Introduction
Spinach (Spinacia oleracea) known as vilayati palak in Hindi, is a typical cool season or temperate leafy vegetable. As against beet leaf spinach, which is hermaphrodite, vilayati spinach is dioecious. In India, its cultivation is limited to home gardens of hilly regions and is used as a cooked vegetable.
Spinach is a rich source of calcium, magnesium, phosphorus, potassium, and zinc. Major vitamins of spinach include vitamin C, A, E, folic acid, niacin, and vitamin K. Spinach is also rich in carotenoids among which lutein, zeaxanthin, and beta carotene are the major ones. Glutamic acid, aspartic acid, and leucine are the major amino acids of spinach. Being high in zinc and folic acid content, spinach is an appropriate vegetable for pregnant women.
Table of Contents (toc)
Climate and soil
It thrives best during cool weather and withstands frost. It cannot do well in hot weather. Favorable temperature for best yields ranges from 16-21°C under short-day conditions. For normal growth, spinach requires a cool climate and is hence suited as a winter crop in plains. Warm-season and long days induce plants to flower.
The soil should not be too heavy and pH should be in the range of 6-8 (mildly acid to mildly alkaline). Acid soils. may require the addition of lime to bring them closer to neutrality. Spinach can be grown in well-drained, fertile soil, high in organic matter, and consistent moisture. It tolerates slightly alkaline soils but is sensitive to acid soils.
Varieties
Based on types of seeds (prickly seeded and smooth seeded) and leaf characteristics (smooth leaved and savoy leaved), cultivars are divided into different groups. A good variety should have dark green leaves without a stem. Crisp, succulent, and savoy leaves are preferred for the fresh market while flat and smooth leaves for processing. Savoy (wrinkled), semi-savoy, and smooth-leaved varieties exist. Virginia Savoy and Early Smooth Leaf are improved exotic varieties. Banerjee Giant, Banarasi (Katvi palak), Khara Lucknow, and Khara palak are popular desi-type varieties adapted to Indian conditions.
Early Smooth Leaf: This is a smooth seeded cultivar producing small light green leaves with a pointed tip.
Virginia Savoy: It is a prickly cultivar having blistered large green leaves with a round tip. Plants are upright and vigorous in growth.
Propagation
Spinach is propagated by seeds. On average, 35 to 40 kg seed/ha is enough. If the proportions of male seeds are more in the seed lot, a higher seed rate is required. Spinach seeds can geminate from 2-30°C. However, 7-24°C is optimum. Seeds will not germinate well in warm weather. Although spinach will grow in temperatures ranging from 5-24°C, growth is most rapid at 15-18°C.
Cultivation
Planting
Pre-sowing land preparation involves thorough ploughing 3-4 times and planking. Beds are taken in convenient sizes. Seeds should be treated with carbendazim @ 2 g/kg of seed. Spinach seeds more than a year old rarely germinate over 80%. Older seed is even less viable and germinates more slowly and irregularly. Seeds are either broadcast or sown in lines at 1.0-1.5 cm deep and 35 cm apart and covered with a thin layer of soil. After germination, thinning is done to retain plants in 10-12 cm spacing within each row. Closer spacing can stress plants and cause them to go to seed (bolt) sooner.
Spinach should be sown in the first week of October and can be repeated till the middle of December. Seeds should not be sown during spring and summer since it results in early bolting. In spinach, half of the plants produce male flowers and are poor in growth. These plants are to be uprooted as and when noticed. Hence, a little higher seed rate than that prescribed for palak is recommended. Spinach is usually direct seeded in rows using either precision methods and coated seed or regular drilled uncoated seeds. In some areas, spinach is simply broadcast on beds. The rate of germination fluctuates widely depending upon methods of seeding besides the risk of damping off.
Spinach seed is sown fairly shallow 1.0-1.5 cm ranging from slightly above permanent-wilting to field capacity. It is customary to schedule seedings to accommodate the daily capacity of harvesting equipment to ensure a steady flow of product at harvest. It is not customary to thin spinach stands.
Nutrition
Being a leafy vegetable, spinach requires higher doses of N for increasing leaf yield. Along with land preparation, farmyard manure @ 25 tonnes/ha is incorporated into the soil. About 80-100 kg N, 60 kg P₂O, and 60 kg K₂O/ha are required. The full dose of P₂O, and K₂O, and one-fourth dose of N are appl as basal dressing. The remaining quantity of N is applied in various splits (20-25 kg N/ha each) after every cutting, along with weeding and hoeing.
Irrigation
Good soil moisture is essential for the proper germination of seeds. Pre-sowing irrigation is advised. Later irrigations depend on the season and soil conditions. The crop requires a constant and uniform supply of water to obtain a good crop of high quality. During spinach production, the soil should never be allowed to dry out. Moisture fluctuations will cause leaves to become tough with slow leaf development, and contribute to off-flavors. Usually, irrigation is done at 4-5 days intervals in summer and at 8-10 days intervals in winter. Mulch around the plant also helps conserve soil moisture and reduce weed growth.
At a moderate temperature of 16°-21°C, leaves become lush green, containing more sugar and dry matter which ensure good quality. At a temperature of 25°C and above, leaves become less succulent, yellow and contain less sugar and dry matter owing to bolting tendency.
Aftercare
Thinning of overcrowded seedlings is essential to maintain the required spacing between plants. Weeding, hoeing, and earthing-up are important intercultural operations. Hand weeding is advocated in the early stages. After every cutting, weeding and hoeing should be done.
