How to grow lettuce leaves in a greenhouse? When to plant and how to care for them?

Growing lettuce in a greenhouse is a great way to get fresh and vitamin-rich greens all year round. Lettuce leaves are unpretentious, grow quickly and do not require complex care, but to get a quality harvest, it is important to comply with certain conditions. In this article, we will analyze the optimal planting dates, growing technologies, care nuances and plant protection from diseases and pests.

Optimal conditions for growing lettuce in a greenhouse

Lettuce is a cold-resistant crop, but it is demanding in terms of light, humidity and soil composition. To achieve high yields, it is necessary to observe several key factors:

• Temperature conditions: the optimum temperature for growth is +15…+20°C. At temperatures above +25°C, the leaves become coarse and premature flower stalk production is possible. At temperatures below +5°C, growth slows down, and at 0°C and below, the plant may die.
• Lighting: in winter, additional lighting (phytolamps) is required to maintain 10-12 hours of daylight. Insufficient light leads to stretching of plants and a decrease in the nutritional value of the leaves.
• Air humidity: 60–80%. High humidity is necessary to maintain the juiciness of the leaves, but excess moisture provokes the development of fungal diseases. To maintain the optimal humidity level in the greenhouse, it is recommended to use drip irrigation and regular ventilation.
• Soil: light, well-drained, with neutral acidity (pH 6.5–7.0). The best option is a mixture of garden soil, humus and sand in a ratio of 2:1:1. To improve the soil structure, you can add coconut substrate or vermiculite.

Advice: During the cold season, use infrared heaters or warm beds with bio-heating (horse manure, straw) so that the root system does not suffer from temperature changes.

Planting times: when is the best time to plant lettuce?

The timing of planting lettuce in a greenhouse depends on the climate zone, the type of greenhouse and the presence of heating:

• In heated greenhouses, lettuce can be grown year-round, from late fall to spring, before other crops have been planted. However, it is important to maintain stable temperatures and humidity levels to avoid stressing the plants.
• In unheated greenhouses, sowing is possible in early spring (February–March) and autumn (September–October), when the temperature does not fall below +5°C. During such periods, it is important to additionally insulate the soil using mulching and bioheating.
• For the conveyor method of growing, sowing is carried out every 10-14 days, which allows for the production of fresh greens without interruption. This method is especially convenient for farmers and commercial farms.

Tip: If you want to get an earlier harvest, use the seedling method - sow seeds in cassettes or boxes 2-3 weeks before planting in the ground. After 3-4 true leaves appear, the seedlings can be transplanted into a greenhouse.

Choosing a lettuce variety for a greenhouse

The right choice of variety determines the quality and quantity of the harvest. Leafy varieties are suitable for quick harvesting, while cabbage varieties produce dense heads, but require more time.

The best varieties for greenhouses:

Type of salad	Recommended varieties	Peculiarities
Sheet	Lollo Rosso, Oakleaf, Festivalny	It grows quickly, can be harvested by cutting leaves, and is resistant to bolting.
Cabbage	"Iceberg", "Kucheryavets Odesskiy", "Crispino"	Forms dense heads of cabbage, requires more time to ripen, and is less sensitive to temperature changes.
Romaine	"Parisian", "Romain Cos"	Dense elongated leaves, high nutritional value, long shelf life.
Oily	"Batavia", "The May King"	Delicate leaves, resistant to cold and lack of light, but requires more frequent feeding.

Tip: Leafy varieties ripen faster and can be grown all year round, while head varieties require more time and space. For a greenhouse, it is better to choose hybrid varieties that are resistant to bolting and diseases.

Technology of planting lettuce in a greenhouse

Soil preparation

The soil in the greenhouse should be fertile, light, well-drained and rich in organic matter. To prepare the soil, you need to take several important steps:

1. Digging and loosening: The soil is dug to a depth of 25–30 cm, removing weed roots and plant debris to prevent the development of pathogenic microorganisms.
2. Adding organic fertilizers: Before planting, it is recommended to add humus or compost (4–5 kg per 1 m²). If the soil is depleted, wood ash (200 g/m²) or vermicompost is added.
3. Acidity correction: Lettuce prefers a neutral pH level (6.5–7.0). If the soil is acidic, dolomite flour or lime (300–400 g/m²) is added.
4. Disinfection: A week before planting, the soil is watered with a solution of potassium permanganate (1 g per 10 l of water) or Fitosporin to destroy fungal spores and bacteria.
5. Formation of beds: Beds are made 80–100 cm wide with row spacing of 30–40 cm for ease of maintenance. The surface is leveled and loosened to improve air exchange.

Advice: To protect against root rot, you can add Trichodermin or Gliocladin - these are biological preparations that prevent the proliferation of pathogenic fungi.

Sowing seeds

Before planting, it is important to properly prepare the seeds, as this affects the germination and stability of the plants:

• Soaking: Seeds are kept in a growth stimulator (Epin, Zircon) for 12 hours to accelerate germination.
• Hardening: To improve resistance to temperature changes, seeds are placed in the refrigerator for 2–3 days at a temperature of +2…+4°C.

After preparation, the seeds are sown:

• The planting depth is 0.5–1 cm so that the seeds do not suffocate during germination.
• Planting scheme:
  • For leaf lettuce – 10–15 cm between plants, 15–20 cm between rows.
  • For cabbage - 25-30 cm between plants, 30-40 cm between rows.
• Sowing methods:
  • Row method - seeds are sown in furrows, then covered with a thin layer of soil.
  • Nest method – 3-4 seeds in one hole to obtain more powerful bushes.

