Front yard prairie. Photo by D. Sillman
Click for audio: Weeds, the bad
We have been trying to wrestle a patch of cleared ground in the front of our house into a shortgrass prairie, but, along the way, we (and our little patch of prairie) have been overwhelmed by an onslaught of weeds. We planted buffalo grass on the prepared soil in early May and watched the race between the delicate grass shoots and runners and a binging masses of weeds. We had to deal with the weeds in the simplest, but most time consuming way in order to not destroy the delicate, growing grasses around them: they had to be pulled out one by one, roots and all!
When I close my eyes at night, I see weeds spreading out in pinwheel patterns across the soil surface. The weeds have tiny sprigs of buffalo grass coming up in between their long, radial stems. The trick was to get hold of the center of the weed just above the big, central, root and ease it out of the ground. The removed weed then unveiled a patch of young grass which can then grow uninhibited by the overlying weed mass.
Prostrate spurge (Euphorbia humistrata). Photo by D. Sillman
The weeds that were most abundant in the early stages of our prairie were the spurges (especially prostrate spurge (Euphorbia humistrata) and spotted spurge (Euphorbia maculata)). The low-growing, ground hugging stems of these fast growing annuals smother the soil surface and kill the germinating grass. The spurges are a pleasure to rip out of the ground! These two spurges are native species that thrive in compacted, sandy soils in disturbed (especially bare soil) areas. They are not serious competitors for most garden or crop plants because of their low profiles, but are a real threat to developing grasses!
Bindweed (Convolvulus arvensis) was not as abundant as the spurges in our young prairie, but it spread its morning-glory-like vines over the bare soil (and also over the adjacent mulch and bare rocks and even over the concrete of the driveway and sidewalk!) so rapidly that they overwhelmed any other plant that had been growing there. Bindweed is an exotic, invasive perennial with a robust, abiding root mass that might be 10 to 14 feet below the soil’s surface. Lateral roots up to 20 feet long grow off of this central root and then give rise to vertical shoots that turn into rapidly growing plants. These satellite plants send much of their photosynthetic production back down to the central root and race as fast as they can to flower in order to make and then disperse seed. You can pull out or dig up the surface vines of bindweed (it is very satisfying to remove the tangled greenery!), but that laborious cultivation leaves the majority of the plant unaffected.
Bindweed (Convolvulus arvensis). Photo by D. Sillman
The lateral roots of bindweed can suck up so much water from the surface soil layers that it can push the soil past the permanent wilting point for all other plants. Here in the dry soils of Colorado, bindweed can kill off almost all of the other plants that might have grown in a soil system.
Over in the mulched part of the yard, I encountered a dense patch of bindweed coming up through the shredded, cypress-bark just next to an area where I had previously put down landscape cloth under the mulch. I removed the cypress-bark cover over some of the bare soil in a six foot swath next to the landscaped-clothed area and then dug out the surface bindweed plants before laying down a new layer of landscape cloth. There were, though, dozens of twisted, white tendrils coming out from under the adjacent landscape cloth into the formerly mulch-only space. When I came back to the finish the job 48 hours later, all of these thin, white tendrils had thickened into stems and leafed out into vertical, rapidly growing bindweed vines!
The biotic potential of bindweed’s deep root is astounding! It makes me wish I had gotten some glyphosate herbicide on my recent trip to the garden center! We are, though, trying to control our landscaped area without synthetic chemicals!
Kochia (Bassia scoparia). Photo by D. Sillman
Another weed that is just starting to grow in the prairie area is kochia (Bassia scoparia). Kochia is another exotic, invasive, annual plant that has several, weed “superpowers.” First of all, kochia is a C-4 plant. C-4 metabolism is a relatively uncommon adaptation (it is only seen in about 3 % of all terrestrial plant species) that enables a plant to take up carbon dioxide without losing excessive amounts of water via transpiration and especially without exposing some of its delicate, carbon fixing enzymes to toxic levels of oxygen. The bottom line for a C4 plant is that it must spend more energy than other types of plants (which are collectively called the “C3 plants”) to make sugars, but if the stress of drought or arid conditions threaten to dry out a normally transpiring plant, then the extra energy cost is a small payment to insure survival. C-4 plants grow most quickly during times of drought and high temperatures, conditions, of course, that are very common in the middle to late summer.
The recent, rapid growth of kochia in our prairie-to-be reflects its C-4 metabolism and its inherent ability to thrive in times of heat and drought!
Kochia (Bassia scoparia). Photo by Pikist
Kochia also produces abundant, allelopathic chemicals from its roots that can poison other plant species. As it spreads in a soil system, fewer and fewer other plants (which would potentially be competitors for the kochia) are also able to grow there. Crop plants, garden plants and grass plants are all negatively affected by the kochia toxins!
The third weed, “superpower” seen in kochia concerns its ability to make and disperse seeds. Each mature kochia plant can produce almost 15,000 seeds! Further, the above-ground tissues of the senescing (but still seed bearing) kochia can break away from its roots and bounce its way across potential soil habitats spreading its seeds as it goes. In other words, kochia can become a “tumbleweed” just like that other exotic alien plant species that we’ve talked about, Russian thistle (see Signs of Spring 6, April 8, 2021).
Next week: three “good” weeds!