Seed production
Spinach is a cross-pollinated crop and pollen grains are carried by the wind. To provide an isolation distance of 1,500 to 3,000 m for stock seed. Seeds of Virginia Savoy are produced in hills and smooth leaved varieties in plains. It produces seed stalk in 65 days and seeds can be harvested in 180 days. Seeds are produced in female and monoecious plants. Extreme males do not bear any seed. The existence of different sex forms offers scope for the production of F, seeds in spinach. Seed yield is 900 1,000 kg/ha.
Flowers vary from 6-12/cluster but do not develop all at the same time. Male plants bolt and flower earlier than female plants, and die soon after flowering. Flowers may be staminate, pistillate or hermaphrodite, and remain receptive for a week or longer.
Normally, long days in combination with warm weather (above 25°C) are favorable for seed stalk formation. Photoperiodic response in spinach can be altered by low-temperature treatment. Exposure of plants to 10-15°C for a month can induce flowering even in short-day conditions.
Diseases and pest
Diseases
Damping-off and root rot (Fusarium oxysporum, Rhizoctonia solani, Pythium spp.): Poor germination rate of seeds; death of newly emerged seedlings; stunted; yellow plants, particularly lower leaves; poor growth, wilting, and collapse of older plants; roots may be water-soaked and discolored brown or black; necrotic lesions may girdle tap roots. Symptomatic plants are often found in low-lying areas of the field or garden where water accumulates; disease symptoms are similar to symptoms caused by overwatering plants. To manage the disease, sow the seed in well-drained soils; carefully manage irrigation to avoid saturating soil; use seed that has been treated with fungicide; avoid sowing spinach successively in the same location.
Downy mildew (blue mold) (Peronospora farinose): Initial symptoms of the disease are yellow spots on cotyledons and leaves which enlarge over time and become tan in color with a dry texture; purple fungal growth is present on the underside of leaves; severe infestations can result in curled and distorted leaves. Disease emergence is favored by moisture. oil and cool temperatures. To manage the disease use plant varieties which are resistant to the disease; application of appropriate fungicides to protect the plant if applied before infection begins; practice 3-year crop rotations and hot water treatment of seed.
Fusarium wilt (Fusarium oxysporum): Yellowing of older leaves; plants reaching maturity early; reduced seed production or death of plant before seed production takes place; vascular system of older plants may have a dark discoloration; seedlings may develop symptoms similar to damping off where cotyledons wilt and seedling dies; black lesions may be present on roots. The fungus can survive on seed and can be spread to previously uninfested fields avoiding spinach sowing in soils known to be infested with Fusarium or where spinach has been planted the previous year; planting early protect the seedlings from the disease due to lower soil temperatures, which are less favorable to the pathogen; avoiding water stress to plants during flowering and seed set. Do not sow the seed when the soil temperatures are high (mid-June to late August). Recommended fungicides can control the disease effectively.
Insects
Spinach leaf miner: The adult is a slender grey fly 4 mm long frequently seen hovering over the host plants. Small green or white maggots feed inside the leaves, forming blotches. There are several generations a year; pupae overwinter in the soil. Flies lay eggs on the undersides of the leaves. Larvae enter the leaves, feed until mature, then drop to the ground, pupate, and emerge as flies. Colorless blotches with a silvery overcast are formed by the larvae mining between the surfaces of the leaves. This makes the crop unmarketable. Heavy infestations stunt growth.
Recommended insecticides should be applied when mining damage is first observed. Two to three treatments at 10 days intervals may be needed. Early in the season infestations may be suppressed by destroying infested crop residues and weeds. In large commercial fields, leaf miner has not been a problem.
Aphids: Aphids are small, soft-bodied, slow-moving insects. They are often found in large colonies on the undersurface of leaves. A colony consists of winged and wingless adults and various sizes of nymphs. Aphids may be black, yellow, or pink, but most are in various shades of green. Aphids feed by sucking plant sap. Saliva injected while feeding may carry plant viruses or may be toxic to the host plant. Feeding by large numbers discolors foliage, and curls leave. The plants may be covered by a sticky substance, honeydew, which is excreted by the aphids.
Spray only if aphids are so numerous as to cause wilting of leaves during dry weather. Predators such as ladybird beetle (colored orange with black stripes or spots) and their larvae (black or purple with orange or white markings) usually control severe attacks of aphids.
Spinach crown mite: Leaves are deformed; with small holes in newly expanding leaves; mites are tiny and transparent, living deep in the crown of the spinach plant; damage can be done to newly emerged seedlings or to older plants. Mite infestation is favored by soils with high organic content and by cool, wet weather conditions. Destroy crop debris immediately after harvest; application of appropriate acaricide may be required if mites are damaging and weather conditions are cool and wet.
Harvesting and post-harvest management
Spinach yield varies from 80-100 q/ha. The plants may be hand-harvested whenever the leaves are large enough to use (a rosette of at least five to six leaves). Cut the plant at, or just below, the soil surface. Spinach is of the best quality if cut while young.
To maintain high quality in this highly respiring product, the crop must be quickly hydro-cooled or vacuum cooled to 0°C and held at that temperature with very high RH to prevent shriveling. Controlled atmosphere storage using 10% CO, deters yellowing of spinach for up to three weeks at a temperature of 5°C. Spinach can be held at 2°C for three or more weeks, the quality is not likely to be acceptable when the product is stored even half that time. To be fully acceptable spinach must remain turgid and essentially damage-free.
At home or in storage do not store spinach or other leafy vegetables along with ethylene emitting fruits or horticultural produce, it will cause yellowing of the leaves and impair the produce.