After sowing, the beds are carefully watered with warm water (+20…+22°C) and covered with agrofibre or film to maintain humidity.

Tip: For uniform germination, use pelleted seeds - they contain nutrients and protection against fungi.

Caring for seedlings

After the emergence of seedlings (on the 5th-7th day), caring for the lettuce includes several important stages:

1. Thinning: When planting densely, lettuce is thinned out in the phase of 2-3 true leaves, leaving strong plants. Excessively dense planting leads to stretching and weakening of plants.
2. Top dressing: The first top dressing is carried out 10-12 days after the emergence of shoots. Use mullein infusion (1:10) or urea solution (10 g per 10 l of water). The second top dressing is carried out in the phase of 4-5 leaves with phosphorus-potassium fertilizers (15 g of superphosphate and 10 g of potassium sulfate per 10 l of water).
3. Watering: Water 2-3 times a week with warm water (not lower than +18°C). It is important to avoid getting water on the leaves to prevent the development of rot.
4. Ventilation: To prevent fungal diseases, the greenhouse is regularly ventilated. Optimum humidity is 60–80%.
5. Protection against pests: If aphids or slugs appear, use biological preparations (Fitoverm, Actofit) or infusions of garlic and tobacco.

Tip: To improve growth, you can use humate-based stimulants – this will help plants develop a strong root system faster.

Watering and fertilizing

Watering lettuce in a greenhouse

Lettuce is sensitive to both a lack and excess of moisture, so it is important to maintain the correct watering regime.

1. Watering frequency:
   • Young shoots are watered daily with small portions of water, especially in hot weather.
   • Adult plants require watering 2-3 times a week, depending on soil moisture and air temperature.
   • On hot days, watering may be required more often, but it is important to ensure that moisture does not stagnate.
2. Irrigation methods:
   • Drip irrigation is the best method of watering, providing uniform soil moisture without over-watering.
   • Watering under the root – used if there is no drip system. The water should be warm (+18…+22°C), it is better to water in the morning or evening.
   • Spraying - only used in very dry conditions, but avoid getting water on the leaves to prevent fungal diseases.
3. Soil moisture control:
   • Optimal soil moisture is 70–80%. If the soil dries out, the leaves become tough, bitter, and lose their juiciness.
   • Overwatering can cause root rot, mold, and fungal infections.

Tip: In greenhouses with high humidity, it is recommended to periodically loosen the soil to improve aeration and prevent water stagnation at the roots.

Top dressing

Lettuce requires a balanced diet, as it quickly accumulates nutrients from the soil. Lack or excess of fertilizers can affect the taste and quality of the leaves.

1. First feeding (phase 3-4 leaves):
   • Nitrogen fertilizers (stimulate the growth of greenery):
     • Infusion of mullein (1:10 with water) – 0.5 l per 1 m².
     • Urea (carbamide) – 10 g per 10 l of water.
     • Green fertilizer (nettle infusion) – 1 l per 10 l of water.
2. Second feeding (before the formation of heads or when 5–6 leaves develop):
   • Phosphorus-potassium fertilizers (strengthen the root system and prevent bolting):
     • Superphosphate – 15 g per 10 l of water.
     • Ash (source of potassium and microelements) – 200 g per 1 m².
     • Monosuperphosphate – 10 g per 10 liters of water.
3. Organic fertilizers:
   • Biohumus – increases soil fertility.
   • Compost tea – improves soil structure and supplies plants with microelements.
4. Mineral complexes:
   • Complex fertilizer NPK (10:10:10) – provides balanced nutrition.
   • Calcium nitrate (5 g per 10 l of water) – prevents the development of blossom-end rot.
5. How to identify nutritional deficiencies?
   • Yellow leaves – lack of nitrogen.
   • Purple tint on the underside of leaves - phosphorus deficiency.
   • Pale leaves and weak stems indicate a lack of potassium.
   • Leaves quickly bolt - excess nitrogen.

Advice: Alternate organic and mineral fertilizers to avoid nitrate accumulation. Stop fertilizing 5-7 days before harvest to avoid excess salt content in the leaves.

Harvesting and storage

The timing of salad harvesting depends on its type and growing technology:

1. Leaf salad:
   • Cutting is carried out 30–40 days after planting, when the leaves reach 10–15 cm.
   • Harvesting is done selectively - first the outer leaves are cut off, leaving the central rosette for further growth.
   • Allows you to harvest several times from one plant.
2. Head lettuce:
   • They are harvested when the heads are fully formed (45–60 days after planting).
   • Trimming is done with a sharp knife, leaving 2–3 cm of the stalk.
   • If you leave lettuce in the garden for too long, it may start to bolt and lose its flavor.

Storage conditions:

• The optimal storage temperature is +2…+5°C at a humidity of 85–90%.
• Lettuce leaves will keep for up to 5-7 days in the refrigerator in airtight containers or damp paper.
• Head lettuce stays fresh for 10-14 days when stored in boxes with air circulation.
• Soaking before storage - the leaves can be immersed briefly in cold water, then dried and stored in bags with holes for ventilation.

Tip: To extend shelf life, you can use vacuum containers or micro-perforated film, which maintains an optimal level of humidity.

Growing Lettuce Leaves in a Greenhouse

Growing lettuce in a greenhouse is a simple and effective way to get fresh greens all year round. The main thing is to maintain the temperature regime, provide sufficient humidity and choose the right varieties.

Want to create ideal conditions for growing lettuce? Greenhouses from NovaTeplitsa provide reliable plant protection, create a stable microclimate and increase yields. Check out the models on our website and start growing lettuce with maximum efficiency!