Last revised February 15, 2010
Spinach. Photo credit: Alex Stone, Oregon State University
The use of proper varieties is very important. Slow-growing, slow-bolting (slow seed-stalk development as day length increases) varieties are used for late spring and summer harvest, while fast-growing (these tend to be fast bolting), vigorous varieties should be used for fall, winter, and early spring harvest. Although long days and increasing temperature predispose spinach to bolting, bolting is increased by exposure of young plants to low (40-60 F) temperatures.
Disease resistance in spinach varieties is developed for the season to which the variety is adapted. With proper varieties, spinach production for the fresh market is possible almost year-round in western Oregon.
Traditionally, prickly-seeded varieties were known as fall harvest, and winter types, while round-seeded varieties were referred to as summer spinach. However, new varieties of round-seeded spinach make these designations less accurate.
Flat, semisavoy, and savoy leaf varieties are used for different markets. The flat and some of the semisavoy varieties are used for processing. All three types are used for fresh market with semisavoy and savoy types predominating.
Spinach varieties may also be classified as prostrate, semi-erect, and upright. When the savoy types are used for processing, plant growth regulators may sometimes be applied before harvest to cause a more upright leaf growth and reduce the risk of soil contamination. This is important due to the difficulty in removing soil from savoy leaves during washing and processing.
SPINACH VARIETIES (approximately 40-50 days).
See the Vegetable Variety Selection Resources page to find varieties that have been shown to perform well in the Pacific NW.
Spinach is direct seeded from March through September as weather permits. Planting dates for certain varieties are chosen so as to grow the most vigorous variety possible and yet avoid the risk of bolting. Bolting risk increases as daylength, temperature, and plant density increases and as soil moisture or plant nutrients decrease. Suggested varieties are:
|Planting Dates||Leaf Type and Variety|
|Early (winter or before May 1)||Baker, Polka, Symphony, Wolter||Avon, Baker, Melody, Skookum, Tyee, Indian Summer||Savoy Supreme|
Exceptional bolting tolerance: Bejo 1369, Splendor
Asian leaf type for trial: Imperial Sun.
Resistance to Downy Mildew strains 1,2,3 and 4: Bolero, Bossanova (both flat leaf)
|Mid-season (May 1 to July 31)||Baker, Olympia, Polka, Symphony||Melody, Skookum Tyee, Indian Summer, Mazurka||Bloomsdale L.S.|
Exceptional bolting tolerance: Bejo 1369, Splendor
Beet Western Yellows tolerance for trial: Ambassador, Rainier, Rhythm 9, and Hybrid#7
|Late (August 1 to mid-September)||Baker, Olympia, Polka, Wolter St. Helens, Hybrid 424, Estivato||Avon, Chinook II Hyb.#7, No.7R, Skookum||Iron Prince, Vienna|
|Overwinter (mid to late September)||Baker, Cascade, St. Helens, Hybrid 424, Wolter||Chinook II, No. 7||Iron Prince|
Other types of leaf vegetables:
New Zealand spinach (Tetragonia tetragonioides) is a tender annual with fleshy stems and leaves, resembling spinach. It has very limited commercial demand, but because of its adaptability to hot summer temperatures and drought, it is popular among some home gardeners.
Spinach beet and Swiss chard (Beta vulgaris Cicla group), a form of common table beet or leaf beet, grown for their succulent leaves which can be harvested over an extended period. Swiss chard has large, well developed petioles that may be red, white or green. These are grown for limited markets, and primarily in home gardens. Sugar beet leaves may also be used as a substitute for spinach, and are considered superior to table beet leaves. See separate file Beets and Chard.
Malabar spinach is in a different family altogether. The genus is Basella, and three species are common: B. rubra, B. alba, and B. cordifolia, which are red stem, green stem, and heart-shaped leaf forms, respectively. This is a warm-season crop which produces aggressive vines that may reach 10-15 feet in length. The succulent leaves and tender shoots are marketed at specialty markets and are used the same as spinach.
Muck soils provide needed organic matter and high, uniform, moisture content. Sandy loams may be used. A pH of 6.2 to 6.9 is optimum with a pH. between 6.5 and 7.0 being ideal for good growth. Spinach grows very poorly at pH below 6.0.
