Last revised February 12, 2010
Summer squash is defined as fruit of the Cucurbitaceae family that are consumed when immature, 100% of the fruit of which is edible either cooked or raw, once picked is not suited for long-term storage, has a soft rind which is easily penetrated, and the seeds of which would not germinate at harvest maturity: e.g. Cucurbita pepo (i.e. crookneck squash, straightneck squash, scallop squash, zucchini, vegetable marrow).
Other genera in the Cucurbitaceae family whose fruit may be consumed when immature include Lagenaria spp. (i.e. hyotan, cucuzza); Luffa spp. (i.e. hechima, Chinese okra); Memordica spp. (i.e. bitter melon, balsam pear, balsam apple, Chinese cucumber); and other varieties and/or hybrids of these. Production practices for all these species are similar to those described below for summer squash.
Summer Squash. Photo credit: Bill Mansour, Oregon State University
See the Vegetable Variety Selection Resources page to find varieties that have been shown to perform well in the Pacific NW.
Vegetable Sponge, Dishcloth gourd, Sponge gourd (Luffa sp.). These may be used for cooking when immature (approximately 75 days), or allowed to mature for the fibrous spongy tissue (approximately 115 days): Angular types (Luffa acutangula): San-C, Ping-Ann. Cylindrical types (Luffa aegyptica): Cylinder, Seven Star, Seven Beauty. These produce higher quality sponge fiber.
Balsam pear, Bitter melon (Momordica charantia, approximately 75 days): Green: Known-You Green. White: Moon Shine, Known-You No.2
SEED AND SEED TREATMENT
Zucchini and most summer squash seed number approximately 200-300 per ounce. Use fungicide-treated seed. Summer squash seedlings are susceptible to damping off and decay when soils are cool and wet.
SOIL TYPE AND TEMPERATURE
Zucchini grows best on fertile, well-drained soil supplied with organic matter. The ideal pH for zucchini growth is between 6.0 to 7.5, but it will grow on soils with a pH of up to 8.0. Consult a soil test for fertilizer and liming recommendations.
The minimum soil temperature required for germination of zucchini is 60 F, with the optimum range between 70 and 95 F.
Zucchini are usually direct-seeded when all danger of frost has passed. In western Oregon planting begins in early May and extends to mid-July. Stagger plantings 10 to 14 days apart to maintain a continuous supply of high quality product.
Use 36 to 40-inch spacing between rows with plants 18-36 inches apart within the row.
For the most current advice, see Nutrient Management for Sustainable Vegetable Cropping Systems in Western Oregon, available as a free download from the OSU Extension Catalog
A soil test is the most accurate guide to fertilizer requirements. The following recommendations are general guidelines:
The optimum pH range is 5.8-7.0.
Apply 10 tons/acre of manure in the spring when available.
Western Oregon - At time of seeding, band 2 inches to the side of the seed and 3 inches deep the following:
Nitrogen: 50-70 (N) lb/acre. (Sidedress with an additional 30-60 lb N per acre when plants begin to flower).
Phosphate: 115-125 (P2O5) lb/acre.
Potash: 50-100 lb K2O/acre (broadcast and disked-in prior to seeding).
Eastern Oregon - At time of seeding, band the following:
Nitrogen: 40-60 (N) lb/acre
Phosphate: 115-125 (P2O5) lb/acre
Potash: 50-100 lb K2O/acre (broadcast and disked in prior to seeding).
Sidedress with 25-50 lb N/acre, or where mulching and trickle irrigation are practiced, N can be fed through the trickle irrigation system at 15-25 lb/acre when the vines begin to spread. To prevent clogging or plugging from occurring use soluble forms of nitrogen (urea or ammonium nitrate) and chlorinate the system once a month with a l0-50 ppm chlorine solution. Chlorinate more frequently if the flow rate decreases.
Summer squash roots to a depth of 3-4 feet. Maintain soil moisture above 60% of the soil water holding capacity. In western Oregon, 12-15 inches of irrigation may be necessary. Approximate summer irrigation needs for the Hermiston area have been found to be 3.5 inches in May, 5.0 in June, 7.5 in July, and 7.0 in August. It is important to regulate irrigation properly to avoid excessive moisture or water stress. Research has shown that the use of drip irrigation under black plastic mulch is superior to sprinkler irrigation with black plastic mulch. Yields usually increase dramatically.
See also the OSU Irrigation Guide for this crop.
FLOWERING AND POLLINATION
Zucchini and summer squash plants bear separate male and female flowers on the same plant (monoecious). Only the female flowers set fruit. Bees transfer pollen from male flowers to female flowers, making fruit set possible. It is recommended that one honey bee hive should be introduced for every 1 to 2 acres during the blooming period since native bee populations may not be adequate, or may not coincide properly with the blooming period.
