Summary of Spinach Commercial Growing Guide
In a few words, nearly all commercial spinach growers sow spinach seeds (mostly hybrids) directly in the field during fall or spring. Especially when growing spinach for the processing market, most commercial growers then thin the plants (they remove some plants from the field, so as to leave fewer plants and improve aeration). Fertilization, Sprinkler Irrigation, and Pest Management are applied in most cases. Time to harvest depends on whether we grow Spinach for Fresh or Processed Market. In many cases, spinach plants targeting fresh market are harvested in one cut (the whole plant is destroyed) about 40-55 days from seeding. On the contrary, spinach leaves that target processed market are harvested at about 60-80 days from seeding. In many cases, both the fresh and processed plants (but mostly the processed plants) are let to grow and regenerate after the first harvesting session, so that the producers can harvest a second cut.
Spinach Soil Requirements
Spinach can grow well in the average soil, but it will thrive in soil rich in organic matter. In general, soil type and pH rarely become a restrictive factor when growing spinach. However, spinach has been reported to thrive in sandy loam soils with pH 6,5 to 6,8. In cases of severe P deficiencies, farmers may apply P2O5 at a rate of 50kg per hectare some days before seeding. Keep in mind that each field is different and has different needs. Growers should perform a soil analysis before planting. They can also seek advice from a local licensed agronomist in order to form a rational field preparation plan. Some farmers also apply well-rotted cow manure and plow well some days before seeding, in order to restore N levels. However, keep in mind that these are just some common patterns that you should not follow without making your own research.
Spinach Water Requirements
Spinach plant has a relatively shallow root system. As a result, the plant prefers smaller and more frequent irrigation sessions, in order to produce an acceptable yield. As a rule of thumb, farmers should focus on keeping the soil moist during the growing period. Experienced farmers claim that keeping the soil constantly moist, helps plant in two ways. On the one hand, the plant will be able to absorb the necessary water. On the other hand, this will keep soil temperature low, resulting in better spinach growth.
Spinach tends to bolt into seeds when the weather is too hot. In this case, plants are genetically set to devote their resources producing seeds rather than leaf development. Therefore, the product cannot be marketed. In most cases, three to four irrigation sessions per week are used during the first two weeks. It is highly suggested to irrigate our crops early in the morning or late in the afternoon. This will prevent water evaporation from the sun’s heat.
More than half of world production is irrigated through sprinklers. However, in some circumstances, extensive use of sprinkler irrigation favors the outbreak of leaf spotting diseases.
Spinach Planting; How to grow healthy and thriving spinach
As mentioned earlier, spinach generally needs cool weather, so most growers start growing it during early spring or late fall. Many farmers like to seed spinach six weeks before the last spring frost. In areas with cool spring, we can seed every ten days until late spring (mid-May). In the case of seeding spinach in warm climates, we may also sow them in the shade of tall crops, such as wheat, beans or corn.
Depending on the variety, spinach can grow in a temperature between 50-70 °F degrees (10-21 °C). When we decide to plant spinach in spring or fall, the perfect location is a sunny area with light shade and well-drained soil. During winter, we can protect our plants with cold frames or cover them with mulch. Farmers often remove these protection measures only after temperature reaches 40 °F degrees (5 °C).
In most cases, spinach is sown directly into the field. Farmers can sow spinach seeds (mostly hybrids) directly to the ground in rows or by broadcasting them. The plants need sufficient space between them to grow. In direct sowing, we plant our seeds in rows, in a depth of 1-1,18 inches (2,5-3 cm). For continuous production, we may sow every 10-15 days.
In order to achieve good growth and maximize their yields, growers may take into consideration the following factors.
- Seeding Rate: 40 to 60 lbs (20 to 30 kg) of seeds per hectare.
- Seeds germination will be better in temperatures 41-68 °F (5 to 20 °C)
- Spinach seeds require a depth of ½ to 1 inch (1 to 2,5 cm), covered lightly with soil.
- Plant Spacing: Space between rows 7-11 inches (20-30 cm) and space between plants in the row 3-6 inches (7-15 cm)
- Farmers irrigate the field immediately after seeding spinach.
- Companion Planting is often used. Farmers can sow other plants between the rows of spinach plants. Cauliflower, Onion and Celery are mostly used.
- Thinning is used, in order to encourage plants to produce a great leaf surface. This is the most common technique when we grow spinach for the processing market.
- Regular but not excessive watering will ensure soil moist.
- Weed Management cannot be ignored. Weeds not only compete with spinach in terms of nutrients and access to sunlight, but they will also prevent proper aeration, thus creating the perfect conditions for disease outbreaks.
- Farmers can seek advice from local professionals (licensed agronomists) in order to schedule a proper plan to grow healthy and high-quality spinach.
Nutrient Management in Spinach Crops
Spinach can produce leaves in the average soil, but it will thrive in nutrient-rich soil. Many experienced farmers apply a mix of compost and phosphorus fertilizer into the soil, a few days before planting the seeds. In cases of severe P deficiencies, farmers may apply P2O5 at a rate of 50kg per hectare some days before seeding (ask a licensed agronomist). Keep in mind that 1 hectare = 2,47 acres = 10.000 square meters.
