Horseweed (Erigeron canadensis)

Butterweed, Canadian Horseweed, Colstail, Horseweed, Horse Weed, Marestail

Horseweed is a North American herbaceous annual plant with a hairy stem, numerous pointed leaves, and waxy inflorescence. It has been naturalized in Eurasia and Australia, where it is a common weed in urban and agricultural regions. Horseweed can be used in a survival situation to start a friction fire.

I. Appearance and Characteristics 

Erigeron canadensis (synonym Conyza canadensis) is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia. Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail, and butterweed. 

It has spread to inhabited areas of most of the temperate zone of Asia, Europe, and Australia. It is found in Britain from northern Scotland to Cornwall, growing as a weed of arable land and man-made environments. It is considered invasive in China.

It was the first weed to have developed glyphosate resistance, reported in 2001 from Delaware.

If you observe the plant closely, you discover that its stalk has many branches and the branches all grow upwards. What makes it magical is that each branch is covered with short hairs. When the sun shines on it, the shadow cast on the ground looks like a horse tail. So, it is called mare’s tail or horseweed.

Erigeron canadensis is an annual, herbaceous plant growing to 1.5 metres (5 feet) tall, with sparsely hairy stems. The leaves are unstalked, slender, 2–10 centimetres (0.8–3.9 inches) long, and up to 1 cm (0.4 in) wide, with a coarsely toothed margin. They grow in an alternate spiral up the stem, and the lower ones wither early. The flower heads are produced in dense inflorescences and are 1 cm (0.4 in) in diameter. Each individual flower has a ring of white or pale purple ray florets and a centre of yellow disc florets. The fruit is a cypsela tipped with dirty white down.

Erigeron canadensis can easily be confused with Erigeron sumatrensis, which may grow to a height of 2 m (6.6 ft), and the more hairy Erigeron bonariensis, which does not exceed 1 m (3.3 ft). E. canadensis is distinguished by bracts that have a brownish inner surface with no red dot at the tip, and are free (or nearly free) of the hairs found on the bracts of the other species.

This is a plant with amazing seed production. One plant can produce over 200,000 seeds that can be windblown up to a quarter of a mile

Horseweed has a fibrous root system and a shallow taproot. Depending on the soil conditions, you may be able to hand remove small plants. The proper use of mulch in ornamental plant areas can also effectively reduce this weed.

Horseweed is a common landscape and agricultural weed, mainly found on undisturbed lands. It is infamous for being the first weed to develop resistance to the widely used herbicide, glyphosate. What’s more, the germination time is flexible, so horseweed can emerge in all seasons except winter, and the seeds spread efficiently like dandelion seeds. Horseweed has been spreading outside of its native range for centuries and can now be found in grasslands, fields, and many disturbed areas in Europe, Asia, Australia, northern Africa, and tropical parts of the Americas. It is considered an agricultural weed both in its native and naturalized range.

It can be found in fields, meadows, and gardens throughout its native range. Horseweed infestations (specifically of 105 plants per 10 ft²) have reduced soybean yields by as much as 83%, with one estimate claiming it can reduce yields by up to 90%. Severe infestations have reduced sugar beet yields by 64%.

It is an especially problematic weed in no-till agriculture, as it is often resistant to glyphosate and other herbicides. Farmers are advised to include 2,4-D or dicamba in a burndown application prior to planting to control horseweed.

In certain people, skin contact with the plant might result in dermatitis. So, it’s advisable to wear gloves while handling the plant. Also, keep it out of the reach of children and pets.

II. How to Grow and Care

Light And Temperature

Horseweed grows easily almost anywhere in North America but grows rapidly in warm, dry locations.

It can tolerate direct afternoon sunlight outdoors, especially when grown in a humid region.

When grown indoors, avoid placing it near a south-facing or west-facing window getting lots of direct afternoon sunlight.

Grow the plant in full sun when grown outdoors.

Watering And Feeding

  • Water occasionally, but avoid overwatering. 
  • The plant can tolerate drought and prefers slightly drier conditions.
  • Fertilizer isn’t needed. 
  • The plant will likely reach its full height within one or two years with or without plant food.
  • During the winter, the plant only needs water when the lower leaves start to wither away.

