Chamomile, St. John’s Wort, Valerian, and Calendula.
Just be aware that in some areas, medicinal plants including Echinacea, Peppermint, and Lemon Balm can become invasive.
Other considerations will be exactly the same as for any other plants. For example, some prefer dry conditions, some like well-drained soil, some prefer growing in full sun, and others like shady conditions.
Conclusion
While some perennial plants, including spreading perennials, are invasive, not all of them are aggressive spreaders. Some may have limited spreading capabilities while others require specific conditions to reproduce, grow, or spread.
The extent and methods of spreading can vary greatly among different perennial species. Do your homework before you plant perennials to make sure you don’t introduce invasive species that will spread and smother other plants.
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