Ornamental · Equisetaceae
Horsetail
Equisetum hyemale
Striking, jointed evergreen stems for a wet spot, but only ever inside a container that stops it running wild.
Full sun
Every 1–3 days
USDA 3–11
2–4 ft · 0.6–1.2 m
Overview
Horsetail, also called scouring rush, is one of the oldest plant lineages still growing today, a survivor from the age before flowers. It throws up stiff, jointed, bamboo-like green stems that stay upright year-round and never bear a true leaf or bloom. Instead it spreads by spores from a cone at the stem tip and, far more vigorously, by underground rhizomes.
Gardeners reach for it as a bold vertical accent at the edge of a pond or in a bog bed, where its narrow evergreen stems read almost like living architecture. The gritty, silica-rich stems gave it the old name scouring rush, since people once used them to scrub pots. It asks for almost nothing beyond constant water.
The plant comes with a serious warning on two fronts. Its rhizomes run deep and fast and make it one of the hardest plants to remove once it escapes, so it belongs in a sealed container, never loose ground. It also carries thiaminase, a compound that poisons grazing horses and livestock, which is reason enough to 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, grown inside a solid container or barrier so its rhizomes can't run.
Light
Horsetail grows best in full sun but takes partial sun and even partial shade without complaint. Give it enough light and the stems stand stiff and dense, while deep shade leaves them thin and floppy.
Water
This is a bog plant that wants its roots constantly wet, so water every 1 to 3 days and never let the soil dry out. It is happiest at a pond edge or in a pot standing in shallow water up to about 4 inches (10 cm) deep.
Soil
Plant it in wet to constantly moist, boggy soil. It isn't fussy about texture and grows in clay, loam, or sand, and it even tolerates standing water, which suits its life at the margins of ponds and streams.
Temperature
Few plants are tougher. Horsetail shrugs off the cold down to -40°F (-40°C) and handles heat to around 100°F (38°C), which is why it thrives across such a wide range of climates.
Humidity
It likes high humidity, a natural fit for the damp, waterside spots where it grows. Keep the soil saturated and the air around a pond or bog will take care of the rest.
Feeding
This is an undemanding plant that needs little to no fertilizer. If it's confined to a pot, a light, balanced feed in spring is plenty; in the ground it gets by with nothing at all.
Pruning
Cut old or damaged stems back to the base in late winter or early spring to tidy the clump. Snip off the spore cones before they ripen if you want to hold back any spread, and never compost the trimmings or stray rhizome bits.
Repotting
Repot every 1 to 2 years to refresh the soil and, just as important, to keep the aggressive rhizomes penned in. If you see a dense mat of roots filling the pot or stems climbing over the rim, it's time.
Size & spacing
Stems stand 2 to 4 feet (61 to 122 cm) tall, and a stand will run 1 to 6 feet (30 to 183 cm) wide if you let it. That spreading habit is exactly 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 it lives outdoors year-round across most of the country. Plant it in spring once the soil has warmed, and only ever into a fully contained pot or a bottomless barrier. It doesn't flower or set a crop; it pushes spore cones 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. Your real challenge is keeping it where you put it, so the warnings below lean toward containing its spread far more than nursing a sick plant.
Stems popping up far from where you planted them
This is the plant's defining flaw, an aggressive, deep-running rhizome network that can travel several feet down and outward to form colonies and slip out of ponds into surrounding wet ground. Any fragment left behind resprouts, so digging and herbicides rarely clear it. Grow it only in a solid pot or a bottomless barrier, cut back escaping stems on sight, and destroy every scrap of rhizome you dig out.
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 flopping, yellowing, or growing thin and sparse
Weak, floppy growth almost always means the soil dried out, because horsetail wants constant moisture and sulks the moment its roots go dry. Deep shade thins it out too. Keep the soil saturated or stand the pot in water, and move it somewhere brighter, anywhere from full sun to part shade.
Fix:
- Keep soil constantly wet or stand the pot in water
- Move to a site with more sun (full sun to part shade)
Toxicity
Treat this plant with respect. It is genuinely poisonous to horses and livestock, because the thiaminase it carries destroys vitamin B1 and brings on weakness, staggering, and worse, and it stays toxic even after drying in hay. It isn't a major poisoning risk to cats and dogs, but it isn't edible for anyone, so keep it away from pastures, grazing animals, and curious mouths.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds · People
Cats Caution
Not a known poisoning risk for cats, and it isn't on the ASPCA toxic list for them. Still, it isn't food, so discourage a cat from chewing the stiff stems.
Dogs Caution
Dogs aren't listed as at real risk, and the plant isn't flagged toxic to them. A curious chewer may get a mild stomach upset from the gritty, silica-rich stems, so it's best kept off the menu.
Horses Toxic
Horses are the most at risk. The thiaminase in horsetail strips out vitamin B1, and a horse eating enough, fresh or dried in hay, loses weight and grows weak, then starts staggering and trembling, with convulsions and death in the worst cases.
Rabbits Caution
The same thiaminase that harms larger grazers is a reason to keep horsetail out of a rabbit's diet. Don't offer it, and pull any that creeps into a grazing run.
Livestock Toxic
Cattle, sheep, and other grazing stock develop the same vitamin B1 deficiency, called equisetosis. Watch for weakness, staggering, and poor coordination, with death possible in severe cases, and remember that contaminated hay stays dangerous long after it dries.
Birds Caution
There's little clear evidence either way for birds, so treat it as off-limits rather than safe. Keep poultry and pet birds away from the foliage.
People Caution
This isn't an edible plant, and its thiaminase works against vitamin B1 in people too. Skip casual nibbling or home remedies, and keep children from chewing the stems.
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 conversations about horsetail.
Equisetum giganteum (giant horsetail)
This South American giant of the genus towers well beyond 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, which is a blessing and a curse. The same readiness to root from a scrap of rhizome is what makes it spread out of bounds, so propagate it only with containment firmly in mind.
DivisionEasy
Spring · A few weeks to a season
Divide the rhizome clumps in spring and the pieces take hold within a few weeks to a season, with even tiny fragments rooting 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 don't want.
Myths
Horsetail is an easy, harmless little ornamental for the garden.
It is one of the hardest plants to ever get rid of, spreading by deep rhizomes that escape ponds and shrug off herbicides, and the thiaminase it carries poisons grazing horses and livestock. Confine it to a container and keep it far from pastures.