We're far enough into the growing season that the bindweeds are flowering and the dandelions are ready for a second round of flowers. I try to weed part of the yard every day.
One thing I noticed was that although my lawn started the season full of dandelions, my prairie did not. My prairie is maybe 500 square feet that I planted with native grasses and forbs (non-grass herbs) a decade ago. It isn't a great success--some weedy grasses are too common--but I don't water it and my maintenance is confined to weeding out exotics and occasionally cutting back the grasses to mimic natural disturbance such as bison grazing. By the time I got to the 800th tiny dandelion plant in the lawn--an area the size of the prairie--I was struck by the fact that there were only a couple dandelions in the prairie.
What does that suggest?
One deduction is about plant communities; healthy native plant communities are hard for aliens to invade. Not impossible, but much more resistant than most lawns and gardens. (Commercial weed control websites say much the same; make your grass healthy and thick to reduce dandelions.) Ecologists noticed this pattern long ago and made it into an axiom. But they had to retreat when they found example after example of exotics invading good or pretty good native communities. You can't count on a community keeping weeds out, for two reasons. One is, most of our native communities have at least minor recurrent disturbance from humans (hiking trails!) along which invading weeds can move, little gaps of open ground welcoming the weed seed. Secondly, among all the weeds in the world, there will be one that can invade any particular native ecosystem. The closed community keeps out 99 weeds, but that one gets in. My prairie isn't dandelion-free, but there were only a dozen plants, nothing like the number in my rather neglected lawn. So it is generally true that healthy native ecosystems resist invasion.
|my bluegrass lawn|
The second idea I took from the distribution of my dandelions was about dandelions themselves. We hate them as weeds, but they are plants adapted to lawns and yards, and to moderately disturbed paths and roadsides. They don't grow well in prairies, forests, or deserts. Thus, horrible weeds are a function of both the weed and the habitat. Particular plants are bad weeds in habitats where they grow well, but often they are unaggressive in other habitats. I am growing both creeping buttercup (Ranunculus repens, buttercup family, Ranunculaceae) and creeping Jenny (Lysimachia nummularia, primrose family, Primulaceae) as ground covers. They are not very invasive in my yard. I read about people in Ohio fighting to keep them from taking over. I don't see that. But Colorado is much drier than Ohio, and apparently creeping buttercup and creeping jenny like more rain that my yard provides.
|creeping buttercup, Ranunculus repens|
|creeping jenny, Lysimachia nummularia|
Gardeners are generally aware that environments differ. The USDA Plant Zones define different growing seasons with more or fewer days between the last and first frost, and we know planting a plant in a zone where it is not said to be hardy is a gamble. Gardeners in Colorado are very conscious of the water requirements of plants. Here, if the plant likes it moist, it will likely die if not given substantial supplemental water. Plants with medium water requirements do okay, but rarely thrive. The plants that like it dry or very dry are the ones Coloradans can count on. And then there is drainage. Some plants flourish in a periodically waterlogged soil, others don't grow well unless the soil is well-drained.
We put these ideas together for the seeds and plants we buy, but not so often for the weeds that trouble us. The aggravating weeds are the ones for which my yard has their favorite combination of growing season, water, soil, shade, etc. My neighbor's shadier yard will favor slightly different weeds. If I removed my trees and stopped supplemental watering, I'd significantly change the combination of weeds I fight.
|early spring dandelion in the lawn|
To the degree that yards across the U.S. resemble each other, with Kentucky bluegrass (Poa pratensis, grass family, Poaceae, originally from Eurasia) and the the growing conditions it likes, we all share the weeds that also like those conditions
Alas, for all my wisdom, I will still have to patrol my lawn, digging out dandelions, pulling other weeds.
|another dandelion! --between the flowerbeds|
But my conclusion is also that there will always be weeds. If dandelions suddenly ceased to exist, some other plant would take over the spots the dandelions vacated. And, "be careful what you wish for." Dandelions are hard to kill, but they are not spiny or toxic and can be eaten if you are ever in a famine.
Comments and corrections welcome.