Question of the Week
Answer: Historically, the horticultural literature and government production bulletins on watercress were geared to field production in flooded beds. However, hydroponic production—indoors or outdoors—has emerged as a modern production method. The following material is divided into two parts: 1) standard outdoor production methods and resources, and 2) greenhouse and hydroponic methods and resources. Please note that cultural and post-harvest practices regarding watercress will be similar for outdoor and greenhouse production systems.
Outdoor Watercress Production
Watercress, Nasturtium officinale (synonym Rorippa nasturtium-aquaticum), is an aquatic, succulent, leafy plant in the mustard family (Cruciferae). It is a perennial plant but can be grown as an annual. Watercress grows wild in clear streams flowing through limestone formations in many parts of the southern and eastern U.S. The plant thrives in full sunlight and cool water.
Fresh leaves of watercress are used as salad greens and as a garnish. The leaves can be steamed and eaten as a vegetable. Watercress is nutritious, being high in minerals, protein, and vitamins (1).
Production of Watercress
Watercress production methods were developed by market gardeners outside London, England, in the 1800s. A site with a stream flowing across it is the basic requirement for getting into production. Ditches are dug adjacent to the stream, either perpendicular or parallel to the flow of water. The ditches are oriented north and south, if possible, and connected in a "zig-zag" fashion on a gradual slope to allow for water flow. More elaborate systems include side-by-side beds with wooden or concrete dikes and walkways.
Before watercress is established, the soil in the bottom of the trenches should be prepared much the same as a regular vegetable garden by adding several inches of compost and then tilling it in and raking it smooth. The bottom of the ditches is then filled with a half-inch of gravel to provide an anchor for the plant roots. Some growers in the northeastern U.S. use oyster shells for this purpose (2).
Commercial plantings of watercress are either direct-seeded or established in seedbeds and then transplanted (3). The soil should be slightly moist, with no water flowing at the time of planting. Seeding rates vary, but an average is around 1 lb. per 6,300 sq. ft. As the seedlings develop, water is let into the bed, but not enough to cover them. Seedlings 2 to 3 inches tall are big enough to transplant. Cuttings from wild patches of watercress can be used to establish beds as well. Seedlings and cuttings are usually transplanted to about 6 inches apart each way. Beds planted with seedlings started in the spring or from early summer cuttings produce a crop by late summer or autumn.
The primary watercress harvest is between March and October when the leafy crop grows above the water. The tops of the plants are cut by the handful about 6 inches below the tips and then gathered into bunches. Under favorable growing conditions, regrowth of the tops allows harvest about a month apart. In the winter watercress grows under water. Watercress can be pulled for harvest with the roots intact during this period, thinning the stand in the process. The roots are cut off before marketing the bunches.
In the article "Nature's Hydroponic Harvest" from The New Farm, listed below, Ohio farmer Dave McCoy describes his system of extending the harvest season by using a plastic mini A-frame greenhouse that sets directly over the spring.
Watercress can also be propagated and grown on a small scale in moist soils, beds, or pots. For home consumption, Taylor's Guide to Vegetables and Herbs (4) suggests growing watercress directly in 5- to 7-gallon containers in moist, neutral pH soil of moderate to high fertility. Johnny's Selected Seed Catalog (5) gave similar suggestions.
Storage and Shelflife
Storage and shelf-life of watercress factor into the marketing and handling of this highly perishable salad green. According to the USDA:
The high perishability of watercress makes prompt handling and refrigeration imperative. The leaves of watercress wilt and become yellow and slimy when improperly handled. Watercress should be precooled promptly after harvest, either by hydrocooling or vacuum cooling, and stored at 32° F. with high humidity (95 to 100 percent). It is bunched and usually packed in alternative layers with flake ice. Watercress stored at 32° F. in waxed cartons with top ice holds up well for 2 to 3 weeks. A similar storage life is possible by using perforated polyethylene crate liners and package icing to minimize wilting. Naked bunches of watercress are highly perishable, even at 32° F., and may keep only 3 or 4 days. In watercress, a 15-percent weight loss will cause only a trace of wilting, and a 40-percent weight loss will cause moderate wilting (6).
