Summary of Lettuce Growing Guide
In a few words, we start sowing indoors and transplant in the field or greenhouse, in most regions after the first frost. For the cultivation of 1 hectare, we need 28-31 oz. (800-900 grammars) of seed. We sow the seeds in seedbed/ pots at a depth of 0,17 inches (0,4-0,5 cm) and place them in a room with plenty of sunlight. We keep the soil moist. It is important to reserve the ground moist, but not irrigate excessively, because our seeds will probably rot and will not germinate. Some producers harden the young seedlings before transplanting them in the field. We transplant the lettuce in the field after the last frost. We choose an area with well-drained soil, free from stones and roots. Some producers also sow the lettuce seeds directly in the field, but this method is not recommended for high soil temperatures. Lettuce seeds are genetically programmed to go dormant above a certain temperature.
Lettuce plants prefer plenty of sun and thrive in soil rich in nitrogen and humus. In most cases, we plant lettuce leaving a distance of 8-12 inches (20-30 cm.) between plants and 20-23 inches (50-60 cm.) between rows. In a field of 1 hectare (10.000 square meters), we transplant about 50.000 plants. We irrigate frequently. Three weeks after transplanting, we may add a fertilizer that can boost the plants’ development, although lettuce is definitely not a heavy feeder (ask a local licensed agronomist). However, lettuce is a demanding crop in terms of farmer’s attention and time. Many farmers monitor the crop every day, checking soil moisture, pests, diseases and general crop health. In most cases, we harvest 60 – 90 days after sowing, depending on the variety. It is better to cut the lettuce in the morning. The average yield is 20-40 tons per hectare.
Lettuce Soil Requirements
Lettuce is a plant that thrives in nutrient-rich, well-drained soil. It is essential to perform a proper field preparation before sowing the seeds or transplanting the young seedlings. Experienced farmers report that it is helpful to till the soil and apply compost or well rotted manure normally one week before transplanting or direct seeding. In most cases, lettuce prefers a fertile soil with a pH ranging from 6 to 6,8. In order to have thriving plants and good yields, farmers prefer to keep the soil constantly moist. Growers shall perform a soil analysis before planting. It is recommended to consult a local licensed agronomist in order to form a rational field preparation plan.
Lettuce Water Requirements
Lettuce plants have a shallow root system. They normally prefer smaller but more frequent irrigation sessions. During hot summer months, we may need to irrigate lettuce plants everyday and maybe put a shade upon them. If we don’t regularly irrigate our plants during this season, lettuce plants will suffer from heat and bolting can be an issue (the plant starts to produce seeds). Consequently, lettuce leaves may become bitter. Bolting is generally irreversible and those plants cannot be marketed. Most farmers use sprinkler or drip irrigation systems. In order to keep the soil constantly moist, farmers may apply a thin layer of mulch to the ground (ask your local licensed agronomist). Sudden deviations in soil moisture will deteriorate plant’s growth.
It is highly recommended to water lettuce plants early in the morning or late in the afternoon. It is essential to avoid excessive watering that may result in disease outbreaks and root rot. Keeping the soil moist is the key to grow healthy lettuce.
Lettuce Planting and Spacing – Seeding rate and Planting Distances
In general, lettuce plants need cool weather to thrive. We should focus on planting seeds in the appropriate time window, depending on when we want to harvest them.
Depending on the variety, lettuce can grow in a temperature between 45 to 64 °F ( 7-18 °C). Under certain circumstances and special handling (for example shades), lettuce can grow even in 84 F° (29 °C). When we decide to plant lettuce in spring or fall, the perfect location is a sunny area. On the contrary, when we decide to plant in late summer, lettuce requires sufficient protection from the sun. This can be provided by shades. When the weather starts to become cooler, we may remove the shades and let the young plants receive the sunlight they need.
We can direct seed our plants or transplant them. In direct sowing, we plant lettuce seeds in rows, in a depth of ¼ inch (0,6 cm). Furthermore, we can sow by broadcasting the seeds for a wide row planting. In most cases, experienced farmers claim that spring frosts and summer heat injure their plants. To avoid that, they normally start growing their plants indoors. Growers normally start seeding indoors before the frosts begin. Two weeks after the frost, they can transplant them outdoors. Lettuce plant is transplanted with its soil block attached. Farmers may follow the same measure against summer heat. During summer heat, they plant lettuce seeds indoors. Then, when the weather gets cooler, they usually transplant them outdoors.
In order to achieve good growth and maximize their yields, farmers may take into consideration the following factors.
- Seeding Rate: 800-1000 gr (28 to 35 oz.) of seeds per hectare
- Number of plants per hectare: 50.000-60.000 plants
- 1 hectare = 2,47 acres = 10.000 square meters
- Space between rows is 11-23 inches (27-60 cm) and space between plants in the rows is 7-12 inches (18-30 cm)
- Lettuce seeds are small and require a depth of ¼ inch (0,6 cm)
- We can use thinning once the seeds are germinated. We may continue thinning until there is sufficient space between lettuce heads. A common pattern is leaving at least 7 inches (18 cm) between each plant, but this also depends on the variety.