Questions come up about cucumbers, melons, gourds, and summer and winter squash, crossing and affecting the eating quality of one vine crop or another. This is NOT a problem. Intercrossing is only a problem when seed is saved for replanting, in which case squashes of the SAME species need to be isolated for crop purity. Cucurbits of different species do not intercross sufficiently to create problems for seed producers.
GROUND MULCHES AND ROW COVERS
Black plastic ground mulch is sometimes used in the production of summer squash to enhance yield and earliness. It controls weeds, may increase soil temperature, conserves moisture, and protects fruit from ground rots. For black plastic mulch to increase soil temperature, it is imperative that the soil surface be smooth and that the plastic be in close contact with the soil. This can only be achieved by laying the plastic with a machine designed and properly adjusted for this task. Clear plastic mulch is very effective at transferring heat to the soil, but does not control weeds.
A new generation of plastic mulch films allows for good weed control together with soil warming that is intermediate between black plastic and clear film. These films are called IRT (infrared-transmitting) or wavelength-selective films. They are more expensive than black or clear films, but appear to be cost-effective where soil warming is important.
Plastic, spunbonded, and non-woven materials have been developed as crop covers for use as windbreaks, for frost protection, and to enhance yield and earliness. They complement the use of plastic mulch and drip irrigation in many crops.
Non-woven or spunbonded polyester and perforated polyethylene row covers may be used for 4 to 8 weeks immediately after transplanting or seeding especially for summer squash (such as zucchini) where the added cost could be recovered through increased early season prices. Covers should be removed when plants begin to flower to allow proper pollination. Row covers increase heat unit accumulation by 2 to 3 times over ambient. Two to four degrees of frost protection may also be obtained at night. Soil temperatures and root growth are also increased under row covers as are early yields, and in many cases total yields.
A new insect exclusion cover (Agryl P-10), is very light weight, offering season-long insect vector exclusion without affecting canopy temperature very much. It is recommended for trial in situations were conventional virus vector control procedures are inadequate, and market economics justify. It must be frequently manipulated; removed to allow bee pollination, and re-applied as necessary to exclude aphid virus vectors.
HARVESTING, HANDLING, AND STORAGE
The University of California-Davis has a file on Minimal Processing of Fresh Vegetables that discusses film wrapping and other topics.
In the Willamette Valley, summer squash and zucchini is harvested for processing from July 7 to September 20. The prime harvest period is from July 25 to August 25. Fresh-market plantings may be harvested up to two weeks earlier than this when transplanted on mulch and rowcovers are used. Fields are normally harvested every 2 to 3 days in warm weather. Cut fruit from the vine, leaving a piece of stem with the fruit.
Yields of zucchini for processing of approximately 20-25 tons/acre can be obtained form multiple harvests with zucchini planted at 24x36-inch spacing. Zucchini and summer squash can be harvested anytime fruits reach the desired size but before they forms hard seeds or rinds. For processing, zucchini is graded by diameter: Grade #1: 1"-2"; #2: 2"-2.25"; #3: 2.25"-2.50"; anything over 2.5" is rejected.
Fresh market yields are approximately 150 to 300 cwt/acre depending on the number of pickings. When using appropriate plasticulture techniques, yields of 360 cwt/acre have been reported. Crook-neck, straight-neck and zucchini should be 1.25 to 2 inches in diameter and zucchini and straight-neck squash 7 to 8 inches long. Scallops should be 3 to 4 inches in diameter
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Processing squash is not normally stored. For fresh market, store zucchini and summer squashes at 40 to 50 F and 95% relative humidity. Summer squashes, such as Yellow Crookneck, Yellow Straightneck, White Scallop, Zucchini, and other soft-skin types are harvested at the immature stage for best quality. They are quite perishable, as the skin is tender and easily wounded in handling. Small fruits are more desirable than large ones because they have a more tender flesh and a slightly sweet flavor.
Normally they should not be stored except long enough to accommodate normal marketing delays such as holidays and weekends. They can be held 1 or 2 days below 40 F with no discernible damage, but such exposure should be avoided as summer squash is chilling sensitive. Holding summer squash longer than 4 days at 32 F will cause chilling damage and more rapid deterioration.
The recommended temperature range is 41 to 50 F with 95% relative humidity. The storage life of summer squash is only 1 to 2 weeks. If storage of yellow squash extends beyond a week and distribution is involved after removal, storage at temperatures of 45 to 50 F is best. The storage period at 45 to 50 should be limited to 2 weeks or less. Recent research has shown that 41 F is best for Zucchini squash stored up to 2 weeks. Storage in low-oxygen atmospheres was of little or no value for Zucchini squash held at 41 F.
Zucchini and summer squash are usually packaged in 21-pound (5/9 bushel) crates and cartons; 24 to 28-pound cartons and L.A. lugs; 18 to 22- pound three-quarters lugs; 41-pound (1-1/9 bushel) crates; or 21-pound (l/2 bushel) baskets and cartons.