Soil And Transplanting

  • Although horseweed can grow in a variety of soil types, it thrives in rich, loamy soil.
  • Mix equal parts sand, clay, and organic material, or use regular soil that has been improved with some perlite to create loamy soil.
  • Unless the plant begins to take over a significant portion of a garden or yard, it is not necessary to transplant it.
  • It can rapidly spread and outcompete other vegetation.
  • Transplant the plant in the spring, before its rapid growth begins in the summer, to save it.

Planting Instructions

  • After the flowers have faded, the seeds can be collected directly from the plant.
  • If bristly seeds develop, just put a plastic bag over them until they’re dry.
  • After the seeds have dried, you should prune any remaining branches and put them in an envelope for the winter.
  • Plan on planting the seeds in a starter tray filled with regular potting soil the following spring.
  • Don’t let the soil dry out as the seedlings emerge.
  • Plants should be moved to their permanent locations once they develop leaves.

Grooming

To manage growth, trim the plant back at any time of the year.

Transplanting 

Transplant horseweed ideally during the balmy window of mid-spring to early summer. Choose a well-draining location with adequate sunlight. For best results, acclimate seedlings to outdoor conditions and keep soil evenly moist.

Propagation

Propagate by division, seeds, or cuttings. 

  • Harvest seeds directly from the plant after the flowers fade. 
  • When the bristly seeds appear, cover them in plastic and wait for them to dry.
  • After the seeds dry, trim the connected branches and store seeds overwinter in an envelope. 
  • Sow the seeds the following spring in standard potting soil in a starter tray.
  • Keep the soil moist as the seedlings appear. 
  • When leaves start to appear, transplant the plants to permanent homes. 
  • It’s also possible to sow the seeds directly in the soil.

To grow from cuttings or division

  • Remove a healthy branch from the plant or dig the plant up and divide it at the base
  • Dip cuttings in the rooting hormone.
  • Plant the divided plants or cuttings in regular potting soil or directly in the garden bed. 
  • Keep moist as the young plants take root and new growth appears but avoid overwatering.

Pests and Diseases

  • When grown indoors, the plant tends to attract spider mites. 
  • These pests may also appear on outdoor plants in dry regions.
  • Spraying the plant with cold water is a common treatment but may damage the thin stems of the horseweed plant. 
  • To save the plant, use a miticide or propagate parts of the plant not yet infested.
  • Along with pests and diseases, consider where it’s grown. 

In Ohio, the plant is considered a noxious weed. 

Infestations of the plant have reduced soybean field yields and other harvests in the region.

While it’s a weed, Erigeron canadensis isn’t considered invasive in other regions.

  • Keeping the plant away from children and pets is also a good idea. 
  • The foliage may irritate skin.
  • If ingested, parts of the plant may also cause gastrointestinal distress. 
  • In the wild, horses know to avoid the plant due to its bitter taste.

III. Uses and Benefits 

Horseweed isn’t a commonly grown houseplant as it’s often thought of as a weed. However, some people enjoy growing it in the kitchen as an herbal plant. 

Despite the mild toxicity, the dried leaves provide a flavor comparable to tarragon. When grown outdoors, horseweed can help attract butterflies, bees, and insect pollinators. It also appears in the wild growing near pastures, fences, abandoned fields, construction sites, and anywhere with exposed topsoil.

Horseweed is drought-tolerant and can be planted in areas where erosion control is needed.

A leaf decoction from this plant is used to cure a sore throat or dysentery.

The Zuni people insert the crushed flowers of E. canadensis var. canadensis into the nostrils to cause sneezing, relieving rhinitis. Other Native Americans have used a preparation of the plant’s leaves to treat sore throat and dysentery. A tincture can be made from the dried flowering tops of the plants.

Horseweed is a preferable material for use in the hand drill-method of making friction fire.

Horseweed (Erigeron canadensis) Details

Common name Butterweed, Canadian Horseweed, Colstail, Horseweed, Horse Weed, Marestail
Botanical name Erigeron canadensis
Plant type Annual
Growth rate Medium
Height 0 ft. 6 in. - 7 ft. 0 in.
Width 0 ft. 6 in. - 7 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Flower color Cream/Tan
Leaf color Green