Adaptations
Since this plant can be found in various locations around the world, it has to have the ability to adapt to different environments. St. John's wort is classified as cyclic, this means that it has significant population swings year to year. Part of this is because it does not flower in the first year of life. The plant generates 15,000 to 30,000 seeds per year and the seeds are viable for 20 years. This time frame allows the seeds to find a comfortable environment to settle and grow in.
Hypericum perforatum has a horizontal spreading root
system, which allows it to grow quickly. This type of root system
does not allow the roots to grow deep into the soil. This root system uses both
seeds and runners, sexual and asexual reproduction. Using both of these forms of reproduction allows
the plant to spread quickly and often. The quick spread of the plant,
multiple forms of reproduction, and the
ability to grow in a harsh enviro
nment makes it a difficult plant to
control.
There have been many techniques in an attempt to control this plant, most of them have been unsuccessful. Mechanical controls include hand pulling, which stimulates the root system to spread quicker, this may be successful if you dig the same area for years. Mowing over the plant does little but may reduce seed production, however the plant is still capable of asexual reproduction. Herbicides have been ineffective since the plant's small surface area prevents the spread. Grazing is also ineffective since the plant leaves contain chemicals that depress the central nervous system in many animals. These chemicals are particularly dangerous to cattle. There is one control system that has been very effective, and is used on the National Bison Range in Montana. They use Chrysolina quadrigemina which are foliage feeding beetles to limit the growth of St. John's wort.