Variegated Japanese knotweed

(Question)

Can this plant become invasive like the plain green leaved Japanese knotweed?

(Answer)

Thanks for getting in touch. You certainly raise an interesting question about whether the variegated cultivar of Fallopia japonica is as invasive as the species Fallopia japonica.

You are clearly aware of the invasive tendency of Fallopia japonica,  the ‘green-leaved Japanese knotweed’ commonly known as Mountain Fleeceflower. It is a major garden thug that is a rampant spreader in most habitats and should be avoided.

However, the variegated form of this plant is an attractive cultivar and may be somewhat less invasive than the former, possibly having a more clumping habit than the species . It has attractive round leaves that maintain their white variegation throughout the season. Although the flowers are not ornamentally significant, the reddish-pink stems add winter interest. Some people report that it is well-behaved in their gardens; others advise caution. Whether it becomes invasive or not probably depends upon several factors.

Japanese knotweed is a dioecious plant, meaning there are male and female plants which require pollination to produce viable seeds. Since most of the plants (cultivars) available from nurseries are presumed to be male-sterile clones (and therefore do not produce pollen), they spread through rhizomes. However, viable seed could be produced if a plant were in proximity to another plant of the same family. Any resulting seedlings would, of course, take after the more invasive parent.

If it were grown in a shady area with well-drained and somewhat dry soil, it would possibly spread less quickly than in a sunny/moist location. One might also consider containing it in the ground within a large plastic pot–the rhizomes would not be able to spread easily outside the pot.

To summarize, even though the variegated Fallopia japonica may be less invasive than the species, it will still require regular care and monitoring to make sure it doesn’t spread more than one desires.

Thank you for your awareness of  an invasive plant species. It is important that we learn to identify and manage invasive plants to protect our local ecosystems.