A great number of farmers use fertigation, ie. injection of water-soluble fertilizers in the irrigation system. This way, they can boost production and save time by watering and fertilizing the plants simultaneously. It is suggested that we follow manufacturer instructions before we use any fertigation method.
Spinach is a leafy vegetable and we grow it in order to collect its leaves. As a result, in most cases, farmers may apply N and P during different stages of plant growth in order to maximize the total leaf surface. Spinach requirements in N are about 70-80 kg per hectare, depending on the type (savoy versus smooth). Many farmers also apply Ammonium Nitrate (N-P-K 20-0-0) at a rate of 50kg per hectare (ask your local licensed agronomist).
In the case of organic production, we may use organic fertilizer rich in nitrogen. Organic fertilizer application can take place once or twice while spinach plants are still growing. We may also use compost manure mixed with other sources (such as fish emulsions etc.). In most cases, organic manure helps in weed control and soil moisture conservation during the summer months. It is crucial that any type of manure doesn’t come in touch with the young plants, otherwise, we may have problems. After applying fertilizers, it is suggested to irrigate our crops.
Keep in mind that these are just some common fertilization methods that should not be followed without making your own research. Every field is different and has different needs. Conducting Soil Analysis and knowing your crop history is absolutely essential before applying any fertilization method. You may seek advice from a licensed agronomist.
Pests and Diseases
Unfortunately, spinach plants are often attacked by pests and they often suffer from diseases. Knowing our local crop enemies is essential in order to form an environmentally friendly approach and face them. Before taking action, farmers may consult a local licensed professional for proper control of spinach pests and diseases.
- Aphids; Aphid is normally the most common enemy of spinach plants. Adults and nymphs feed on plant juices. As a result, we end up with a product that cannot be marketed.
- Leaf miners; They mostly feed on the leaves.
- Slugs and snails; they both appear very often in soggy soil and attack the leaves. They can even eat the whole plant if we don’t face them properly.
- Mosaic virus; this virus can infect about 150 different types of vegetables and plants. We can identify it by the discoloration of the leaves. The infected leaves turn to have yellow and white spots. The plant stops growing in size and slowly dies.
- Downy mildew; It is a disease caused by the pathogen Peronospora farinosa. We can identify it by looking at the leaves. They appear to curl and have mold and black strains.
- Spinach blight; this virus infects leaves. Infected leaves stop growing in size and have yellow to brown color.
Pest and Disease Control
The best way to control pests and diseases is always prevention rather than intervention. Spinach growers shall take into consideration the following measures:
- The use of certified seeds is suggested. In most cases, farmers shall select hybrids that have resistance to bolting and Downy Mildew.
- Low germination of seeds or improper seeding rate will accelerate the negative effects of pests and diseases.
- Inadequate fertilization and/or Irrigation will accelerate negative effects.
- Chemical control measures are allowed only after consulting a local licensed agronomist.
- Crop rotation can be applied in order to control some diseases.
Time to harvest depends on whether we grow Spinach for Fresh or Processed Market. In most cases, spinach plants for fresh market are harvested in one cut (the whole plant is destroyed) about 38-55 days from seeding. On the contrary, spinach leaves that target processed market are harvested at about 60-80 days from seeding. In many cases, both the smooth and savoy plants (but mostly the smooth plants) are let to grow and regenerate after the first harvesting session, so that the producers can harvest a second cut.
In developed countries, spinach is mostly harvested through machines that are attached to tractors. These machines either collect the whole plant and destroy it (one single cut) or cut the leaves at a predefined height in order to encourage regeneration and a second harvesting session some days later. After collected, spinach leaves along with soil, dirt, and stones go through a series of webs, where spinach is isolated from foreign materials and collected.
In developing countries, spinach can also be harvested through hand scissors. Farmers either collect the whole plant (and thus destroy it) or collect a portion of its leaves in order to encourage the plant’s regeneration and harvest a second cut some weeks later. According to many experienced farmers, the ideal time to harvest our plants is early in the morning. By this way, we prevent sunlight exposure of the plant material.
Spinach leaves are usually available on the market immediately after harvesting, and the product may be offered fresh, frozen, canned or dried. Fresh spinach can be stored in the refrigerator for 7-10 days. In large commercial spinach farms, farmers cool immediately the harvested spinach leaves, in order to prevent product deterioration.
Spinach Yield per Hectare
The average spinach yield is 20-30 tons per hectare. Of course, such high yields can be accomplished by experienced farmers after several years of practice. In the case of multiple harvesting sessions of the same crop, we may expect 10-15 tons per hectare multiplied by 2 – 3 harvesting sessions.
Keep in mind that 1 ton = 1000 kg = 2200 lbs. and 1 hectare = 2,47 acres = 10.000 square meters.
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