How Horseweed Stampedes Other Plants

•  It reproduces primarily by seed, in wild profusion: 10,000 to 250,000 seeds per plant. Fuzzy tufts of parachute-like hairs, that help seeds fly, grow atop hard seedcases that last for 20 years.

•  Seeds can germinate year round, but 80% emerge as deceptively pretty rosettes in fall when competition is low. It attracts pollinators, but also self-pollinates.

•  Strong taproot plus fibrous secondary roots anchor it, even in airless soil, and help it to spread.

•  Forms large, horse-nose height colonies up to 10’ tall that can dominate tough, but sunny sites.

•  Its leaves and flowers taste bitter and irritate nose, eyes and guts of cattle. As cattle graze on its nearby competitors, Horseweed opportunistically takes over.

•  Its leaves may cause skin irritations in allergic people. Wear gloves.

•  It alleolopathically deters germination of Tomato, Radish, Millet, Corn, Mungbean and Wheat.

•  It hosts crop diseases.

•  Herbicides will not reign it in.

While it cooperates in our eco-system better than non-natives and farmers used to consider it an easily managed annual, this native has become tough to manage recently. Some farmers use herbicide-heavy “conservation tillage”: instead of plowing, they leave crop stubble behind, overplant the area with seeds of “GMOs”, or genetically modified organisms, designed to resist herbicides. Then they spray the whole planted field with herbicide to theoretically give GMOs the advantage over herbicide-sensitive weeds. The genetically nimble herbicide-resistant Horseweed numbers gain the same advantage as GMOs. Alas, Horseweed grows faster than and outrivals GMO Soybean, Sugar beets, or Cotton to reduce these crop yields by 40-80%.

It grows in new beds especially on top of hardpan, where rainwater lingers and helps seeds germinate. It also grows amidst fresh crops as well as in waste areas, like near the railroad station, or in any overgrazed, overworked, sunny, exposed soil. Disruption welcomes this pioneer annual.

I learned about Horseweed the hard way. I initially started gardening in sandy loam in Long Island, NY and was quite surprised when I moved to my newly built home on hard clay soil in Virginia. I had never used a pick axe before. I needed one once I moved. I covered sunny soil, compacted from recent construction, with compost and irrigated it well. The result: a stampede of Horseweed that overtook my intentional plantings. I now hoe or pull it out regularly to hold it back, especially in late fall through early spring, when fewer other plants bloom. I also add lots of compost to beds regularly to help aerate and loosen up the dense clay.

Tips to Corral Horseweed

Mow, hoe or pull out while its roots engage in forming tender seedlings, young rosettes, buds, flowers or seeds, when it becomes most visible and vulnerable, to reign in seed production. Don’t let it go to seed. Add compost and calcium and encourage competitors to shade it out.

Above: Horseweed rosettes look deceptively symmetrical and even pretty, but… Horseweed soon forms a weedy colony

Invasive Oriental bittersweet, Celastrus orbiculatus, (Q#3) or Bramble vines (Q#3) can also make a backyard look scary, impenetrable, and neglected.

EXCEPT

Sometimes untidy growth befits a cultivar. Choice Rose hybrids look uneven, thorny, and wild before they bloom, even after careful pruning. So you need to recognize the growth stages of your chosen plants, and untidiness ALONE does not define a plant as a weed.

Above: Only a Rosarian, who knows its potential, could love this thorny tangle that will soon become a Rosy standout

The ripening foliage of Daffodils is so unattractive that there are those (like Martha Stewart) who braid the yellowing ripening leaves. Yet Daffodils need this quiet photosynthetic period to prepare them to look quintessentially tidy and glorious in their full bloom the following spring.

And some weeds grow into tidy clumps like Heal-all, Prunella vulgaris (Q#1) or pyramidal masterpieces like viciously invasive Garlic mustard, Alliaria petiolata (Q#4). This provides these weedy survivors far better disguises than that adopted by ungainly Horseweed.

B. Are its flowers tiny or inconspicuous?

Weeds have evolved to need little help to reproduce, so they don’t always have the kind of showy flowers that draws in the birds, the bees, the butterflies, or that prolific plant breeder, man.

Flashy flowers may have partially evolved to lure human intervention to assist in propagation. In his book, “The Botany of Desire”, Michael Pollan asks if the Tulip has bent us to its purposes by meeting our desires for beauty. He opines that the plants that man selects get an extra survival boost. Just as a young beautiful woman attracts eager male volunteers to help her procreate (and vice versa), the prettiest plants get lots of help in their reproductive needs. Lacking such enticing charms, many weeds survive anyway, if they have enough resources to get away with the little care they take for their appearance or personality according to human and pollinator tastes alike. Like those folks who present as obnoxious, ugly or toxic, but who have power or great wealth—they don’t need large gorgeous blooms, or other attractive outward charms to reproduce enthusiastically. Many weeds seem to compensate for their ungracious appearance with an even greater abundance of some special power, adaptability, or reproductive vitality. This means that they don’t need the enticing splendor of a cultivar to engage man or to encourage the birds and the bees to assist them in their procreative mission.

Horseweed, pictured just below is a prime example of a powerfully spreading weed with an ungracious appearance. Horseweed is covered in Q #9, part A, above.

