Sunday, May 3, 2020

The two faces of Imperata cylindrica (Japanese Blood Grass or Cogon Grass)

The red form of Imperata cylindrica (usually called Japanese Blood Grass here in the USA) is my favorite ornamental.

But what some people might not know is that this species has a dark side too. It also exists as a wild, non-ornamental form that is considered one of the top 10 invasive plants in the world, Cogongrass.

Wild cogongrass (c) Keisotyo from Wikipedia
The wild form of I. cylindrica is much larger and much more robust than the ornamental variety, and it does not have any red tinge to the leaves. It spreads rapidly through its very tough and sharp rhizomes, forming dense monotypic stands that displace and exclude other plants, which in turn negatively affects all the animals that depend on those plants.

The ornamental form is smaller, mostly sterile, and is much slower growing than the wild form. It also has attractive red leaves that make it a prized specimen among ornamental grass aficionados.

Unfortunately, under certain conditions, this ornamental form can revert back to the wild form or produce seeds, and so Japanese Blood Grass cannot be sold, traded, or grown in quite a few states.

Comparison of greenhouse grown Imperata cylindrica var. koenigii (Japanese blood grass), Reverted I. cylindrica var. koenigii (JBG Revert) and I. cylindrica (Wild-type cogongrass). (c) Cseke, L. J., Talley, S. M. A
I have grown the ornamental form for years now, and it is definitely a somewhat slow grower, and pure stands of the grass can be invaded and overwhelmed by other plants. Growers of this species should try to plant it in dense groupings from the beginning, then weed out any other plants that try to get into such stands. They should also be aware that this is not a bunch grass, but that it forms underground rhizomes that will pop out blades of grass distant from the main grouping.

If you are in a growing zone where there is no chance of the ornamental form reverting to the wild state, then this species can be a striking addition to your collection or garden.

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