The thing with invasive species is that most of them are eye-catching. They look great in bouquets, landscapes, and other decorative places. And for that reason, people want them in their homes. Before they know it, they have planted these invasive species over a wide area and are grappling with means to control their growth. That is the situation many people have faced with the Spiraea japonica. This plant is a known invasive, and in this article we will talk about how to get rid of Spiraea japonica in your yard.
It is a lovely shrub that produces beautiful pinkish flowers that would make any garden look amazing. Plus, it works great for landscapes as it creates a continuous breathtaking layer. But before you think of having it around your home, you should know that Spiraea Japonica is invasive. So much so that studies as to its effects in Buffalo Mountain in Floyd County have come to light. But that is not the only affected area, as many more regions have suffered the cruel fate of its spread.
Fun Fact
The Japanese Spiraea (Spiraea japonica L.), also known as the Japanese Meadowsweet, belongs to the rose (Rosaceae) family!
Spiraea japonica description
The Spiraea japonica comes from the rose family, which would explain its undeniable beauty. It is native to China, Korea, and Japan. It did not come to the United States by accident, as has been the case with many invasive species. But instead, its introduction was intentional. People saw its beauty and wanted to introduce it to the world. Over time, it spread over vast areas in the eastern and Midwestern regions of the United States. To date, these regions record high numbers of this naturalized species.
Why naturalized? Well, this term refers to a non-native plant whose characteristics enable it to survive devoid of human help. It can spread its roots with ease and can also reproduce without human aid. This species falls under this category.
Have you heard of other Spiraea species? That would not be a surprise as the Spiraea japonica is just but one out of more than eighty species in the United States. In most cases, you will find these species in use as ornamental shrubs. It owes to their low heights, compactness, and beautiful flowers. They would make for lovely garden hedges, which would be beautiful throughout the seasons.
These species are common along water sources such as rivers and streams. They also prefer being in wet regions as well as areas where soils experience high levels of disturbance. Examples of disturbed areas would be forest trails and edges, roadsides and fields.
The Spiraea japonica is like other species in its category. In its native growing regions, it would prefer moist areas. But in the United States, it adapts to the existing conditions. While it would do best in the full glare of the sun, it would still grow when in shaded areas. The same goes for soil. As much as it would thrive most in moist and nutrient-rich soil, it would still grow in other soil types.
Growth of the Spiraea japonica
One plant can produce hundreds of seeds each year, which allows them to spread throughout the year. Dispersal of these seeds takes place through water. Given that these plants often establish around water sources, this form of distribution works well. Once a seed finds itself in the soil, it can remain there for years on end without losing its viability.
If a seed is in ideal conditions, it takes root and grows at a fast rate. In doing so, it creates dense growth, which is hard to penetrate. Where there are gaps around it, it quickly fills them as it spreads outwards. The problem with this is that the plant will occupy canopy gaps in woodlands. And this would affect other vegetation in the area.
What’s worse is that this species is very competitive. So, where it comes across native plants that are not as competitive, it will have the upper hand regarding water and nutrients uptake. In the end, you will find that native plants are on the low while those of the Spiraea japonica are steadily growing. It can be a big problem where threatened species are in play.
An excellent example of such a species would be the Virginia Spiraea. Unlike the Spiraea japonica, the latter is a native species to the United States. Its numbers have been on the decline owing to invasion by plants such as the Japanese Spiraea.
For this reason, the Spiraea japonica is on the ‘do not plant’ list. Unfortunately, it is still available in many nurseries across the globe. And this undermines the efforts in place to control Spiraea japonica.
It currently ranks as a medium risk invasive plant, which makes it problematic. But not big enough of a problem to be a high-risk plant. However, time will tell.
How to Identify Spiraea japonica
How can you tell that you are dealing with a Spiraea japonica invasion? Here are some features you should be on the lookout for:
This perennial shrub has slender stems that stand erect. If the species is under ideal conditions, the stems can be as tall as 6.5 feet. They have hues ranging from brown to reddish-brown. At the base, they are smooth, but as you go up heading to the branches, hairs start to increase. At the tips, hair growth should be dense.
The buds on the stems are minute with rounded to triangular shapes. They also seem flattened.
The leaves alternate and are ovate with saw-like edges. Depending on the prevalent conditions, they can be as long as three to four and a half inches. Their widths lie between one and one and a half inches.
Spiraea Japonica leaves
Their flowers are pinkish and can either be a deep pink or a pale one. They are not large, and they measure about 0.2 inches each. However, they seem bigger than this as they appear in compound corymbs on wide branches. Their blooming periods are between June and August.
Spiraea Japonica flowers
This species bears fruits with seeds in the ranges of 0.09 to 0.1 inches. You can find the seeds in a smooth capsule.
Have you seen a plant that meets the above description? If so, you could be dealing with the Spiraea japonica.
Lookalikes
Before you cut down that bush, here is a lookalike that could be growing in your outdoors- the Spiraea Virginiana. This plant also goes by the name Virginia Meadowsweet. It falls under federal protection as it is under threat. The difference between it and the Spiraea japonica lies in the appearance of flowers. If they are white, then you are dealing with the Virginiana Meadowsweet. If they are pink, you could have the culprit.