Left: Horseweed flower and seedheads Center: Horseweed topgrowth Right: Horseweed roots and stalks

Some weeds pollinate themselves as well as out-crossing,

Common ragweed, Ambrosia artemisiifolia, (Q#5) has a multiplicity of tiny chartreuse to reddish bells along its spikes that contain male flowers up top where they can catch the wind. The pollen from the upper male flowers float down to fertilize the female flowers waiting below, protected from the wind, on the same spike. Common ragweed will morph the gender of its floral cells to match flower position within the environment. These don’t need to look good to propagate. Horseweed, Conyza Canadensis, "(above)" will certainly not win a beauty contest, even in flattering light, and it too can self-pollinate.

Wind pollinates others.

Crabgrass, Digitaria, (Q#1) forms so many seeds on its spiky flower stalks, that it needs no help in propagation. When the wind blows, or the mower mows, each of the many nubbly flowers along the stalk forms tiny seeds that land everywhere and sprout several generations in a season.

Roots lead the reproductive way for other weeds

Roundleaf greenbriar, Smilax rotundifolia, (Q#3) possesses strong prickly root systems and the ability to clone itself and grow from even tiny fragments left behind. It relies less on seed spread, though it does also reproduce via seeds. Critters eat its ripe berries that contain seeds and pass the seeds along to germinate, usually with added fertilizer (scat). But it reproduces by seed less efficiently and less frequently. It takes a careful eye to spot its flowers and berries which grow much smaller than its prodigious roots. It takes little to notice its profusion of sharp prickles, its massive impenetrable vines, or its steel cable sized prickly roots.

Some weeds evolved exploding seed pods that disperse seeds widely,

Like many members of the mustard family such as Hairy bittercress, Cardamine hirsuta (Q#2).

Other weeds amp up the explosion with seeds that screw themselves into the soil,

Like Redstem filaree, Erodium cicutarium, (Q#2). It does have pretty flowers, but they are smaller, relative to the sprawl of its foliage, than the flowers of its cultivated cousins in the Geranium family.

Others hitch rides on passersby

Either via hooks on seeds, sticky covering on seeds, or prickly seedcases that stick onto fur, into hooves, or onto socks, to help weeds become fruitful and multiply elsewhere, such as Devil’s beggarticks, Bidens frondosa, or Common burdock, Arctium minus (Q#2), neither of which form scrumptious big flowers.

EXCEPT

Lots of weeds have big attractive flowers as well as prodigious reproductive prowess. Like those dangerous wealthy playboys, vamps, movie stars, or handsome and powerful politicians, these beauties seduce both pollinators (and people) in meeting their objectives, leaving behind the destruction of nearby plants (or spouses) in their wake. For example, the pretty Japanese knotweed, Fallopia japonica, (Q#1) started as an ornamental before taking over as a weed. So did Japanese honeysuckle, Lonicera, (Q#3) and Kudzu, Puereria lobata (Q#2).

Other weeds display numbers of gorgeous, large flowers like Chicory, Cichorium intybus, or Bouncing bet, Saponaria officinalis.

How can Chicory, Cichorium intybus with its pretty sky blue wildflowers generate problems?

In Colorado, South Dakota, Wisconsin and Minnesota, where it competes with desired crops, it ranks as either “noxious” or “troublesome”. Its deep taproots anchor it well, help it tolerate drought to spread widely, and can penetrate even barren compacted roadside soils, where little else can compete. Like other Composite flowers, a single plant’s multiple fertile florets produce thousands of durable, traveling seeds.

To its credit, it also solves many edible, potable, industrial, and health problems. As far back as ancient Arabia and Egypt, Chicory provided a caffeine-free coffee substitute or flavorful addition to coffee, and a choice edible green. It has had time to naturalize here, predators know where to find it, and it balances within the ecosystem. It signals an alkaline soil low in humus and calcium and it keeps sunny, dry, compacted, airless soil near cement from eroding. If left in this low calcium soil, its deep taproot brings calcium and other nutrients up to feed the soil surface. As they delve, taproots loosen and aerate compacted earth and prevent erosion, and the lovely colors of its flowers brighten barren roadside sites.

Left: Chicory has gorgeous flowers Right: Chicory grows in terrible soil and becomes raggedy-looking

Bouncing bet, Saponaria officinalis, with its bouncy beautiful blooms, is a hit in all the wildflower books. Many weed books make no mention of it. Its benefits? Our frugal forbears brought it to the U.S. to use for washing and plumping up wool, for cleaning fine china and delicate lace, to add a foamy head to beer, as an ornamental, as a fragrant cover up of less desirable odors, and as a wonder drug for garden pharmacopeias. By day, butterflies and bees drink the sugary nectar of its dainty pink flowers. By night, moths flock to its sweet clove like scent, released at sundown. It naturalized here and provides little threat to the native ecosystem. When I first saw it adorning neglected sites, I was both enchanted and intrigued. Not only does it prevent erosion in tough soils, but also it adds prettiness to the type of site usually inhabited by less attractive weeds.

It has that weediest of characteristics: the ability to grow where angels fear to tread. It spreads extensively, resists removal and can be toxic. Yet others still plant it or let it be…you decide if its benefits for you outweigh its risks. I prefer to use its more cultivated cousins, like Sweet William, that cooperate better in my rich garden soil.