Buffalobur (Solanium rostatum). Photo by D. Sillman
Click for audio: The shortgrass prairie and weeds
The Penn State Extension states that “a weed is a plant out of place, not intentionally sown, whose undesirable qualities outweigh its good points.” This is a very relativistic definition of a weed and emphasizes that in some plant communities a “weed” might have an important, functional role while in others it is a destructive presence.
There is no scientific definition of a “weed,” it is not a botanical classification. From an individual human point of view, a plant is a “weed” if it strikes you as “undesirable” in whatever environment or situation it is growing. Any plant can be a “weed” in just the right (or wrong) context. Plants are weeds depending on the eye (and botanical prejudices) of the beholder!
Ralph Waldo Emerson said, “What is a weed? A plant whose virtues have not yet been discovered.” Some people relaying that definition almost always add that it is surprisingly mild considering that Emerson was an avid gardener and, like most of us who garden, probably spent a great deal of his time and energy pulling and hoeing (if not outright cursing!) weeds!
Catmint (Nepeta mussinii). Photo by D. Sillman
Weeds compete with “desirable” plants for space, for light, for nutrients, and for water. Here in arid, Northern Colorado the water-stealing features of a weed can be incredibly compelling! A plant can also express its “inner weediness” by growing very rapidly or growing on top of the other plants around it! Weeds also may be poisonous or irritating, or they may house or sustain plant pathogens or pests. They might also do damage to roads, sidewalks, drains, etc. “Undesirable” can be expressed in many dimensions, but most plants are called “weeds” simply because they are not the plants an observer (or gardener) wants to see!
Weeds, though, can also hold vegetative ecosystems together. They can provide food for many herbivores and pollinators (and even people!), and they can express their own qualities of aesthetic beauty and grace. According to the concepts of the “suburbitat,” the importance of many weeds in the life cycles of native insects (which are, in turn, both pollinators and also food for native birds) is far more important than their potentially negative aesthetic or horticultural impacts on the suburban landscape.
Deborah and I have almost always been extremely tolerant of weeds in our fields, flower beds and yards, tolerant, possibly, to the point of being enabling). We have been engaged in a project over the past few months, though, that has made us look at some weeds with a very different eye.
Photo by D. Sillman
As I wrote last August (Signs of Summer 13, August 27, 2020), according to the extension office at Colorado State University most lawns in Colorado are a mix of Kentucky bluegrass, tall fescue and perennial rye. These plants are all exotic species! “Kentucky” bluegrass is an introduced plant native to Europe, Asia, and northern Africa! It is incredibly common in lawns all across the United States and Canada but is classified as an invasive and destructive plant (a “weed!”) in most natural grasslands. Tall fescue is also an introduced grass species that thrives in marginal environments primarily because of a endo-symbiotic fungus. That fungal symbiont, however, has toxic effects on horses or cattle that might graze on it. Perennial rye grass is also an exotic, introduced plant species that is native to Europe, Asia and northern Africa.
So the lawns we see in our neighborhoods are green swaths of exotic and, potentially, invasive and toxic plant species! Add to these disturbing features that fact that a bluegrass lawn, according to the Colorado State Extension service, requires 2.5 inches of water a week in order to survive! Over the five, “Colorado summer” months (May through September) that would mean that a bluegrass lawn will consume 55 inches of water! That represents almost 400% of the average annual rainfall here in northern Colorado! All of that additional water has to come out of your water tap, and its cost has to come out of your bank account!
Shortgrass prairie. Photo by B. Snyder. Wikimedia Commons
Shortgrass prairie is the grassland biome that grows and thrives under arid to semi-arid conditions. About half of the original short grass prairie still exists in the center of North America over to the eastern side of the Rocky Mountains. This is a region of extreme summer drought and irregular delivery of moisture.
There are two dominant grasses that make up between 70 and 90% of the plants in these shortgrass prairies: buffalo grass (Boutelouia dadyloides) and blue grama grass (Boutelouia gracilis). There are, though, many other plants that make up the complex flora community of this biome.
A preserved piece of the original, vast, shortgrass prairie can be found in the Pawnee National Grasslands of northeastern Colorado. In 1998 D. L. Hazlett published (USDA-FS) a guide to the vascular plants of the Pawnee Grasslands. Hazlett identified 521 species of plants in the grasslands but noted that 115 of these (22%) were non-native species (I think that we can rightfully call these plants “weeds”). These weeds are not only taking up space and water in these dry grasslands, but also may be actively inhibiting or interfering with the growth and development of many of its critical plants. This altered prairie ecosystem is less productive, is capable of supporting fewer animals and is less sustainable than the prairie in its original conformation.
Buffalo grass. Photo by J. Tann, Wikimedia Commons
Deborah and I decided to try to recreate a small piece of shortgrass prairie right here in Greeley, Colorado. As part of our xeriscaping of our yard, we removed all of the bluegrass/fescue lawn and left about half of it (about 1300 square feet) to be converted into prairie. The other half we bordered with rock “dry creek beds” and heavily mulched around a set of planting circles into which we planted native, flowering perennials, yuccas and cactuses.
This spring we tilled the prairie area and
Blue grama grass. Photo by S. E. Wilco, Wikimedia Commons
spread a good layer of compost over it. We then seeded it with buffalo grass (in May) and then over-seeded it with a mix of buffalo grass and blue grama (in mid-June). The May seeding germinated slowly but, eventually grew into a 30 or 40% surface cover of buffalo grass along with a 60 to 70% cover of some remarkably hearty and tenacious weeds!
Before we could do the June over-seeding of our prairie-to-be, though, we had to remove those weeds. The list of species that were growing in this limited area is impressive as were the weight and volume of pulled weeds (great thanks to Waste Management for hauling them all away!). Some of the most abundant weeds in the yard were field bindweed, Canada thistle, buffalobur, lambs quarters, kochia, spurge (both spotted and prostrate), common purslane, catmint and storksbill.
Next week: more on these weeds! I will talk about weeds that are “bad,” and then, the week after, weeds that are “good!”