Another similar species would be the Spiraea Tomentosa. It is also native and has pink flowers. The variation in this species is that its flowers grow in upright panicles as opposed to the Japanese Spiraea, whose flowers are in rounded corymbs. Plus, these two species occupy different areas. In the boggy areas, you will find the Tomentosa while the Spiraea japonica prefers upland soils.
How to get rid of Spiraea japonica
Invasive species adversely affect the environment. The Spiraea japonica spreads at a fast rate, overtaking native species in the region. It grows in many sites ranging from meadows to forest openings to roadsides. When the seeds spread, they remain viable for many years. As soon as they get the required growing conditions, they sprout and take root. As such, restoring native plants becomes a hurdle.
To make things worse, the Spiraea japonica produces hundreds of seeds in a year, adding to the ones in circulation. These spread by water, and where the plant is near a water source, the dispersal method takes place fast. Other than by dirt, the seeds can also get dispersed through transportation. Take an example of a construction site. As the team clears the area and moves the soil, it would pick up the seeds and move them to new locations.
As of this time, there have been no adverse reports of this species affecting animals. However, it has reduced the native plants on which they can feed, which is on the negative side.
Management
Prevention
Some people come across this species in their yard and think that because they are not near water, it cannot spread. While that may cover one of the dispersal methods, it does not cover dispersal by soil. Also, when the seeds on the parent plant touch the ground, they could sprout. And this could go on and on until the area fills with these plants.
If you spot this plant near your home, it is best to get rid of Spiraea japonica. Subsequent monitoring should follow this elimination to ensure that seeds do not sprout in the now bare land.
Control
Mechanical control
When you have a few bushes in your yard, you can opt to deal with them by hand. The same goes for where you cannot use herbicides on the bushes owing to desirable plants in the area. Using mechanical removal is not permanent as it does not deal with the roots. Instead, it keeps the plants from growing upward and outward by maintaining them at a given level.
However, using this method is a sure way to keep seed production at bay and monitor the control of the bushes. If you do not plan on using the land for other uses, you can use this method.
Note that this species re-sprouts after cutting, and you will need to continue the mowing to exhaust its energy reserves. Do the cutting at least once each growing season before seed production starts. Where possible, cut close to the ground.
Chemical control
In this method, you attack the species on two fronts: the stump and the leaves. Note that chemical use around water sources should be minimal. And where you have to use one, get a chemical that is suitable for use around such environments. Abide by the rules of the manufacturer, for your safety and that of desirable plants.
Foliar Application
Note that the use of the chemical will be subject to the stipulations of the manufacturer. Some chemicals are so strong that a wrongly directed spray could kill the native plants in the region. Where possible, get a herbicide that you can use without fear of killing desirable plants.
Start by making a mix of the herbicide using the prescribed amounts before directing the spray on the leaves. In doing so, aim to thoroughly wet the leaves such that the mixture starts dripping from the plant.
Also, schedule the spraying for a calm day to avoid spreading the chemical over a large area. Ideally, the application should take place when the air temperatures are above sixty-five degrees Fahrenheit, as this will encourage the absorption of the chemicals.
Glyphosate or Triclopyr will have the best results, apply a 2% solution and water plus 0.5% non-ionic surfactant.
Stump Application
In some cases, you may find that applying a herbicide on foliage could threaten other species in the area. In this case, you can use this method. It also works for people dealing with a few bushes.
Start by cutting the stems of the bushes at the ground level – if you cannot get to this level, cut as close to it as you can. Do not let time pass after this and immediately apply a herbicide mix of your choice. The proportions should be in line with the manufacturer’s guidelines. Ensure that you cover the entire surface with the chemical.
For this method, Glyphosate or Triclopyr will work. Apply a 25% solution of glyphosate or Triclopyr and water to the stump.
Cultural Control
If mowing and chemical applications do not appeal to you, cultural control is another option. Purchase native Spiraea species and plant them near the invasive species to control the growth of the Spiraea japonica.
Conclusion
Spiraea japonica, though not a high-risk invasive plant, could invade your yard within a short period. It is best to nip it in the bud while you have the chance.
References
Invasive Plants in Pennsylvania Japanese Spiraea Spiraea japonica – http://www.docs.dcnr.pa.gov/cs/groups/public/documents/document/dcnr_010259.pdf
Southeast Exotic Pest Plant Council Invasive Plant Manual – https://www.se-eppc.org/manual/japspiraea.html
Spiraea japonica – http://www.iucngisd.org/gisd/species.php?sc=622
Spiraea L. spirea – https://www.fs.fed.us/rm/pubs_other/wo_AgricHandbook727/wo_AgricHandbook727_1067_1070.pdf
Exotic Invasive of the Quarter: Japanese spiraea Spiraea japonica – https://forestupdate.frec.vt.edu/content/dam/forestupdate_frec_vt_edu/newsletter/archives/2019/33_4/GagnonSpiraea.pdf
