A hypothesis about the fecundity of Zoysia

Have you ever seen seedheads on zoysia? Have you ever planted zoysia sod and seen a lot of seeds on some pieces but not on others? I’ve seen this a lot, and I’m not the only one. It’s a striking phenomenon.

Korai sod Tetris pic.twitter.com/u61lDKSwwi

— Albert Bancroft (@alban3074) May 2, 2020

I’ve been watching zoysia for a while, trying to figure this out, and I’ve got a hypothesis.

The fecundity of Zoysia (seedhead production) is positively correlated with growth rate.

That’s pretty simple. But in practice, looking at seedheads on lawns or spots fields or especially on golf courses, it may not be so obvious. Why? Because when the growth rate is rapid, the turf tends to be mowed more frequently, and when that happens the seedheads get mown off. Although the seedhead production rate would be higher on such turf, the seedheads are not so visible.

The turf that is growing more slowly doesn’t get mown as frequently, and one sees a lot more seedheads on that turf. But after observing this for a while, I think the seedhead production is the other way around—more seeds on turf that grows more. When you think about it, that makes sense that it should and could be that way, right?

Here’s something I observed on a small island in the Andaman Sea.

There are lawns of manilagrass (Zoysia matrella) growing on the sand beside the beach. Sand is a poor growing medium for plants because it doesn’t hold much plant-available water nor supply many nutrients.

As one botanizes on swards of manilagrass like these, one can see patches of grass that are growing more.

I suspect the increased growth is due to animal waste, or other organic material in the soil¹ that is supplying the grass with a bit more nitrogen and a bit more water, and because of that, there is an increased growth rate.

When one takes a closer look at these patches of manilagrass with the increased growth, as one does when one is botanizing beside the sea on a fine day like this one was, it’s apparent that there are a lot of seedheads where the grass has grown more.

Meanwhile, the surrounding lawns that haven’t grown so much? No seedheads at all.