Cucumbers generally grow more rapidly than tomatoes and produce earlier. They also require higher temperatures, which means they are generally grown as a spring or early summer crop. Daytime temperatures should be 80-85°F (nighttime 65-75°F). Soil temperatures should be at least 65°F. Lower temperatures will delay plant growth and fruit development.
Cucumbers are heavy feeders requiring 300-400 lb/a of P205. Similar quantities of potassium are required. Weekly feedings with a balanced fertilizer (20-20-20) will be required for maximum production. Never stress seedlings for water or nitrogen.
Plants are best started in individual containers. As seed are often very expensive, sow one seed per container (1/4 to 1/2 inch deep) in a sterile potting mix with the spiked end of the seed up (root will emerge facing down). Water, cover pots with clear polyethylene, and place in the shade. Plants will emerge in two to three days at 80-85°F. Remove plastic coverings when plants emerge and place them in full sun.
After plants have formed at least two true leaves, transplant them to their permanent location in the growing bed. Cucumbers will require 6-8 square feet of space per plant. Plants are generally spaced 2 feet apart in rows 3 to 4 feet apart.
Cucumber vines can be trained on plastic twine supported from horizontal support wires running the length of the rows (7-8 feet above top of bed). The base of the string can be anchored loosely to the base of the stem with a non-slip noose.
As the stem develops, it can be fastened to the string with plastic clips. Allow one stem to develop, removing all laterals and tendrils as they develop. Fruit buds should be removed from the first five leaf nodes. Thereafter, fruit can be allowed to develop, but continue to remove all laterals and tendrils.
After the stem reaches the horizontal support wire, it can be trained along the wire and then down another string suspended from the horizontal wire between the two plants in the row. The stem is then allowed to follow the string downwards to within 18 inches of the bed. It is then trained back up the original string with the stem forming a circle. Remove old leaves on the older part of the stem ahead of the developing stem terminal.
Fruit should develop at each node. Remember to remove all laterals and tendrils to encourage fruit production. Fruit production should continue for approximately 60 days.
Seedless (parthenocarpic) or all female (gynoecious) varieties are generally recommended for greenhouse cucumber production. These types generally produce higher yields and do not require bees for pollination. European seedless cucumbers are generally the most popular type of cucumber grown in the greenhouse. 'Mustang' is suitable for early or fall cropping and has potential for high total production. This variety has excellent fruit shelf life and color, with 12- to 14-inch fruit. 'Bronco' is suitable for very early spring or late fall cropping (low light conditions). It produces high quality fruit 12-14 inches long. Other popular varieties that have performed well include 'Sandra', 'Boneva', 'Daleva', 'Padex', 'Fertila', 'Factum', 'Femspot', 'Femfrance', 'Toska 70', 'Farbio', 'Corona', 'Sweet Slice', 'Radja', 'Bella', and 'La Reine'.
With good management, each plant may produce as much as 20-30 pounds of fruit over a four-month period. European varieties are generally harvested when fruit are 12-16 inches long and 3/4-1 pound in size. Fruit are often shrink-wrapped to prevent softening from moisture loss. Store fruit at 55°F with 80-90 percent relative humidity.
Seedless European greenhouse cucumbers are distinctly different from traditional field-grown cucumbers. Because of consumer expectations for field-grown cucumbers, greenhouse cucumbers may require some market promotion. Excellent selling points include their seedlessness, dark green color, mild flavor, and thin, tender skins that require no peeling.
Diseases. Gummy stem blight (Didymella bryoniae) is a fungus that occurs on all above-ground parts of the plant causing extensive damage to leaves, stems, and fruit. Light brown to black lesions occur on leaves, at nodes, and in pruning wounds. Leaf lesions eventually dry and fall from leaves. Stem lesions can crack at the soil line, producing an amber-colored gummy ooze, and can girdle the plant resulting in death. This disease also can occur as grayish-green water-soaked lesions on fruit beginning at the blossom end and can develop on fruit after harvest. Control by using steam sterilization of soil, good sanitation, crop rotation, and good ventilation. Avoid night temperatures below 60°F and overhead irrigation. Use preventative fungicides.
Powdery mildew (Sphaerotheca fuliginea and Erysiphe cichoracearum) fungus first appears as pale yellow leaf spots. The spots rapidly enlarge to fine cottony growth on the leaf surface. The spots also can occur on the stems and fruit. The fungus causes severe stress on plants as leaves yellow and die. Powdery spores produced on the leaf surface spread from plant to plant by air currents. Control through good sanitation, preventative fungicides, and resistant varieties.
Other diseases that can occasionally cause problems include various viruses (cucumber mosaic and watermelon mosaic), gray mold (Botrytis), damping-off, and crooking. Crooking is a physiological disorder often caused by temperature extremes, excessive soil moisture, and nutrition imbalances. Fruit will become excessively curved, reducing its market value.
Insects. Insect pests include whitefly, thrip, leaf miner, and other non-insect pests like two-spotted mites. Insects can gain entrance into the greenhouse through vents, doorways, openings in the greenhouse, and even on clothing and equipment. Regular plant inspections are important for immediate and effective control.
Lettuce is generally grown when light intensities are low and temperatures are cool. Plants prefer a daylight temperature of 60-65°F and a nighttime temperature of 50-55°F. High greenhouse temperatures will often result in spindly growth and seedstalk development in some varieties. A crop of lettuce can be scheduled between fall and spring tomato crops.
Lettuce usually takes about one month from seeding to transplanting. Days to harvest from seeding may vary from 12-15 weeks in mid-winter and from 8-10 weeks in early spring. Under poor light intensities a 9 x 9-inch spacing may be used, while a 6 x 6-inch spacing can be used in the spring as light conditions improve.
Lettuce is a poor feeder, but requires a high level of nutrition. Apply a balanced fertilizer before planting with weekly nitrogen feedings as needed.
Leaf and Bibb lettuce varieties are the most common types grown in the greenhouse. Popular leaf lettuce varieties include 'Waldmann's Dark Green', 'Grand Rapids', and 'Ruby'. Bibb lettuce varieties include 'Ostinata' and 'Salina'.
Other Greenhouse Crops
Other crops that have done well under greenhouse conditions include sweet peppers, eggplant, and herbs like basil. Popular pepper varieties include 'Cubico' (red), 'Locas' (red), 'Samanta' (yellow), and 'Doria' (yellow).
1 Resistance - ability of plants to restrict the activities of a specific pest. Tolerance - ability of plants to endure a specific pest or adverse environmental condition and continue to grow and produce a crop.