Cucumbers are often grown in greenhouses to prevent insect and disease problems that occur when cucumbers are grown outdoors. The growing requirements for greenhouse cucumbers are different because temperature, level of soil nutrients and light levels must be sufficient to grow healthy plants. However, bees, important for pollinating the plants, are usually not present in a greenhouse. Therefore, purchase seed from European cucumber varieties, also known as all-female, or gynoecious, varieties because they produce fruit parthenocarpically, or without pollination.
Take a soil test to find out what amendments are needed for maximum production of cucumbers in the greenhouse. For assistance, contact the local county agricultural extension office. They will not only give you information on the correct way to take a soil test but where to send the sample once it is collected. It usually takes three to four weeks to receive the soil test results.
Apply all soil amendments recommended from the soil test along with a 1- to 2-inch layer of compost over the surface of the planting area inside the greenhouse. Work the amendments and compost into the top 6 inches of soil using a shovel or a hoe. Rake the planting area smooth.
Prepare the planting containers. It is best to start the cucumber seeds in planting containers rather than the ground, because the type of cucumber seed used in greenhouse production is expensive and there is less chance of seedlings being attacked by insects or fungal diseases.
Fill individual planting containers suitable for holding one plant each with a soilless potting medium. A soilless potting medium contains sterilised planting material along with a wetting agent and weak solution of fertiliser. Do not use garden soil or unsterilised potting soil that may contain fungal spores or insect eggs. The pots should be at least 3 inches deep and 2 inches by 2 inches wide. Some pots suitable for starting cucumber seed are biodegradable and can be planted directly in the ground.
Plant seeds 1/2 inch deep in the planting containers when daytime temperatures in the greenhouse are 26.6 to 29.4 degrees C. and nighttime temperatures are 18.3 to 23.8 degrees C. Keep the seeds moist, but not waterlogged, during the growth process. They should germinate, or sprout, in about three days.
Relocate the plants to the permanent planting bed inside the greenhouse when they have two sets of true leaves. Plant at the same depth as they are planted in the container. Be very careful not to disturb the roots while transplanting. Space the plants 2 feet apart. Rows should be 3 to 4 feet apart.
Keep the soil around the plants moist, but not wet, during the entire growing period. Do not allow the foliage and fruit to get wet while watering. If growing the vining type instead of the bush variety, provide support with a trellis or other device during the growing period. Most cucumber varieties begin to produce fruit within 60 days of planting.
Some varieties of European cucumbers suitable for greenhouse production are Mustang, Fertilia, Corona, and Bella.