In research conducted by the United States Department of Agriculture, watercress held up well at 32° F. and 95% relative humidity for up to 4 weeks in perforated polyethylene bags, but only 4 days in naked bunches. At 68° F. and 60%relative humidity watercress held up for only 2 days in polyethylene bags and 1 day in naked bunches. Using container storage and top ice, watercress held up well for 2 to 3 weeks (7).
Two major diseases affect watercress. Crook root is a waterborne fungus (Spongospora subterranea f. nasturtii) that causes swollen and curved roots, stunting, and breakage of the anchor roots. The addition of zinc to the water reportedly controls the problem. Turnip mosaic virus is spread by several types of aphids, and can be controlled through seed propagation and insect control.
Many areas where watercress can be grown fall under the federal definition of a "wetland" and are subject to stringent restrictions. It may be necessary to apply for a wetlands permit from the Army Corps of Engineers. A farmer who modifies a wetland without a permit could be liable for all restoration costs.
While farming practices in wetlands are not regulated per se, dredging and filling operations are, so essentially any earth moving requires a permit. There may be state and/or local regulations governing activities in wetlands, in addition to federal regulations. Even wetlands previously converted to agriculture may be subject to regulation if for any reason they have reverted to functional wetland characteristics. The Natural Resources Conservation Service can assist farmers with soil-moving recommendations and information.
Watercress, a 53-page British growing guide by C.P. Stevens (8), is a production guide on this crop. It was published in 1983 by Grower Books in London. A common way to find out-of-print books is to borrow a copy through Inter-Library Loan.
Commercial Growing of Watercress, a USDA Farmers' Bulletin published in 1968, describes the climate, water supply, location and construction of beds, establishment, bed management practices, yields, and pest problems involved in watercress production.
Another resource is a bibliography on watercress compiled by the Aquacultural Information Center at the National Agricultural Library. If you have a need for any of the articles listed in this bibliography, check with Inter-Library Loan.
Greenhouse and Hydroponic Watercress Production
Watercress has traditionally been raised in outdoor beds with running water, in regions where spring water is abundant. Little has been published on greenhouse and hydroponic production systems for watercress, but modern production systems routinely employ these methods.
One hydroponic method that seems especially well suited is float bed hydroponics. The fact sheet below from the University of Kentucky provides an introduction to float bed hydroponics of selected edible greens. In the photo, please note the small plastic cups that hold a rooting substrate, which are then placed in styrofoam boards.
Production and Yield of Selected Edible Greens in Hydroponic Ponds
(Float Beds) in a Greenhouse
Robert Anderson, University of Kentucky
Please note the float bed method is widely used to raise tobacco transplants. But, the principles and practices of float bed technology can be equally applied to hydroponic herbs and vegetables. The best places to find resources on float bed production methods are agricultural colleges in Georgia, North Carolina, Tennessee, and Kentucky.
HortTechnology published a review article on watercress in 2001, focusing on the phytochemical properties in watercress that give health benefits. Watercress contains antioxidants, vitamins, and minerals, as well as high concentrations of a chemopreventive specific to tobacco carcinogens. In the notes on culture, it suggests that watercress can be grown in standard hydroponic solutions in beds with running water.
Palaniswamy, Usha R., and Richard J. McAvoy. 2001. Watercress: A salad crop with chemopreventive potential. HortTechnology. Vol. 11, No. 4. (October-December) p. 622–626.
The Growing Edge magazine published an article on watercress in 2003, “What would you grow in water?...watercress.” It features a grower in New Zealand, Glenn Woolsey, who perfected a hydroponic system for watercress production. The production system has worked so well that Woolsey has franchised an additional 24 farms for the production of watercress, which they sell in large volumes to a burdgeoning specialty greens market.
Some details are provided in The Growing Edge article, but it is obviously incomplete. I suppose a grower could pay Woolsey a consulting fee to get specifications and expert advice, or discuss the purchase and establishment of a franchise. Woolsey uses framed beds with a waterproof liner. The article provides essential clues, such as the use of capillary mats, electrical conductivity of the solution, and so forth.
