For best results, obtain watercress seeds from a well-established seed catalog or local nursery with a reputation for quality plants. Certain varieties of annual, biennial, or perennial watercress are recommended for home gardening. As with any outdoor gardening venture, individuals should take into account the particular challenges of their local growing zones when selecting watercress seeds; in general, watercress varieties tend to be hardy to USDA Zone 9A. Watercress can also be grown as a container or hydroponic plant. As an alternative to starting from seed, watercress can be propagated with the use of cuttings or purchased as transplants.
Watercress seeds are available in many plant varieties. Lepidium sativum, an annual that grows quickly, comes in several varieties including curly cress, garden cress, and peppergrass. Wintercress, a biennial whose scientific name is Barbarea vulgaris, will produce white blooms. A perennial variety, Nasturtium officinale, is also known as big leaf cress or simply watercress.
In a container, watercress seeds should be grown in a soilless potting mix. This type of mix can include elements such as vermiculite or perlite. The preferred pH for successful growth of watercress seeds is a range of 6.0 to 7.5, or mild acidity to mild alkalinity.
Watercress seeds can take up to two weeks to germinate. They need to be watered frequently and will thrive in outdoor environments with running water. Outdoors, watercress tolerates partial shade but prefers full sun. As an indoor container plant, watercress thrives under grow lights and might also do well under normal fluorescent lamps.
The ideal indoor container for growing watercress is a large pot or bucket that can hold several smaller pots. Fill the smaller inside pots with soil mix, and place stones at the bottom to avoid washing away the soil. Place these small pots inside the larger container that is filled with enough water to cover the bottoms of the small pots.
When the soil has become saturated with water, add the seeds. They should be planted about 1 inch (2.5 cm) deep and up to 4 inches (10 cm) apart. Replace the water in the large pot every other day.
One way to propagate watercress without seeds is to take cuttings from purchased fresh watercress. Place the cuttings in water and leave the container in the sun. With luck, roots will sprout from the cuttings. The rooted cuttings can then be transplanted into a container.
Watercress is prized as an addition to salads and other dishes. Its peppery taste and profusion of vitamins and minerals make watercress a popular green. When used as part of a cooked dish, the watercress will have a mild flavor. Make sure to harvest watercress leaves before the plant flowers to avoid a bitter taste.