Vegetable · Brassicaceae
Watercress
Nasturtium officinale
Give it cool, clean, moving water, and watercress hands you a peppery harvest from spring right through fall.
Full sun
Every 1–3 days
32–77°F · 0–25°C
50–60 days
Overview
Watercress is a fast-growing aquatic green with a bright, peppery bite that wakes up a salad or a sandwich. It belongs to the mustard family alongside cabbage and radish, not the climbing garden nasturtium it's often confused with, and it grows wild along the edges of cool, clean streams across much of the temperate world.
What sets it apart from most kitchen greens is where it lives. The roots want to be wet all the time, ideally in flowing spring water, and the plant will happily root straight into a muddy bank or a pot standing in a tray of water. Keep the water cool and moving and watercress grows almost faster than you can pick it.
It earns its place as one of the easiest edibles to keep going. Pinch the shoots often, and the plant bushes out and stays tender. Let the water warm up or sit still, though, and it bolts, turns bitter, and thins out fast.
Care
The short version: cool, clean water around the roots at all times, full sun to part shade, and regular picking to keep the leaves tender and stop it from flowering.
Light
Watercress takes full sun to partial shade. Plenty of sun gives you the heaviest growth, but a bit of afternoon shade pays off in summer by keeping the water and the leaves cooler.
Water
This is the part that makes or breaks it. The roots must stay submerged or in constantly saturated soil, never drying out for a moment. Cool, clean, flowing or spring water is ideal; in a container, stand the pot in a tray of water and refresh it every 1 to 3 days to keep it cool, clean, and full of oxygen.
Soil
Grow it in rich, mucky loam at a water's edge, or a soil-filled pot standing in water. It handles a wide pH band from 6.5 to 8.0, leaning toward the neutral-to-alkaline side that suits its native limestone streams.
Temperature
Watercress is a cool-water plant that runs from about 32°F to 77°F (0°C to 25°C). It shrugs off frost but bolts and turns bitter once the water warms much past the top of that range, so summer shade and cool water keep it going.
Humidity
Being an aquatic plant, it likes the air humid, from 70% up to nearly 100%. Standing water around the roots usually keeps the air moist enough on its own, so this rarely needs any thought.
Feeding
In clean flowing water the plant usually feeds itself, so you can skip fertilizer entirely. In a container, give a dilute balanced liquid feed monthly through spring and summer, when the still water can't supply enough on its own.
Pruning
Pinch and harvest the shoot tips often to push bushy, tender growth. The moment flower stalks appear, snip them out, since flowering turns the leaves bitter and signals the plant to wind down.
Repotting
Lift and divide the mat about once a year, or sooner if the stems crowd together and new growth slows. Crammed stems creeping out of the tray are your cue that it's time to give it fresh room.
Size & spacing
Plants stay low, running 4 to 20 inches (10 to 50 cm) tall, but they spread sideways into a mat 12 to 35 inches (30 to 90 cm) across. Give that spread room to roam, or thin it so the water keeps moving through.
When to plant
Watercress is a cool-season green that grows hard in spring and fall and sulks in summer heat. Surface-sow seed in late winter to early spring, set young plants out once hard frost has passed, and pick the leaves from spring through fall, 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 watercress trouble traces back to the water or the weather. Warm, still water and summer heat cause the bulk of it, and the leaves tell you early. Match what you see below and fix the conditions before the whole mat goes downhill.
Pale, yellowing leaves on a tired-looking mat
Warm, still water sits at the root of this. When the water stops moving it loses oxygen and warms up, and the older leaves go pale first. Refresh or circulate the water to keep it cool, move the plant into partial shade through the summer heat, and feed a dilute balanced fertilizer if you grow it 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
Flower stalks shoot up and the leaves turn harsh and bitter
This is bolting, and heat is what triggers it. Once the water climbs past about 75°F (24°C), the plant throws up flower stalks, the leaves shrink, and the peppery bite turns into something downright harsh. Pinch out the flowering stems, drop the plant into shade with cooler water, and if summer has the upper hand, start fresh from stem cuttings when the weather cools.
Fix:
- Harvest and pinch out flowering stems
- Provide shade and cooler water
- Restart from stem cuttings in the cooler season
Curled leaves with clustered bugs or tiny shot-holes
Two pests do most of this damage. Aphids gather on the leaf undersides and twist the new growth, while flea beetles chew the small round holes that pepper a leaf like buckshot. Knock both off with a strong jet of water and cut away any shoots that are badly chewed.
Fix:
- Dislodge pests with a strong jet of water
- Remove and discard heavily infested shoots
Toxicity
Good news on this one: watercress is a food crop, not a hazard. It's safe for cats, dogs, horses, rabbits, livestock, birds, and people alike, with no toxin in any part of the plant. The only real caution is for people, and it's about where the cress grew rather than the plant itself.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Watercress isn't toxic to cats. A curious nibble does no harm, though most cats won't bother with the peppery leaves.
Dogs None
Safe for dogs, leaves and stems alike. A dog that gobbles a big mouthful might get a mild bout of gas, but nothing more.
Horses None
Horses can graze it without trouble. The sharp mustard tang usually keeps them from eating much of it anyway.
Rabbits Safe
Rabbits can eat watercress as part of a mixed green diet. Introduce it slowly, the way you would any new leafy vegetable, so their gut adjusts.
Livestock Safe
Cattle, goats, and sheep can browse watercress safely. It carries no toxin that would 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: 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'll grow is simply the wild species, but a couple of named types are worth knowing.
Improved Broad Leaved
A cultivated strain bred for bigger, broader leaves and a heavier harvest than the wild plant gives you.
Nasturtium microphyllum (one-row, small-leaved watercress)
A close cousin with smaller leaves and single-rowed seeds that readily crosses with true watercress where the two grow side by side.
How to propagate
Watercress multiplies so readily it's almost hard to stop, whether you root a few cuttings in a glass of water or scatter seed on damp ground.
Stem cuttingsEasy
Any time during active growth, best in spring or fall · 1 to 2 weeks
This is the quickest way to start watercress, and you can do it any time the plant is growing, though spring and fall give the best results. 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. They root at the nodes within 1 to 2 weeks and you're off.
SeedEasy
Spring, in cool moist conditions · 2 to 3 weeks to germinate and establish
Seed works well in the cool, damp weather of spring. Scatter the tiny seeds on the surface of a constantly moist medium rather than burying them, since they need light and must never dry out. Give them 2 to 3 weeks in cool temperatures to sprout and find their feet.
Myths
Wild watercress is always safe to eat raw straight from the stream.
Cress pulled from water grazed by livestock can carry liver fluke larvae and other waterborne bugs you can't see. Cook wild-harvested cress, or grow your own in clean water, before you eat any of it raw.
Edible watercress is the same plant as the ornamental garden nasturtium.
They share a peppery taste and a common name, but that's where it ends. Edible watercress is Nasturtium officinale in the mustard family, while the climbing garden nasturtium is Tropaeolum majus, a completely separate genus.
Watercress needs deep running water and can't be grown at home.
Flowing spring water is the ideal, but it isn't a must. A pot of rich soil standing in a tray of water kept wet and refreshed grows you a steady supply right on a windowsill or patio.