SEED AND SEED TREATMENT
Summer spinach variety seed numbers approximately 2,800 per ounce, while New Zealand spinach seed numbers about 350 per ounce. Use only seed that has been fungicide-treated. Spinach is susceptible to damping off.
Recent research indicates that a temperature of 50-63 F is ideal for optimal growth.
Use a precision seeder to plant about 10 seeds per lineal foot of row. This will provide about 6-8 plants per foot, the desired stand. Space rows in sets 10-12 inches apart or singly 18-36 inches apart (about 125,000 to 200,000 plants per acre). This method will require 3-4 lb seed per acre if a precision seeder is used. Without a precision seeder, approximately 10-15 lb of seed (480,000-720,000 seeds) per acre are often used. Generally a lower seeding rate is used when spinach is planted for processing, and a higher rate when spinach is to be bunched or bagged. Seeding rates should be reduced when spinach is to be grown during high temperatures.
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. As a general guideline broadcast and disc in the following:
|Muck Soils||Mineral Soils|
|Nitrogen (N)||30- 50 lb/acre||60-100 lb/acre|
|Phosphate (P205)||100-150 lb/acre||100-150 lb/acre|
|Potash (K20)||0-150 lb/acre||0-150 lb/acre|
Micronutrients should be applied only on the basis of soil test.
Spinach is a quick-growing, shallow-rooted crop that is not tolerant of water stress. Maintain adequate moisture by frequent irrigation when necessary but avoid irrigation practices that splash soil onto the leaves or damage them.
See also the OSU Irrigation Guide for Leafy Greens.
Gibberellic acid (GA) is labelled for use on fall-planted and over-wintered spinach (except in California) to facilitate harvest, to increase yield, and to improve crop quality. The label calls for a single spray of 6-8 g ai/acre in 10-50 gal/acre, 10-18 days before each anticipated harvest. Applications should be made when the temperature is at least 40 oF and when dew is present on the leaves. Check the label for other suggestions/restrictions. Bolting may be promoted if temperatures exceed 75 oF within several days of application. Caution: the use of GA on spinach is suggested for trial only in the Pacific Northwest. We lack experience with this procedure under our climatic conditions.
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.
Spinach for processing yields are approximately 8 to 10 tons per acre. Average fresh market yields nationally in 1993 ranged from 160 25-lb bushels per acre in Virginia to 840 bu/acre in California. The national average yield for six reporting states was 524 bu/acre. Oregon yields are commonly 700-900 22-lb cases/acre.
For processing - harvest before plants are too large or begin to bolt (usually when 16" to 17" tall). Sometimes a second cut is made for a chopped pack after suitable regrowth has developed.
At harvest, the first cut is made 6-7 inches above the ground in order to eliminate as much stem and petiole as possible for the whole leaf pack. This also is done to avoid as many of the yellow or old leaves as possible. At the second cutting, small disks are used to cut away these yellow or old leaves and to remove some soil away from the crown to facilitate harvest. Depending on temperature, and plant density, 3-4 weeks are needed between the first and second cutting to obtain adequate regrowth.
A number of mechanical harvesters are available for processing spinach.
For fresh market - plants should be dry and slightly wilted to prevent petiole breakage. When harvesting by hand, cut above the crown or soil line and bunch. Care should be taken to exclude leaves that are dirty with soil or are yellow. Bunched spinach must be handled extra carefully to reduce breakage of plants or bunches during bunching, washing and packaging.
Specialty leaf lettuces and spinach for bag mixes have usually been hand harvested, but mechanical harvesters for this purpose are now available.
STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)
Hold spinach at 32 F and 95 to 100% relative humidity. Spinach is very perishable; hence, it can be stored for only 10 to 14 days. The temperature should be as close to 32 F as possible because spinach deteriorates rapidly at higher temperatures. Crushed ice should be placed in each package for rapid cooling and for removing the heat of respiration. Top ice is also beneficial. Hydro-cooling and vacuum cooling are other satisfactory cooling methods for spinach.
Most spinach for fresh market is prepackaged in perforated plastic bags to reduce moisture loss and physical injury. Controlled atmospheres with 10 to 40 percent carbon dioxide and 10% oxygen have been found to be beneficial in retarding yellowing and maintaining quality.
Spinach is commonly packaged in 20 to 22-lb cartons packed 2 dozen each; or 7.5 to 8-lb cartons of 12 film bags, each 10 oz; or 20 to 25-lb bushel crates.