Smith, Rob. 2003. What would you grow in water?... watercress. The Growing Edge. Vol. 14, No. 3. (January-February) p. 81–87.
Acta Horticulturae is the science journal of International Society for Horticultural Science. It published a research article on greenhouse watercress production. Seeds were directly sown into substrates in pots. The substrates that performed well included various types of poorly decomposed peats and a mixture of clay pebbles and peat. The pots sat in basins of slow flowing water, with topdress fertilizers supplying fertility.
Habegger, Ruth, M. Kohl, and D. Fritz. 1989. A cultivation method for Nasturtium officinale (watercress) grown in greenhouse. Acta Horticulturae. Vol. 242. p. 291–295.
Acta Horticulturae has a Web site that can be searched for citations to articles. Two abstracts on watercress production in greenhouses are provided below.
Title : A cultivation method for Nasturtium officinale (watercress) grown in greenhouse.
Call Number : A:PS
Author : Habegger, R.; Kohl, M.; Fritz, D.;
Source : ACTA HORTICULTURAE, no.242:291-295, 1989.
Language : En, Abst. in En,
Keywords : NASTURTIUM OFFICINALE/ WATERCRESS/ INDIGENOUS
VEGETABLES/ GREENHOUSES/ CULTIVATION/ METHODS/ SOWING/
LIQUID FERTILIZERS/ STEMS/
Abstract : Pot experiments were carried out to compare (1) the suitability of different substrates, and (2) crop yields achieved by direct sowing into different sized pots (7, 8, 9 or 10 cm diameter). Since watercress in its natural habitat grows in slowly flowing water, one experiment was set up in a basin with water dammed to a depth of 3 cm flowing through the basin. During cultivation, a liquid fertilizer was applied as required. In another experiment, the pots were placed in
a flowing fertilizer solution dammed to a depth of 2 cm. The harvested crop was assessed for FW, plant length and degree of branching. The highest FW was recorded in plants grown in a substrate mixture of TKS 1 (poorly decomposed peat) + Humosoil (poorly + well decomposed peat); plants in this substrate were well branched and compact. The FW of direct-sown plants increased with pot size, but plants grown in large pots produced thicker stems and had higher nitrate levels than plants grown in smaller pots, and their quality was therefore poorer.
ISHS Acta Horticulturae 614: VI International Symposium on Protected
Cultivation in Mild Winter Climate: Product and Process Innovation
Title: Yield and Quality of Lettuce Grown in Floating System Using Different
Sowing Density and Plant Spatial Arrangements
Authors: M. Gonnella, F. Serio, G. Conversa, P. Santamaria
Keywords: leafy vegetables, ready-to-use products, nitrate, hydroponic
Baby leaf vegetables (rocket, lamb’s lettuce, headless lettuce, endive, escarole, water cress) are mostly requested for mixed salads. Small-size leafy vegetables can be profitably cultivated in a floating system to obtain fresh market products or ready-to-use salads that are arousing more and more interest in consumers. Among hydroponic methods, the floating system is the easiest and cheapest way to produce baby leaf vegetables when soil cultivation is not feasible any more.
When re-circulation of nutrient solution (NS) is used, this system shows high water and fertiliser efficiency and low environmental impact. In the present study two cultivars of lettuce (Lactuca sativa L. var. longifolia) were used: 'Ronda' and 'Amadeus'. The growing cycle was carried out in the greenhouse in March-April 2000.
The growing set-up consisted of benches containing the NS and the floating boards. Two plant densities were adopted: 316 and 620 plant/m2. The latter was obtained using two different plant spatial arrangements. After 40 days of growth, fresh leaf yield was on average near to 6 kg/m2. Leaf dry matter content was on average 5 g/100 g of fresh weight (f.w.) without any differences between treatments. Contents of inorganic anions and cations were determined both in leaves and roots. Nitrate (NO3) content was generally lower than 2,000 mg/kg of f.w. and was not influenced by the treatments. Water consumption was near to 80 L/m2 regardless of plant density, while WUE resulted on average 3.5 g of leaf dry matter produced per litre of water consumed.
