Ornamental · Equisetaceae
Horsetail
Equisetum hyemale
Ridged, jointed, dark-green evergreen stems for a wet spot, held only inside a container so they cannot run wild.
Full sun
Every 1–3 days
USDA 3–11
2–4 ft · 0.6–1.2 m
Overview
Horsetail, also called scouring rush, throws up stiff, jointed, bamboo-like green stems that stand straight and unbending, ringed at each joint by a dark band where one hollow segment meets the next. The stems carry no true leaf and no bloom, just bare green rods that hold their color and their upright poise right through the year. It belongs to one of the oldest plant lineages still alive, older than the flowering plants.
Run a finger along a stem and it feels gritty and rough, its surface stiffened with silica that once let people scrub pots with it, which is how it earned the name scouring rush. In spring to summer a firm, cone-like tip, the strobilus, forms at the end of a stem and releases the spores it breeds from. Below ground, dark rhizomes spread far more freely than the spores ever do.
Those underground stems are the catch. They run deep and fast, which makes horsetail one of the hardest plants to remove once it escapes, so it belongs in a sealed container rather than open ground. The green stems also hold thiaminase, a compound that poisons grazing horses and livestock, so keep it well away from pastures.
Care
The short version: full sun to part shade and soil that never dries out, ideally a pot standing in water, with the plant grown inside a solid container or barrier so its rhizomes can't run.
Light
Horsetail grows best in full sun, though it takes partial sun and even partial shade. Plenty of light keeps the green rods stiff and packed close, while deep shade leaves them thin and prone to bend.
Water
This bog plant wants its roots constantly wet, so water every 1 to 3 days and never let the soil dry out. It stands happily at a pond edge, or in a pot set in shallow water up to about 4 inches (10 cm) deep.
Soil
Plant it in wet to constantly moist, boggy soil. It shows no fuss over texture, rooting in clay, loam, or sand, and it even holds up in standing water, a fit for a plant born at the margins of ponds and streams.
Temperature
Its hardiness is striking. Horsetail shrugs off cold to -40°F (-40°C) and takes heat to around 100°F (38°C), which is why the green stems persist across such a wide sweep of climates.
Humidity
It favors high humidity, a natural match for the damp, waterside spots where it grows. Keep the soil saturated and the moist air around a pond or bog supplies the rest.
Feeding
This is an undemanding plant that needs little to no fertilizer. A potted specimen takes a light balanced feed in spring; in the ground the green stems get by on nothing at all.
Pruning
Cut old or damaged stems to the base in late winter or early spring to freshen the clump. Snip off the cone-like spore tips before they ripen to hold back any spread, and never compost the trimmings or stray rhizome pieces.
Repotting
Repot every 1 to 2 years to refresh the soil and keep the aggressive rhizomes penned in. A dense mat of pale roots filling the pot, or stems climbing over the rim, tells you it is time.
Size & spacing
The stems stand 2 to 4 feet (61 to 122 cm) tall, straight and rod-like, and a stand will spread 1 to 6 feet (30 to 183 cm) wide if let go. That reach is why it belongs in a contained pot or barrier rather than open ground.
When to plant
Horsetail is a tough perennial hardy from zone 3 to 11, so its green stems stand outdoors year-round across most of the country. Plant it in spring once the soil has warmed, and only into a fully contained pot or a bottomless barrier. It bears no flower and no crop; instead it raises cone-tipped spore stems from spring into summer.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: Spring, once the soil has warmed; site only in a fully contained pot or bottomless barrier
- Harvest: Non-flowering; produces spores in a cone-like tip (strobilus) in spring to summer
Hardiness
USDA hardiness zones: 3–11
Temperature: down to -40°C
Troubleshooting
Horsetail rarely struggles to grow. The real challenge is keeping its far-running stems where you put them, so the notes below lean toward containing its spread far more than nursing a sick plant.
Fresh green stems piercing the soil far from the clump
Beneath the tidy upright stems runs the plant's true engine, an aggressive network of dark, deep rhizomes that snakes several feet down and outward, knits into colonies, and pushes out of a pond into the wet soil beyond. Snap one and every piece resprouts, so digging and herbicides barely dent it. Pen it in a solid pot or bottomless barrier, sever escaping stems as they spear up, and destroy each black rhizome fragment you turn out of the ground.
