Greenhouse cucumbers need to be grown in a controlled, closed environment away from pollinating insects, with tropical conditions mimicked by high temperatures, humidity, and light. This type of cucumber plant is gynoecious or parthenocarpic, meaning that only female flowers are produced. If the flowers were to be pollinated, the resulting cucumbers would be bitter and oddly shaped.
A closed greenhouse system allows the gardener to produce greenhouse cucumbers while reducing disease and controlling growing conditions. Approximately 85 degrees F (29.4 degrees C) is the ideal temperature to germinate cucumber seeds, with 77 degrees F (25 degrees C) as the best temperature to grow maturing plants. Make certain that air circulation is available.
Cucumber seedlings might need light supplementation for adequate growth. Foot candles can be used to extend the daily light period up to 14 hours if necessary. This is typically more important in springtime or in areas where natural light conditions are low.
Greenhouse cucumbers should be planted in a soilless potting mix containing vermiculite and peat moss. Avoid the use of typical potting soil, which could introduce disease into the closed environment. Mixing in a dry organic material such as peanut hulls will help with drainage, but avoid fresh organic matter that can create nitrogen deficiency. Use a fertilizer that is formulated for cucumber plants.
The potting mix should be kept moist to avoid wilting, which can have a negative effect on the taste and quantity of greenhouse cucumbers. Avoid using cold water, which can slow the growth of these plants. Instead, use water with a temperature above 65 degrees F (18.3 degrees C).
Space greenhouse cucumbers adequately to avoid contact between mature plants. Typically, this requires about 20 inches (50.8 cm) between plants. It is best to allow adequate working space between rows. Once the greenhouse cucumbers have developed at least three pairs of leaves, they can be moved into individual containers or planted in beds. A trellis or other type of support will be necessary for these plants, as they can sometimes grow to more than 10 feet (3 m) in height.
Fruit can be harvested when it has achieved a consistent diameter throughout the length of each cucumber, which typically occurs between 12 and 15 days after the appearance of the flower. It is best to remove mature cucumbers before the blossom ends become yellowish. Expect to harvest cucumbers approximately every other day.
The European variety of cucumber is most commonly grown in greenhouse conditions, although there are also Japanese and American types available. Mature cucumbers of the European plants are typically dark green and approximately 12 inches (30.5 cm) in length, with a thin skin and mild flavor. These plants are high-yield because they tend to produce at least one cucumber from the base of each leaf.