Vegetable · Brassicaceae
Watercress
Nasturtium officinale
Set in cool, clean, moving water, watercress spreads a low mat of tender, peppery leaves from spring through fall.
Full sun
Every 1–3 days
32–77°F · 0–25°C
50–60 days
Overview
Watercress grows as a low sprawl of tender green leaves carried on trailing stems, each leaf sharp and peppery on the tongue. It sits in the mustard family with cabbage and radish, not the climbing garden nasturtium it is often mistaken for. In the wild it threads along the edges of cool, clean streams across much of the temperate world.
Its stems are the plant's defining feature: they trail and creep, rooting at the nodes wherever they touch wet ground, and knit together into a dense bankside or floating mat. The roots stay wet at all times, best of all in flowing spring water, though the plant takes just as readily to a muddy bank or a pot standing in a tray of water.
Kept cool and picked often, the mat stays low and thick with soft leaves. Come warm weather it changes character, sending up thin flowering stalks topped with small white cross-shaped flowers, and the leaves shrink and sharpen as it does. That shift from leafy mat to flower stalk is the plant telling you the water has grown too warm.
Care
The short version: cool, clean water around the roots at all times, full sun to part shade, and frequent picking to keep the leaves tender and hold back the flower stalks.
Light
Watercress takes full sun to partial shade. Full sun draws out the densest, deepest-green mat, while a little afternoon shade in summer keeps the water and the leaves cooler.
Water
Water is everything to this plant. The roots stay submerged or in constantly saturated soil, never drying out for a moment. Cool, clean, flowing or spring water is ideal, and in a container the pot stands in a tray of water, refreshed every 1 to 3 days to keep it cool, clean, and oxygenated.
Soil
Its roots run into rich, mucky loam at a water's edge, or a soil-filled pot standing in water. The pH ranges from 6.5 to 8.0, tilting toward the neutral-to-alkaline side of the limestone streams it comes from.
Temperature
Watercress is a cool-water plant, at ease from 32°F to 77°F (0°C to 25°C). It takes frost without harm, but once the water climbs past that range the leaves shrink, sharpen, and bolt, so summer shade and cool water hold it steady.
Humidity
As an aquatic plant it sits in humid air, from 70% up to nearly 100%. The standing water around its roots keeps the surrounding air moist on its own, so the leaves rarely want for humidity.
Feeding
In clean flowing water the leaves feed themselves and need no fertilizer. In a container, a dilute balanced liquid feed monthly through spring and summer keeps the foliage full, since still water cannot supply enough on its own.
Pruning
Pinching and harvesting the shoot tips keeps the mat low, dense, and tender-leaved. Thin flowering stalks are snipped out as they rise, since flowering shrinks the leaves and turns them bitter.
Repotting
The mat is lifted and divided about once a year, or sooner once the stems crowd into a tangle and new growth slows. Stems creeping over the rim of the tray show the plant has filled its space.
Size & spacing
The plant stays low at 4 to 20 inches (10 to 50 cm) tall, but its stems fan out into a mat 12 to 35 inches (30 to 90 cm) across. Give that spreading mat room, or thin it so water still moves between the stems.
When to plant
Watercress is a cool-season green that grows lush in spring and fall and struggles in summer heat. Surface-sow the seed in late winter to early spring, set young plants out once hard frost has passed, and pick the leaves from spring through fall, or year-round where the water stays cool and moving.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Late winter to early spring, surface-sown on constantly moist medium
- Plant: Spring after danger of hard frost, or fall in mild-winter regions
- Harvest: Harvest leaves spring through fall (year-round in mild flowing water); small white cross-shaped flowers appear late spring to summer
Hardiness
USDA hardiness zones: 4–10
Temperature: down to -34°C
Troubleshooting
Most of what goes wrong shows first in the leaves, and most of it comes back to the water or the weather. Warm, still water and summer heat drive the bulk of it. Match the look of your plant below and correct the conditions before the whole mat declines.
Older leaves fading to pale, washed-out yellow
Behind the fading color is almost always warm, still water. As the water stops moving it loses oxygen and warms, and the oldest leaves lose their green first. Refresh or circulate the water to cool it, move the plant into partial shade through the summer heat, and feed a dilute balanced fertilizer where it grows in a container.