Fix:
- Never plant loose in open ground; grow only in a solid pot with no drainage to the soil, or in a bottomless barrier sunk into the bed
- Repeatedly cut or pull emerging stems to starve the rhizomes over time
- Remove and destroy (do not compost) every rhizome fragment when digging out an established stand
Stems bending over, yellowing, or growing sparse
When the stiff green rods lose their backbone and lean into a floppy, yellowing, thin stand, the trouble is nearly always a root zone gone dry, since horsetail wants steady moisture and slumps the moment its roots dry out. Deep shade leaves the clump sparse too. Saturate the soil or stand the pot in water, and give it a brighter spot from full sun to part shade, and the green rods stiffen and thicken again.
Fix:
- Keep soil constantly wet or stand the pot in water
- Move to a site with more sun (full sun to part shade)
Toxicity
Look past the handsome green rods and treat this plant with respect. It is genuinely poisonous to horses and livestock, because the thiaminase in its stems destroys vitamin B1 and brings on weakness, staggering, and worse, and it stays toxic even after the stems dry into hay. It is no major risk to cats and dogs, but it is edible for no one, so keep it away from pastures, grazing animals, and curious mouths.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
Horsetail is no known poisoning risk to cats and stays off the ASPCA toxic list for them. The stems are stiff and gritty rather than food, so keep a curious cat from gnawing on them.
Dogs Caution
Dogs are not flagged as truly at risk, and the plant is not listed as toxic to them. Those gritty, silica-rich stems can leave a chewer with a mild stomach upset, so it is best kept out of reach.
Horses Toxic
Horses are the most at risk. The thiaminase in horsetail strips out vitamin B1, and a horse that eats enough, whether the fresh green stems or dried pieces in hay, loses weight and weakens, then begins staggering and trembling, with convulsions and death in the worst cases.
Rabbits Caution
The same thiaminase that harms larger grazers keeps horsetail out of a rabbit's diet. Offer none of the stems, and pull any that creep into a grazing run.
Livestock Toxic
Cattle, sheep, and other grazing stock develop the same vitamin B1 deficiency, called equisetosis. Weakness, staggering, and poor coordination appear, with death possible in severe cases, and even the dried, brittle stems in contaminated hay stay dangerous long after they dry.
Birds Caution
Clear evidence for birds is thin either way, so the green stems are best treated as off-limits rather than safe. Keep poultry and pet birds away from the foliage.
People Caution
Horsetail is no edible plant, and its thiaminase works against vitamin B1 in people too. Skip any nibbling of the stems or home remedies, and keep children from chewing them.
Safe to handle and not a significant pet toxin, but keep this plant well away from pastures, grazing horses, and livestock, and never let it contaminate hay; even dried plants in hay retain the thiaminase toxin.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
Poison Control: (800) 222-1222
Canada
Poison Centres: 1-844-764-7669
Varieties
The genus holds dozens of species, but a few turn up most often in gardens and in talk about horsetail.
Equisetum giganteum (giant horsetail)
The towering South American member of the genus, it rises far taller than the temperate scouring rushes.
Equisetum arvense (field horsetail)
A smaller, branching weed of disturbed ground, it carries the same thiaminase that makes it toxic to horses and livestock.
Equisetum scirpoides (dwarf scouring rush)
The miniature of the group, it forms low clumps of slender, wiry, often curly stems only about a foot tall.
How to propagate
Horsetail multiplies all too easily. The same readiness of its rhizomes to root from a single dark scrap is what sends it spreading out of bounds, so propagate it only with containment firmly in mind.
DivisionEasy
Spring · A few weeks to a season
Split the dark rhizome clumps in spring and the pieces take hold within a few weeks to a season, with even tiny fragments sending up new green stems on their own. That eager rooting is exactly what makes the plant so invasive. Always replant into a fully contained pot or barrier and destroy any fragments you do not want.
Myths
Horsetail is an easy, harmless little ornamental for the garden.
It is one of the hardest plants to ever clear, driving deep rhizomes that break out of ponds and shrug off herbicides, and the thiaminase packed in its stems poisons grazing horses and livestock. Hold it in a container and keep it far from pastures.