Low growing and trailing European perennial Nasturtium officinale, a member of the Mustard Family, is naturalized in springs and wet ground in temperate climates.
Though easily grown from seed, it is usually propagated by bits of stem which readily take root in wet soil and need no further attention. Its natural season is from mid-autumn until spring. After its flower buds appear the leaves become too rank in flavor to be edible.
Watercress has many culinary, decorative, and medicinal uses.
Growing the Herb Watercress
It can easily be grown in containers that are dug into the surface of the soil and filled with fresh water on a frequent basis.
It is also easily grown indoors in individual pots that are placed in a tray of water. Start plants with seed by sowing lightly in pots filled with a mix of garden soil, limestone, and organic compost.
Keep moist at all times, keeping the plants in a partially shaded area. As soon as seedlings are large enough to move, in April or May ideally, they can be transplanted to stream or creek banks where they will establish themselves and create a bed that will provide cut watercress every spring and fall.
Outdoors, containers, and hydroponics.
Watercress plants grow to a height of 6 to 24 inches (15 – 60cm).
Watercress plants should be spaced 9 to 12 inches (22 – 30cm) apart.
Preferred pH Range
Watercress will grow in a pH range between 6.0 (mildly acidic) and 7.5 (mildly alkaline) with a preferred pH range between 6.5 and 7.5.
Sow watercress seed indoors in sunny location or under plant grow lights six weeks before last frost. Watercress propagates well through stem cuttings.
Seed Germination Period
Watercress seeds will germinate in soil in approximately 7 to 14 days, but can germinate in as few as 5 or 6 days in dedicated propagation media such as Oasis Rootcubes, Rapid Rooters, or Grodan Stonewool.
Number of Seeds per Gram
There are approximately 5,000 watercress seeds per gram.
Watercress grows well in rich, fertile soil.
Alternative Growing Media
Soilless potting mixes (Pro-Mix, Sunshine Mix, etc.), perlite, vermiculite, rockwool, coco peat, Oasis Rootcubes.
Sun & Lighting Requirements
Watercress grown outdoors prefers full sun but tolerates some shade.
Watercress will grow indoors satisfactorily under standard fluorescent lamps, and exceptionally well under high output T5 fluorescent plant lights, compact fluorescent, or high intensity discharge (metal halide or high pressure sodium) plant growing lights. Keep standard fluorescent lamps between 2 and 4 inches from the tops of the plants, high output and compact fluorescents approximately one foot above the plants, and HID lights between 2 and 4 feet above the plants, depending on wattage.
Have an oscillating fan gently stir seedlings for at least 2 hours per day to stimulate shorter, sturdier, and more natural plant habit.
Perennial. Zones 9a to 11.
Above average water needs. Suitable for bogs and watergardens. Thrives in hydroponics.
Potential Plant Pests and Diseases
Watercress can be susceptible to whitefly and spider mites, but has minimal disease issues.
Grown for aromatic foliage. Requires large amounts of water.