Fix:
- Refresh or circulate the water to keep it cool and oxygenated
- Move to partial shade during summer heat
- Apply a dilute balanced fertilizer when grown in containers
Thin flower stalks rise and the leaves shrink and sharpen
This is bolting, triggered by heat. Once the water warms past about 75°F (24°C), the plant pushes up thin flower stalks, the leaves grow small, and the peppery bite hardens into a harsh edge. Pinch out the flowering stems, move the plant into shade with cooler water, and, where summer wins, restart from stem cuttings once the weather cools.
Fix:
- Harvest and pinch out flowering stems
- Provide shade and cooler water
- Restart from stem cuttings in the cooler season
Twisted new leaves and leaves peppered with tiny round holes
Two pests leave their mark on the foliage. Aphids crowd the undersides of the leaves and curl the soft new growth, while flea beetles chew the small round holes that stipple a leaf like buckshot. A strong jet of water sweeps both away, and the worst-chewed shoots are cut off.
Fix:
- Dislodge pests with a strong jet of water
- Remove and discard heavily infested shoots
Toxicity
Watercress is a food crop, not a hazard. It is safe for cats, dogs, horses, rabbits, livestock, birds, and people, with no toxin in any leaf or stem. The single caution is for people, and it turns on where the cress grew rather than the plant itself.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Watercress is not toxic to cats. A curious nibble of the peppery leaves does no harm, and most cats turn away from the sharp taste anyway.
Dogs None
It is safe for dogs, leaves and stems alike. A dog that swallows a big mouthful may get a little harmless gas, and nothing worse.
Horses None
Horses can graze it without harm. The sharp mustard tang of the leaves usually keeps them from eating much of it.
Rabbits Safe
Rabbits can eat watercress as part of a mixed green diet. Introduce the leaves slowly, as with any new green, so the gut adjusts.
Livestock Safe
Cattle, goats, and sheep can browse watercress safely, since the plant holds no toxin to harm grazing stock.
Birds Safe
Backyard hens and other birds peck at the tender leaves with no ill effect, and the greens add a little variety to their feed.
People Safe
Watercress is a nutritious salad green, eaten raw or cooked. The one real catch is wild plants, since cress foraged from water grazed by livestock can carry liver fluke parasites, so cook wild-harvested cress or grow your own in clean water before eating it raw.
Food-safety note for people (not pet toxicity): wild watercress from water that may be contaminated by grazing livestock can carry liver fluke (Fasciola) larvae and waterborne pathogens. Cook wild-harvested cress or grow it in clean, uncontaminated water before eating it raw.
Varieties
Most watercress you grow is the wild species, but a couple of named types differ in the size of their leaves and seeds.
Improved Broad Leaved
A cultivated strain that carries larger, broader leaves and yields a heavier cut than the wild plant.
Nasturtium microphyllum (one-row, small-leaved watercress)
A close relative marked by smaller leaves and seeds set in a single row, which crosses freely with true watercress wherever the two grow together.
How to propagate
Watercress multiplies with ease, its trailing stems rooting in a glass of water and its fine seed sprouting on damp ground.
Stem cuttingsEasy
Any time during active growth, best in spring or fall · 1 to 2 weeks
The trailing stems root so willingly that cuttings are the fastest start, taken any time in active growth and best in spring or fall. Cut stems about 4 to 6 inches (10 to 15 cm) long and stand them in a glass of water or press them into wet soil. Roots break from the nodes within 1 to 2 weeks.
SeedEasy
Spring, in cool moist conditions · 2 to 3 weeks to germinate and establish
Seed sprouts in the cool, damp weather of spring. The fine seed rests on the surface of a constantly moist medium rather than buried, since it needs light and must never dry out. Under cool temperatures it takes 2 to 3 weeks to germinate and settle in.
Myths
Wild watercress is always safe to eat raw straight from the stream.
Cress lifted from water grazed by livestock can carry liver fluke larvae and other waterborne organisms too small to see. The reliable safeguard is to cook wild-harvested cress, or grow your own in clean water, before eating any of it raw.
Edible watercress is the same plant as the ornamental garden nasturtium.
The two share a peppery taste and a common name and nothing more. Edible watercress is Nasturtium officinale in the mustard family, while the climbing garden nasturtium is Tropaeolum majus, a separate genus entirely.
Watercress needs deep running water and cannot be grown at home.
Flowing spring water is the ideal, but far from a must. A pot of rich soil standing in a tray of water, kept wet and refreshed, grows a steady supply on a windowsill or patio.