Invasive Plants are a Disruption to Nature
People seem to carry souvenirs with them as they travel. We have always done it. For example, in the early 19th century, well before a rail road existed, Phillip Franz von Siebold lived and collected a large collection of Japanese native plants. Among these were East Asian plants now called hosta in the western world (giboshi in Japan). Fortunately, hostas were controllable in their new habits. They never got grew faster than they could be controlled. Unfortunately this is not the case with other non native plants.
As an example let’s consider kudzu. This was introduced at the Philadelphia Continental Exposition in 1876. In the 1930s and 1940s it was a recommended plant to use for soil erosion. During WWII the US introduced this to South East Asian Island nations. The military did this because the plant grows so fast it could be used as a natural camouflage. Now, as well as in other major western European locations like northern Italy and some parts of Australia to name a few, kudzu has become an international problem. The growth rate of this plant is phenomenal. Without extreme diligence this weed can become nearly impossible to control in our environment.
There are biological/natural as well as a few herbicides being used to control this problem plant. Since I am generally against chemical means for controlling a garden pest whether it is plant or insect I would like to present a couple of physical ways to control kudzu. It will be next to impossible to eradicate 100 percent of the seed. These will present a problem for several years after initial removal of the parent plants. This method of reproduction will need to be supervised for several years. The most time consuming and labor intensive method is to remove the root crown and destroy them. Without the crown any remaining roots will not be able to produce a new plant. I’m sure all the regular gardening readers will just have gasped and run to the refrigerator for a cold beer to calm their nerves. This method is physically demanding. Then you have to make sure you have removed the entire crown. Don’t leave any in soil you may have taken off and plan to send elsewhere where it could start a new colony. No, I think the best method to control this problem is through repeated cutting. This can be done a couple of ways. Several east coast locations have begun to herd goats and lamas where there is infestation. Fresh kudzu is a stupendous foraging plant. This plant is in the pea family so it is even tasty to us human foragers as well. That is why it learned to grow so quickly in the first place. It does not dry and bale up easily to produce a good winter feed reserve. So, kudzu is generally controlled through grazing. If you lack the ordinance for your residential location to raise grazing animals then consider mowing where the plants grew frequently for the next several years.
I frequently encourage tree trimmers to leave unwanted chipped wood to use as a mulch and part of my potting media. One year I received a load late in the season. Since I had already cleaned out some garden beds, I spread a decent layer on top of them, to save myself some time next spring. I was rather proud that I was able to do a spring time chore in the fall. That next summer I had some large weeds come up I knew were going to grow into a larger bush type of plant. Now cursing myself for not letting the green chipped wood sit for a year, I pulled out the numerous weeds that summer that popped up all over the bed. This has been at least the fourth year since I did this rather silly thing and I still pulled up some more of these this spring. I finally got around to looking up what I had sprouting and re-growing from missed root pieces. It turned out to be a bush honeysuckle. This was another of those plants brought from eastern Asia. It can grow to almost 20 feet tall. It was grown as an easy care hedge shrub. It grew so thick that it acted as a superior screen in urban gardens economically.
This is just where the problem lies. It blocks out light for other plants really well. The plant is easily dispersed by birds eating the seed. The shrub grows quickly. It can quickly monopolize large areas in just a couple of years. By quickly usurping the native plants it quickly retards the natural balance. Not all birds eat the berries. This means some species of birds leave the area. Native trees and plants are unable to grow in these thickets. All life dependant on them is disrupted.
Again this plant can be controlled by removing the roots. I learned the hard way to be careful when doing this. When I left just a bit of root a new bush would quickly re-establish itself. The other green method of control is to again repeatedly mow down re-growth. This is the least labor intensive way to control this plant though most time expensive. You will have to do this for a few years because there could potentially be some viable seed. Also, it does take repeated cutting to sufficiently convince a root that re-growth is not possible anymore.
The last invasive plant I wanted to talk about today is Oriental Bittersweet. This was brought to the US in 1879 and soon found its way into being used as a decorative plant. This oriental species produced more abundant seed than the native Bittersweet. This is a very aggressive vine. Cross pollination with the native species produced hybrids that are equally invasive. It will out-compete all native plants in the area. It can grow to 60 feet. The vines adhere to the tree and grow up to the light. Once there it produces a dense canopy that drastically reduces light to the native plants. The berries that were disposed of from decorative arrangements as well as the luscious berries that appeal to a wide host of animals meant that this plant has become a nightmare for half of the country. I accidently left a plant sprout in my yard. By the third season it had completely covered the 12 foot huge Viburnum davidii carlessi. It was at this point I determined just what it was that had sprouted. Now for the next several years I will be cutting down re-growth. Herbicides are not completely effective. The picture of this above is a sprout less than 2 weeks old. This is at least the fourth or fifth time I have cut down re-growth since I first killed the original vine just a month and a half ago!
Perhaps you see a pattern here? Invasive plants are difficult to eradicate. Herbicides, if they are able to damage growth are not only ineffective but tend to be harmful to life. Invasive plants typically require physical removal. There are fledgling businesses that specialize in returning native habitats to their original composition. If it is a smaller garden, such as your own, I recommend repeated cuttings to eliminate the pest plant by finally reducing its vitality so it can not send up new growth. Always be careful introducing non native plants into your garden. Falling under the spell of merchandisers advertising the newest plant on the planet is something we should all be wary about considering. I know it is hard. I know, like me, you may not even know a plant is invasive until well after you bought a plant. That is my experience with lythrum. We just need to be prepared for an extended hardship to eliminate them if they turn out to be undesirable.