Deep Thoughts on Johnson Grass

by Eric Neubauer

You’d think the hard dry soil would add to the difficulty of pulling up plants, but some of the plants are coming up easily. I’ve often marveled at how fast new shoots can come up.

Just about every Master Naturalist knows that Johnson grass uses stored energy in its rhizomes to do this. There is a cost because the rhizome shrivels up as the new shoot advances. Johnson grass appears to be exceptionally adept in moving its resources around. Even as the water becomes scarce, the shoots keep coming. There is a point when the grass has to stop growing, as it did last summer.

Anyhow, I am amazed that the grass has been undeterred so far except for giving up on inflorescences and at least nothing is presently being added to the seed bank. But I shouldn’t be. As the plants use their stored resources for continued growth, they are metabolizing. The products of metabolism are carbon dioxide (plenty of that around) and water, a scarce commodity. All the plant needs to do is relocate that water to the advancing shoot. Growth can still occur.

Meanwhile, the rhizomes are invisibly shrinking under the surface and the plants can end up being anchored by only a few measly roots. That explains why some plants are easier to pull up now. It also means that rather than digging for rhizomes, it’s only a matter of waiting until they magically turn into shoots and then pull those.