1) Simon, James E., Alena F. Chadwick, and Lyle E. Craker. 1984. Herbs: An Indexed Bibliography, 1971-1980. Archon Books, Hamden, CT. 770 p.
2) Pierce, Lincoln C. 1987. Vegetables: Production, Characteristics, and Marketing. John Wiley and Sons, New York, NY. p. 249.
3) Anon. 1987. Growing watercress commercially. The New Farm. July-August. p. 39.
4) DeWolf, Gordon P., Jr. (ed.) 1987. Taylor's Guide to Vegetables and Herbs. Houghton Mifflin Company, Boston, MA. p. 328-329.
5) Johnny's Selected Seeds Catalog. 1996. Albion, ME. p. 32.
6) Hardenburg, Robert E., Alley E. Watada, and Chien Yi Wang. 1986. The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Crops. USDA Agriculture Handbook No. 66. p. 72.
7) Hruschka, Howard W., and Chien Yi Wang. 1979. Storage and Shelf Life of Packaged Watercress, Parsley, and Mint. USDA/SEA Marketing Research Report No. 1102. 19 p.
8) Stevens, C.P. 1983. Watercress. ADAS/MAFF Reference Book 136. Grower Books, London, England. 53 p.
Resources on Standard Outdoor Production of Watercress:
McCoy, Dave. 1987. Nature's hydroponic harvest. The New Farm. July-August. p. 38-40.
Resh, Dr. Howard M. 1993. Outdoor hydroponic watercress production. p. 25-32. In: Proceedings of the 14th Annual Conference on Hydroponics. Growers Press, Inc., Princeton, B.C., Canada.
Shear, G.M. 1968. Commercial Growing of Watercress. USDA Farmer's Bulletin No. 2233. 12 p.
Young, Ann T., and Michelle E. Foster. 1990. Watercress. AIC Series No. 3. National Agricultural Library, Aquacultural Information Center, Beltsville, MD. 12 p.
Resources on Greenhouse and Hydroponic Production of Watercress:
Habegger, Ruth, M. Kohl, and D. Fritz. 1989. A cultivation method for Nasturtium officinale (watercress) grown in greenhouse. Acta Horticulturae. Vol. 242. p. 291–295. (Abstract)
Palaniswamy, Usha R. and Richard J. McAvoy. 2001. Watercress: A salad crop with chemopreventive potential. HortTechnology. Vol. 11, No. 4. (October-December) p. 622–626.
Production and Yield of Selected Edible Greens in Hydroponic Ponds (Float Beds) in a Greenhouse
Robert Anderson, University of Kentucky
Smith, Rob. 2003. What would you grow in water?... watercress. The Growing Edge. Vol. 14, No. 3. (January-February) p. 81–87.
Anon. 1967. Watercress Growing. Bulletin No. 136. Ministries of Agriculture, Fisheries, and Food (Great Britain), H.M.S.O., London, England. 35 p.
Anon. 1995. Decatur Michigan’s Flint Mengel builds upon watercress success. The Great Lakes Vegetable Growers News. May. p. 1, 44.
Belair, Lina. 1992. Watercress, An aquatic treasure. Minnesota Horticulturist. August–September. p. 20–21.
Hoare, A.H. 1924. Watercress and its cultivation. Journal of Ministry of Agriculture (Great Britain). Vol. 30. p. 1147-56.
McHugh, J., S. Fukuda, and K. Takeda. 1981. Watercress Production in Hawaii. Resource Publication 012-11/81. University of Hawaii.
Shear, G.M. 1949. Watercress growing. Virginia Agricultural Experiment Station. Virginia Polytechnic Institute. Blacksburg, VA. 15 p.
Spencer, D.M., and H.H. Glasscock. 1953. Crook root of watercress. Plant Pathology. Vol. 2. p. 19-21.
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