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Blue Grama Grass

The shortgrass prairies of North America that once covered half the center of the continent were a plant community adapted to hot, dry summers, drought, and grazing by vast herds of bison. Of all the plants in the shortgrass prairies, blue grama grass contributed the highest productivity, thanks to its tolerance for a wide range of soils and its efficiency at converting sunlight into plant matter.

Blue grama grass uses sunlight by the C4 cycle, which is more efficient during hot days and nights than the C3 cycle used by most plants native to temperate zones. (Though many plants live by the C4 cycle, most are native to tropical climates.)

However, at first glance, blue grama grass seems ordinary. It is under two feet tall, with narrow leaves and wiry seedstalks. The leaves rise upright in a loose bunch, then arch near the top, giving the plant a relaxed look. From a distance it looks airy, even wispy.

That changes in late summer, when the seedstalks rise. My plant is five years old and makes dozens of seedstalks. At the tip, each branches sideways with a short stem that is lined by twenty or more pendent seeds, like the teeth on a comb. I have a feeling that the bison dined well in late summer.

You can also glimpse the vigor of blue grama grass when you dig up a plant. The roots crowd together in a disk up to four feet across and a foot thick. Meanwhile a column of roots descends as deep as six feet, an adaptation for surviving drought and prairie fires.

A young plant looks like a bunch grass, that is, it has a small footprint from which emerge the leaves and seedstalks, bunched together. But the footprint grows. Underground stems called tillers grow away from the mother plant and turn up at the tip to start new plants. My first plant arrived in a two-inch pot five years ago and now is five distinct plants grouped together in an area that is four feet square.

With its low height and fine texture, blue grama grass deserves a spot in the garden. It can front a border, edge a path or grow in a group for a contrast of texture with perennials such as purple coneflower and black-eyed Susan. Beware, however. It can be weedy. Every year, my plant makes several dozen seedlings all around it and in the lawn. They root fast. I have to hoe them in the garden and dig them from the lawn. Last year, I changed tactics and cut off the seedstalks before the seeds matured. I had no weeding to do but I lost the spectacle of the seedheads dancing in the breeze.

Blue grama grass today covers North America from the Rockies to the Mississippi and Mexico to Canada (it’s the state grass of Colorado and New Mexico). This huge range is the main reason that it is one of the “Calibration” species that provide data for the National Phenology Network (USA-NPN). Volunteers far and wide record the date when plants show the first bit of green leaf, when the tiny flowers appear, and when the seeds mature.

Phenology is about the timing of events in the lives of plants and animals. By recording the dates, we have data to compare over decades. It’s one way we can sense global warming. We gardeners gain too by having dates we can use to time sowing, pruning, tilling and harvest.

By Mark Kane - the Groundskeeper, YourGardenShow.com

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