Imagine stepping into your greenhouse on a frigid winter day, surrounded by snow-covered landscapes, yet harvesting crisp, vibrant lettuce leaves to enliven your meals. This vision is entirely achievable with proper greenhouse lettuce cultivation techniques. This comprehensive guide explores every aspect of greenhouse lettuce production, from varietal selection to daily maintenance, empowering you to establish a productive and healthy lettuce garden.
Compared to open-field cultivation, greenhouse lettuce production offers significant benefits:
Planting can commence whenever greenhouse (and soil) temperatures remain between 4-29°C (39-84°F). Maintain temperatures above freezing but avoid excessive heat.
Direct Seeding:
Sow clusters of lettuce seeds every 20-40 cm (8-16 inches) in rows spaced 30 cm (12 inches) apart, or broadcast seeds for later thinning. Precise spacing depends on lettuce type: loose-leaf varieties require 10-20 cm (4-8 inches), while heading types need 20-40 cm (8-16 inches).
Transplanting Seedlings:
Distribute seeds on container soil surfaces, covering lightly with fine soil. Lettuce seeds require light for germination, so avoid deep planting. Water gently with a spray mechanism to prevent seed displacement. Maintain soil temperature at 18-21°C (65-70°F) for uniform germination, using heating mats if necessary.
Lettuce thrives in greenhouse environments, particularly during transitional seasons. Recommended greenhouse varieties include:
While lettuce matures quickly (often within a month), temperature fluctuations can trigger premature bolting. Maintain optimal conditions:
Temperature Management: Keep greenhouse temperatures between 10-21°C (50-70°F). Night temperatures of 7-13°C (45-55°F) promote vigorous growth. Although lettuce withstands brief exposure to 35°C (95°F) or light frosts, prolonged extremes require protective measures like insulation covers or supplemental heating.
Water Requirements: Maintain consistent soil moisture throughout all growth stages. Use fine mist irrigation for seedlings, providing approximately 2.5 cm (1 inch) of water weekly. Shallow-rooted lettuce demands continuous moisture for tender leaf production.
Soil Conditions: Lettuce flourishes in organic-rich, well-drained loam with pH 6.0-7.0. Incorporate compost into the top 5 cm (2 inches) of soil before planting.
Light Exposure: Provide minimum six hours daily sunlight. In winter, supplement with grow lights to ensure adequate illumination.
Lettuce may encounter pests (earwigs, cutworms, aphids) or wildlife (groundhogs, rabbits) in inadequately secured greenhouses. Mature leaves often develop bitterness, so harvest when leaves reach usable size but remain tender. Overwatering can promote rot—monitor plants regularly and adjust irrigation accordingly. Install shade cloth during summer to delay bolting.
Harvest in early morning for peak freshness. For romaine and butterhead types, either cut entire heads at the base or pick outer leaves individually. For baby leaf varieties, use the "cut-and-come-again" method by making clean cuts above the crown to encourage regrowth. Consume immediately or refrigerate for up to 10 days.
Can I grow lettuce in summer greenhouses?
Yes, though in hot climates, greenhouse temperatures exceeding 32°C (90°F) may induce bolting. Without cooling systems, outdoor summer planting may be preferable in such regions.
How long does lettuce take to grow?
Baby leaf varieties mature in about 30 days, while heading types require 60-70 days. Most lettuces can be harvested early for baby greens.
When is the best time to start greenhouse lettuce?
Begin autumn plantings in most climates, using succession planting to maintain supplies through spring or until temperatures become unfavorable.
