Luffa, Sponge Gourd, Chinese Okra
Luffa cylindrica and Luffa acutangula are members of the Cucurbitaceae (gourd) family and are related to cucumber, muskmelons, and squash.
The Luffa is not well known in the vegetable community and has very minor acreage in California, but the unique nature of the fruits, which are used both for food and industrial purposes, prompts interest in the plants. Chinese okra, Luffa acutangula, is a food crop that is grown for its immature fruit. Luffa cylindrica, sponge gourd, is grown principally for sponge production as the name implies. Both species reportedly originated in India.
Both species have vigorous climbing vines with yellow flowers. In most cultivars, male and female flowers are produced separately in the axils of the leaves. Some hermaphroditic cultivars (male and female organs in same flower) are known. Pollination is by insects, primarily various bee species. The flowering habit differs for the two species: flowers of sponge gourd open during the day, whereas the flowers of Chinese okra open in late afternoon and remain open during the night. In both species, flowers are only open and receptive to pollination for one day.
Luffa cylindrica is distinguished from L acutangula by its smooth, cylindrical fruit. Luffa acutangula fruit is also cylindrical but has a tapering neck and 10 prominent longitudinal ridges. Both fruits are generally 2 to 3 inches in diameter and 15 to 18 inches in length.
Other names. Skoo ah (Hmong); hechima (Japanese); sinqua (Cantonese Chinese); ta tsu kua (Mandarin Chinese); shui kwa, sing gwa, see kwa (Chinese); patola, patolang, cabatiti (Filipino); muop khia (Vietnamese); tooria, toorai, ghosala (Indian). It is also known as smooth gourd, dishrag gourd, or loofah.
Use. Luffa cylindrica , sponge gourd, is grown mainly for the tough fibrous netting that remains after the pulpy flesh is removed from the mature fruit. The fibrous netting makes excellent sponges that are valued for use in the bath or as dish and pot scrubbers. Other important uses of the spongy material are for marine steam engine filters, doormats, table mats, mattress, or shoulder pad stuffing, and for absorbing sound.
The spongy network is also present in mature fruits of the Luffa acutangula but the quality is inferior to the smooth gourd and, therefore it is rarely grown for its spongy characteristic. Immature fruits of this species are known as "Chinese okra" and may be eaten cooked or raw, like summer squash or cucumbers. Fruits are harvested when 4 to 6 inches in length while they are still tender and before the fibrous network develops.
Yield. Reports form Japan and India indicates that for sponge production a good yield is about 25,000 fruits per acre. On this basis, with a plant density of 4,400 plants per acre (24 inches in the row on 60 inch spacing), the number of fruit per plant should be limited to five or six.
Climatic requirements. Luffas are warm-season plants that prefer average monthly temperatures in the range of 18° to 24°C, with daytime highs of 30° to 35°C. The plants are sensitive to frost. Luffas perform well from spring planting anywhere in the southern United States. However reports indicate that successful planting have been grown as far north as Connecticut and even Maine, so it may be possible to produce crops of Luffa in northern as well as southern California.
Propagation and care. Soil and irrigation requirements are similar to those for summer squash, cucumbers, or muskmelons. A deep sandy loam would be ideal, but with proper management, successful crops can be grown on any good agricultural soil. Fertilizer requirements of these crops have not been studied, but programs which are commonly used for other cucurbits should be adequate, e.g., nitrogen at 150 lb/A, phosphorus at 50 lb/A, and potassium and other elements when soil analysis indicates need. Apply one-third of the nitrogen and all the phosphorus before planting, either broadcast and disked in, or in a band a few inches to the side and below the plant line. Animal manures can be applied and incorporated a few weeks prior to planting to supply part of the nutritional requirements. Irrigation practices should be managed to maintain good soil moisture in the top 18 inches of soil where the major root system is located. Drip irrigation can be used successfully on Luffa plantings and provides the most efficient use of water.
Planting can be established by direct seeding or transplanting. Grow transplants by a method that will avoid disturbances of the root system during planting. Plants should be set in the field at the 2 to 3-true leaf stage. When direct seeding, place the seed 1 inch deep - the objective is to have a final stand of plants placed about 18 to 24 inches apart in the row. The effect of spacing on fruit size and yield has not been studied, but the suggested spacing is as reported in countries where these crops are commonly grown. Single rows should be spaced 5 to 6 feet apart. A trellis about 6 feet in height is required to support the climbing vine. Stakes should be 3 to 4 feet apart with a network of vertical strings.
Flowering and fruit setting begins approximately 6 weeks following seeding under conditions of warm temperatures and good nutrition. Good bee activity in the planting is essential for good fruit set. When harvest of immature fruits (Chinese okra) is the objective, harvest should be frequent enough to remove all fruits as they attain marketable size in order to obtain maximum yield. Maturing ribs suppress the development of younger ones. Evidence suggest that for sponge production (sponge gourd) it is good practice to limit the number of fruits per plant so as to produce the fruits of optimum size, To accomplish this, some of the earliest setting fruit can be removed; later setting fruits may need to be thinned. The relationship between plant spacing, fruit size and number of fruit per plant is an important consideration in the economics of sponge fruit production. The evidence is not yet clear in Luffa, but in other cucurbits, optimum spacing have been found to maximize fruit yield of the most desirable size.
Pests. All cucurbits are susceptible to many of the same diseases and insect pests, such as nematodes, viruses, powdery mildew, leaf miners and spider mites.
A pesticide used on Luffa must be specifically labeled for use on that crop, or for cucurbits in general. An amendment to the federal pesticide regulations (June 29, 1983) groups several minor cucurbits, including Luffa, so that residue tolerances for pesticides labeled for use on cucumbers, muskmelons, and summer squash could be used on Luffa if the pesticide manufacturer chooses to obtain a group residue tolerance and include that on the label.
Harvest and postharvest practices. The basic method for preparing the sponge material is to immerse the dry, mature fruit in water for a few days to soften the skin and flesh so that it can be easily removed. Other processing methods include freezing or using boiling water. Once cleansed of seeds and flesh, the fibrous network is dried and, for some purposes, bleached in hydrogen peroxide. Various varieties are available that differ in diameter, length, and quality of fiber. Immature fruit of sponge gourd is rarely used for food in this country, but in India sweet varieties are grown for this purpose.
Immature Luffa fruits harvested for food purposes are likely to be susceptible to chilling injury, similar to cucumbers and summer squash, consequently refrigerated storage should not be below 50°F. Storage conditions have not been studied for Luffa fruits, but storage is probably relatively short. To maintain the best quality, it is suggested that fruit be marketed within a few days following harvest. Young fruits have tender skin, thus care should be taken during harvest and packaging. Fruits should be cut from the plant rather than pulled to avoid plant damage.
W. Atlee Burpee & Company, 300 Park Avenue, Warmister, PA 18974
Sunrise Enterprises, P. O. Box 10058, Elmwood, CT 06110-0058
Johnny's Selected Seeds, Foss Hill Road, Albion, Maine 04910
Tsang and Ma, P. O. Box 5644, Redwood City, CA 94063
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The author is Hunter Johnson, Jr., Vegetable Specialist Emeritus, Cooperative Extension, UC Riverside.