- Farmers may seed other plants between lettuce rows (intercropping). Rows of garlic can help in aphid control, while sweet corn or peas may provide natural shade.
- Farmers may consult their local licensed agronomist in order to schedule a proper growing plan.
Lettuce Fertilizer Requirements
It is essential to perform a soil analysis before any fertilizer application. No two fields are the same nor can anyone advise you on fertilizer requirements without knowing your crop history and the results of your soil analysis. In general, lettuce reaches maturity fast, so many farmers make just one fertilizer application about 20 days after transplanting. In other cases, lettuce crop is established as a rotation crop between heavy feeders (for instance broccoli), so in this case they may apply no fertilizer at all. However, this method may involve problems with diseases.
In general, fertilizer application often takes place three weeks after the plants are transplanted into their final position. In many varieties, farmers let the lettuce grow in height before they apply any fertilizer. Many farmers use a well balanced fertilizer, consisted of essential nutrients, such as nitrogen (N), potassium (K) and phosphorus (P), usually in the form of granules. Experienced farmers claim that granular fertilizers can be applied in the form of 10-10-10 (N-P-K) or 5-5-5 (N-P-K) mixtures. We may apply the granules to the ground around lettuce plants. It is crucial that the granules don’t come in touch with the young plants, because there is a risk of burning them. After applying fertilizers, irrigation is usually required.
In other cases, farmers prefer to use fertigation (injection of water soluble fertilizers in the drip irrigation system). It is suggested that we follow manufacturer’s instructions before we inject any water soluble fertilizer.
Finally, some farmers apply KNO3 at a rate of 200 kg per hectare about 35 days after transplanting (1 hectare = 2,47 acres = 10.000 square meters and 1 ton = 1000 kg = 2200 lbs.).
Organic farmers may apply well-rotted manure and plow the soil two weeks before planting. Organic manure helps in weed control and preserves soil moisture.
However, these are just common patterns that should not be followed without making your own research. Every field is different and has different needs. You may seek advice from a licensed agronomist after conducting a soil analysis.
Lettuce Pests and Diseases
It is necessary to know our crop enemies and form in advance an environmentally friendly approach in order to tackle them. We can consult a local licensed professional for a proper control of lettuce pests and diseases. The most common lettuce pests and diseases are listed below.
- Aphids. They are one of the most common enemies of leaf vegetables. Adults and nymphs feed on plant juices and also attack stem, flowers and leaves.
- Slugs. Slugs love to crunch the lettuce leaves, something that results in large holes and product that cannot be marketed. If they are let to reproduce freely, they may destroy the entire crop in short time.
- White Mold. It is a fungal disease, also known as sclerotenia. It affects a large variety of plant species, including lettuce. We can identify it by looking at the stems. Stems appear to be discolored and wilted.
- Bottom rot. It is a fungal disease that mostly attacks mature plants. It is caused by Rhizoctonia solani.
- Downy mildew. It is a disease caused by Bremia lactucae, causing yellow necrotic spots on older leaves.
Pest and Disease Control
The best way to control pests and diseases is always prevention rather than intervention. Lettuce growers shall take into consideration the following measures.
- Use of certified seeds and seedlings is necessary.
- Use of disease resistant varieties may prevent disease outbreaks.
- Encourage natural pest enemies (such as ladybugs) can be helpful in some cases. Ask your local licensed agronomist.
- Row covers are often used to protect lettuce plants from pest attacks.
- Nets can protect our crops from various pests.
- Avoid excessive application of fertilizers.
- Weed control and crop rotation methods can be applied against some diseases.
- Chemical control measures is allowed only after consulting a local licensed agronomist.
As a general rule, lettuce sowing to harvesting can take from 65 to 130 days (depending on the variety). In most cases, lettuce can be harvested between 30 and 70 days after transplanting. The proper time for harvesting our plants depends not only on different varieties, but also on local conditions (weather, planting distances, preferred market weight, fertilization etc.).
Important things about Lettuce Harvesting:
- It is recommended to avoid harvesting overmature plants. Their leaves have a bitter taste, so it is preferred to harvest them when they are still young, just before maturity.
- Leaf lettuce can be harvested by removing its outer leaves. Therefore, inner leaves (close to the center of the plant) can continue to grow.
- We must regularly check our field looking for plants that are ready for harvesting.
- The ideal time to harvest lettuce is very early in the morning, before the sun rises. According to some lettuce farmers, this time of the day is perfect, because lettuce plants are not exposed to intense sunlight.
- After harvesting, farmers store the lettuce in a cold but not freezing place.
Lettuce Yield per Hectare
The average lettuce yield per hectare is 20-40 tons. Keep in mind that 1 ton = 1000 kg = 2200 lbs. and 1 hectare = 2,47 acres = 10.000 square meters. Experienced lettuce farmers in areas with proper climate can harvest 20-40 tons per hectare multiplied by 2-4 crops a year. Of course, such high yields can be accomplished from experienced farmers after several years of practice.
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