Spinach

Introduction

Spinach is a hardy cool weather crop, grown for use as a cooked green vegetable or for salad greens. Temperature for optimum production and high quality is 55°F to 60°F with day length of approximately 12 hours. Under the hot temperatures and long days of summer, spinach will bolt (develop a seed stalk and flower), which reduces quality. The tendency to bolt varies with the cultivar, some being more resistant than others. Growers who want greens in summer should consider beet greens and/or Swiss chard as substitutes, since they produce well under high temperature and long day conditions.

Types and Varieties

There are two main types of spinach: smooth leaf and savoy (crinkled leaf). Both grow equally well and are marketed similarly, but the savoy type, because of its crinkled leaf, is more difficult to clean. Asian leaf types are relatively smooth with pointed leaves. 

Spinach Varieties Type Season Resistances
Ashley savoy SF  
Corvair smooth W DM1-11, 13
Flamingo asian SFW DM1-11, 12, 13
Gazelle smooth FW DM1-13
Giant Winter OP savoy W  
Pigeon smooth W DM1-13
Renegade smooth SFW DM1-7, 11, 13, 15, CMV
Red Kitten smooth W DM1-11
Samish savoy F DM1-4
Space smooth FW DM1-3, 5, 6, 8, 11, 12, CLS
Tyee savoy SFW DM1, 3, 5, 8, 9, 11, 12
Unipak 151 savoy S DM1-4, CMV
Whale smooth SF DM1-7
Winter Bloomsdale OP savoy W CMV

OP = open-pollinated, Seasons: S = spring, F = fall, W = winter. 

Resistant or tolerant to: DM: Downy Mildew (races indicated), CMV: Cucumber Mosaic Virus, CLS: Cladosporium leaf spot

 

Soil Fertility

Apply lime according to soil test results to maintain soil pH at 6.5 to 6.8. Soils with low pH will result in slow growth and chlorotic leaves.

Because of sensitivity to magnesium deficiency, older spinach leaves may tend to show yellow color similar to a nitrogen deficiency. Low levels of magnesium in the soil can be corrected by using high magnesium lime (dolomitic) or by adding magnesium to the fertilizer. Do not automatically apply more nitrogen to try to develop the desired deep green color. Rather, make a topical application of 10 to 15 lb magnesium sulfate (Epsom salts) in 100 gal water. Spray to wet the foliage.

If magnesium was deficient, you will see a color change to dark green overnight. Spinach will accumulate excess nitrates if nitrogen is used in an attempt to induce green color. It is always best to check for magnesium problems before applying extra nitrogen if plants have chlorotic pale green color or yellow lower leaves.

Promote efficient nitrogen use by sidedressing nitrogen when crop need is apparent. Avoid putting fertilizer directly onto crop foliage.

Less nitrogen fertilizer will be needed if manure or legume sod was plowed down (see Table 1, Nitrogen Credits from Manure and Table 2, Nitrogen Credits from Previous Crops).

PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR SPINACH
SPINACH NITROGEN (N)* LBS PER ACRE PHOSPHORUS (P) LBS P2O5  PER ACRE    POTASSIUM (K) LBS K2O      PER ACRE
SOIL TEST RESULTS   VERY LOW LOW OPTIMUM ABOVE OPTIMUM VERY LOW LOW OPTIMUM ABOVE OPTIMUM
Broadcast and Incorporate 60-80 180 120 30-60 0-30 180 120 30-60 0
Sidedress 3-4 Weeks after Planting 30 0 0 0 0 0 0 0 0
TOTAL RECOMMENDED 90-110 180 120 30-60 0-30 180 120 30-60 0
*SEE PLANT NUTRIENTS FOR INFORMATION ON NUTRIENT MANAGEMENT AND APPLICATION.

Planting

Seed will germinate at soil temperatures of 32°F to 60°F. Soil temperatures above 700F will result in poor germination. Priming the seed may improve germination. Spinach seed is short-lived and susceptible to damping-off. For good stands start with new, fungicide treated seed each year.

Desired plant stand is 6 to 8 plants per foot of row and 12" between rows. This requires 8 to 10 lb of seed per acre (1/2 to 1 oz per 100 feet of row). After preparing a stale seedbed, seeds may also be broadcast for a denser planting to help control weeds. During dry conditions, irrigation may be necessary to germinate seeds. Seed 0.25" to 0.5" deep depending on soil moisture and temperature. Deeper planting is suggested in a warm dry soil. Growers should attempt to seed to a stand as thinning is generally not recommended. 

Field Culture

Main season (spring and fall). Spinach can be seeded in the spring as soon as the soil can be worked. Sandy soils are generally preferred because they drain early and warm a little quicker. Two main crops are generally grown, one in the spring, another in late summer, seeded about 6 weeks before the average first frost.

Winter. Winter production of spinach by New England growers is now quite popular. A floating row cover, high or low tunnel or combination can be used for protection. Survival of the early, over-wintered crop has been satisfactory following a mild winter with good snow cover. For overwintering spinach, particularly in northern areas, an early September seeding date is suggested. Germination can be poor in tunnels with warm soil temperatures (>70F). Plant growth slows with less than 10 hours of light per day. Aim to have 4-5 true leaves on plant before you reach this point. Most growers will transplant spinach for winter production to ensure a good stand.

Because of the importance of downy mildew in cool humid conditions, chose varieties with downy mildew resistance for winter culture.

There are three common physiological disorders that may occur on winter-grown spinach in high tunnels. Freezing damage can kill and brown leaf tissue. This can be minimized by using secondary row covers or low tunnels inside high tunnels. Oedema results when water pressure causes cells to burst, resulting in scab-like calluses on the leaves. It can be minimized by limiting irrigation and managing relative humidity as temperatures drop and growth slows. Under winter and spring conditions in high tunnels, spinach often forms natural leaf structures (glandular trichomes) on upper and lower leaf surfaces, which resemble tiny water droplets or insect eggs, but actually arise from the leaf surface on tiny stalks. These trichomes often cause concern, but are harmless.

Harvest

Spinach can be harvested from 37 to 45 days after seeding, but can take much longer to mature during late fall and winter months. Often, individual leaves are harvested, but the entire plant can be cut off just above ground level when there are 5 to 6 leaves. Higher yields result when plants have 10 to 12 leaves. Good yields for fresh market will range from 5 to 7 tons/A and 10 to 12 tons/A for processing. Market spinach is usually washed before marketing, and if cut early in the day and iced, can have a storage life of 10 to 14 days. The most common containers are bushel baskets, tubs or crates, each holding 18 to 25 lb.

Spinach is sometimes field packed loose into crates or cartons averaging 18 lb net. Whole plants are sometimes bunched, like carrots, when going directly to retail markets. Spinach is usually washed before being marketed. Spinach should be kept cool and shaded after harvest. In summer and fall, spinach harvested early in the day and cooled immediately will have a much better shelf life. Frozen leaves can be damaged during harvest. During winter production, harvest later in the day, after leaves have thawed. Storage life is 10 to 14 days. Package as bushel baskets or crates containing 20 to 25 lb, cartons or wire-bound crates with 2 dozen bunches each, or 12 film bags (10 oz per bag) in a master carton.