Whereas watercress belongs to the genus Nasturtium, the common nasturtium is quite different. Botanists also give Roripa and Radicula as alternative generic names. Cultivated watercress is known by a variety of common names, such as eker, biller, bilure, rib cress, brown cress, teng tongue, long tails, and well grass.
Watercress is a perennial plant grown for the pungent leaves and young stems, which are widely used for garnishing and in salads. The smooth compound leaves have three to a dozen nearly round 1-inch-wide leaflets. Leaves and stems are partially submerged during growth. It was brought to this country by European immigrants, and now grows wild in running water and flooded places all over the United States. Commercially, it is grown in unshaded shallow pools of flowing clean water.
Watercress does best in a moderately cool climate. Much of the nation's winter supply is grown in Central Florida, but very few home gardeners attempt to produce it.
You may find some success at growing watercress if you have your own stream and know that the water is clean. Set aside a shallow portion, such as on the inside of a bend, for a patch of watercress. The site should be relatively flat with a slight slope away from the water's supply source.
For those without a stream, watercress may still be grown in small quantities. Fashion a plant bed by scooping out a 6-inch deep basin and then lining it with 4 to 6 mil polyethylene. Fill the covered bottom of the basin with about 2 inches of composted soil, peat moss, or other regular potting mix.
Watercress can be grown from either seeds or cuttings. Small plants may be transplanted. Since the seeds are very small, broadcast them thinly over finely prepared compost or potting mix. Then lightly rake to cover the seed. In the final stand, allow 6 inches between plants.
Keep the plant bed moist, but not covered with water. If you are using a shallow portion of a stream bed, you may have to start plants first in pots, transplanting seedlings when they are 2 inches high into the water-covered bed.
After the seedlings appear, in about 5 days, keep raising the water level until the plants are growing in water. In a small arrangement, it is not necessary to have moving water. However, a slow flow of water would be desirable.
One must learn by trial and error how to fertilize watercress. Start out by mixing 1 cup of garden fertilizer into 25 square feet of planting soil.
About 3 weeks after the seedlings appear, the plants are ready to harvest. Following cutting, they continue to grow and even appear to become thicker in the bed. Cuttings (12 inches long) from the old beds may be used to start new beds. To harvest, cut the tops of the plants about 6 inches below the tips. Gather them into bunches as they are cut. Trim the butt ends so the bunches are about 4 inches long. Thoroughly wash with clean water and place them into plastic bags to keep in the refrigerator crisper until used. Periodic sprinkling helps keep them fresh for about a week.
Watercress is a good source of vitamins A and C, along with niacin, ascorbic acid, thiamine, riboflavin, and iron. Although seldom used alone, watercress adds a zesty flavor to many other foods.