How to Grow Cucumbers in a Greenhouse

Greenhouse cucumbers are a different crop from garden cucumbers. Parthenocarpic (seedless, self-fertile) varieties bred for greenhouse production climb aggressively, set fruit without pollination, and produce heavy yields on a single vertical stem trained up a string trellis. With proper management, a single greenhouse cucumber plant produces 20 to 40 fruit over a 3 to 4 month season.

Variety Selection

Choose parthenocarpic greenhouse varieties — not garden or field types. Parthenocarpic cucumbers do not require pollination and produce seedless fruit with thin skin and mild flavor. Popular varieties include Tyria, Corinto, Picolino, and Socrates. English (long) cucumber varieties are the classic greenhouse type; mini or snack cucumbers (Picolino, Katrina) are increasingly popular for direct sales and home use.

Avoid pollinated garden varieties in the greenhouse. Without reliable bee activity (difficult to achieve indoors), pollinated varieties produce misshapen or bitter fruit. Worse, if pollinated varieties cross-pollinate with parthenocarpic types via wind or stray insects, the parthenocarpic fruit develops seeds and becomes bitter.

Training and Trellising

Greenhouse cucumbers are trained to a single stem on a string trellis — identical to the tomato string trellis system. Remove all side shoots (laterals) from the main stem up to the overhead wire. Allow the growing tip to drape over the wire and hang down 2 to 3 feet. Fruit develops on the main stem at each leaf node. This single-stem umbrella training system maximizes air circulation and makes harvesting easy.

Alternatively, train laterals on a horizontal wire system: allow side shoots to grow horizontally along wires spaced 12 inches apart on a vertical trellis. Pinch each lateral after 2 to 3 leaves. This method produces more fruit per plant but requires more space and management.

Climate Requirements

Cucumbers are heat-lovers. Optimal day temperature: 78 to 85°F. Optimal night temperature: 65 to 70°F. Minimum night temperature: 60°F — below this, growth stalls and fruit quality declines. Cucumbers need high humidity (70 to 80 percent) for best growth, which most greenhouses provide naturally. Unlike tomatoes, cucumbers do not benefit from a large day-night temperature swing — they prefer relatively warm, stable conditions around the clock.

DLI requirement: 20 to 30 mol/m²/d for maximum production. This is among the highest of common greenhouse vegetables. In northern greenhouses, supplemental lighting extends the productive season by 2 to 4 weeks on each end.

Watering and Feeding

Cucumbers are heavy water consumers — a producing plant may need 1 to 2 liters of water per day in warm greenhouse conditions. Drip irrigation is essential. Never let the growing medium dry out; water stress causes bitter fruit, flower abortion, and fruit cracking. Feed continuously with a balanced hydroponic nutrient solution or fertigate with a water-soluble fertilizer at every watering during production.

Harvest fruit when they reach the appropriate size for the variety (typically 6 to 8 inches for minis, 12 to 14 inches for English types). Do not leave mature fruit on the plant — unharvested fruit signals the plant to stop producing new flowers. Harvest every 2 to 3 days for continuous production.

Pest and Disease Management

Powdery mildew is the most common cucumber disease in greenhouses. White powdery patches appear on older leaves and spread rapidly in humid, poorly ventilated conditions. Prevention: maintain good air circulation with HAF fans, remove lower leaves as they age, and avoid wetting foliage during watering. If powdery mildew appears, remove affected leaves immediately and increase ventilation. Biological fungicides containing Bacillus subtilis provide some preventive protection.

Aphids and whiteflies are the primary insect pests. Deploy Aphidius colemani wasps for aphid control and Encarsia formosa for whiteflies as part of a preventive IPM program. Spider mites can appear in hot, dry greenhouse conditions — release Phytoseiulus persimilis at the first sign of stippled leaves. Cucumber beetle, a major outdoor pest, is rarely a problem in enclosed greenhouses.

Succession Planting for Continuous Harvest

Greenhouse cucumbers produce heavily for 8 to 12 weeks before vine quality and yield decline. For continuous season-long production, start a second set of plants 6 to 8 weeks after the first transplanting. When the first planting declines (smaller fruit, slower production, increased disease pressure), remove it and shift to the second planting, which will be entering peak production. This relay approach provides uninterrupted cucumber harvests from April through October in most greenhouse environments.

Train the second planting on the same trellis infrastructure — simply cut old twine and hang new strings for the new plants. The turnover takes 1 to 2 days: remove spent plants, sanitize the growing containers, refresh the potting mix, transplant new seedlings, and reattach twine to the overhead wire. This relay system is the standard approach in commercial greenhouse cucumber production, where continuous supply is essential for maintaining market relationships and meeting weekly delivery commitments.

Start succession seedlings in propagation trays with heat mats 4 weeks before the planned transition date. Transplant into prepared containers the same day you remove the spent first planting. By the time the second planting reaches the trellis and begins fruiting heavily, you will have experienced only a 1 to 2 week reduction in harvest volume — barely noticeable at the hobby scale and easily managed at the commercial scale with proper planning. The key to successful succession planting is not the transition itself but the advance preparation — having seedlings ready, containers cleaned and filled, and trellis twine pre-cut so the changeover happens in a single focused morning rather than dragging out over a disruptive week. Planning this transition in advance avoids any gap in production.