Cucumbers are a tropical, vine-growing vegetable that thrives in consistent warmth and high humidity, making them perfectly suited for the controlled environment of a greenhouse. Cultivating them indoors provides protection from fluctuating outdoor temperatures and common pests, allowing for an extended or even year-round harvest. A greenhouse allows a grower to precisely manage the conditions necessary to maximize fruit quality and yield.
Selecting the Right Cucumber Varieties
The selection of a specific cucumber variety is the first step toward a successful greenhouse harvest. Since indoor environments make insect pollination unreliable, choosing parthenocarpic varieties is necessary. Parthenocarpic cucumbers set fruit without fertilization, meaning the fruit develops without pollen transfer, resulting in seedless or nearly seedless cucumbers. This method produces a higher yield and better quality fruit because it removes the need for manual pollination. Most modern greenhouse varieties, such as the long, smooth English cucumber, are naturally parthenocarpic.
Growers can choose between slicing types, which are generally long and smooth-skinned, and pickling types, which are smaller and sometimes have spines. Both types have been bred into excellent parthenocarpic varieties suitable for greenhouse use. Varieties with resistance to common diseases like powdery mildew are also preferable to ensure a continuous, healthy growing season.
Establishing Optimal Climate and Substrate
The primary advantage of a greenhouse is maintaining the consistent, warm environment cucumbers require. Daytime air temperatures should be maintained between 75°F and 85°F for vigorous growth and fruiting. Nighttime temperatures must not drop below 60°F to prevent chilling and ensure continuous plant metabolism.
High relative humidity is equally important, thriving when air moisture is between 70% and 80%. Methods like misting the air or using a fogging system help maintain this level. Proper air circulation is necessary, however, to prevent high humidity from creating conditions favorable for fungal diseases like powdery mildew.
The growing medium must be warm, well-draining, and rich in organic matter. Soilless options like perlite, rockwool, or coconut coir in grow bags allow for precise control over nutrient delivery and pH levels. The root zone temperature should be maintained above 70°F for the fastest establishment of young plants. Supplemental lighting may be necessary during winter or in northern latitudes to provide the 14 hours of intense light required for high yields.
Essential Ongoing Care and Plant Training
Consistent and deep watering is necessary to support the large leaves and rapid fruit development of greenhouse cucumbers. Drip irrigation systems are highly recommended because they deliver water directly to the root zone while keeping the foliage dry, which is a major defense against foliar diseases. Water requirements increase dramatically once fruiting begins, and any shortage can quickly lead to misshapen fruit.
Cucumbers are heavy feeders and require a continuous supply of nutrients, often delivered through the irrigation water in a process called fertigation. During the initial vegetative growth phase, a fertilizer higher in nitrogen supports the development of robust vines and leaves. As the plants transition into fruiting, the nutritional balance should shift to a more balanced formulation to support the production of flowers and fruit.
Plant training is mandatory to maximize light exposure and manage space. The vines must be trained vertically, typically using a trellis system or strong wires suspended from the greenhouse structure. The umbrella system is a common technique where the main stem grows to the top wire, and the growing point is then pinched out.
Pruning focuses on directing the plant’s energy toward fruit production and improving airflow. Lower lateral shoots should be removed from the first few feet of the main stem to prevent disease spread from the substrate. Side shoots that develop higher up can be allowed to produce one or two fruits before being removed beyond the developing fruit.
Pests like spider mites and whiteflies can thrive in the warmth of a greenhouse. Integrated pest management (IPM) strategies, including the introduction of beneficial insects as biological controls, are preferred over chemical treatments. Good sanitation and regular inspection of the undersides of leaves are necessary to catch infestations early.
Pollination and Harvesting
For the recommended parthenocarpic varieties, the female flowers will develop into fruit without any external intervention. If a standard non-parthenocarpic variety is being grown, manual pollination is required.
Manual pollination involves collecting pollen from the stamen of a male flower using a small brush or cotton swab. The male flowers, which appear on a thin stalk, are then used to gently dust the stigma, or center, of the female flower. Female flowers are easily identified by the miniature, immature cucumber swelling directly behind the petals.
Cucumbers grow quickly in the optimal greenhouse environment, and harvesting typically begins between 50 and 70 days after seeding. The fruit should be picked when it has reached the desired length, the color is uniform, and the skin is firm. Frequent picking is necessary to encourage the plant to produce more flowers and continue setting new fruit. Allowing cucumbers to become too large or yellow on the vine slows down overall production. The fruit should be cut from the vine with a sharp knife or shears, leaving a small piece of stem attached.