Cucumbers (Cucumis sativus) are an excellent vining crop for greenhouse production. They are prolific plants that produce mild and delicious fruits, and they can be a great alternative vining crop to tomatoes if a market for them is available. Armed with the information below that highlights some of the fundamental aspects of greenhouse hydroponic cucumber production, you might want to give cucumbers another look as a crop to grow in your greenhouse.
Choose the Right Variety
The variety of the cucumber is much of the appeal of greenhouse cucumbers, so genetics matter. Greenhouse cucumber fruits differ from their field counterparts in that they are seedless and have a thinner skin that doesn’t require peeling. It is important to select the right cultivars for greenhouse production, nothing other than the standard long or cocktail-sized, thin-skinned English or Dutch varieties or the slightly thicker-skinned beit alpha varieties.
Propagate With Close Attention to Detail
Greenhouse cucumber seeds have high germination rates. Unlike most hydroponic crops started in small seedling sizes, cucumber seed can be directly sown, individually, in 4-inch blocks of coconut coir, stone, or mineral wool, or any similarly suitable substrate for hydroponic production. Warm temperatures up to the low 80s for the first few days will improve speed and uniformity of germination. Fertilize seedlings with a moderate-strength nutrient solution during propagation. After plants have three or four mature leaves, they are ready for transplanting.
Once cucumber transplants are ready, they can be grown-out in systems used for other vining greenhouse crops such as Dutch buckets filled with perlite or slabs of stone wool or coconut coir in a gutter system. Plants are most commonly grown in double rows in the greenhouse with both systems.
Provide Lots of Light and Meet Cucumbers’ Need for Feed
Cucumbers grow best with warm temperatures and high light. Maintain air temperature between 75°F and 85°F during the day and about 10 degrees cooler, 65°F to 70°F, at night. Cooler night temperatures can slow down crops. Cucumbers are also a high-light plant and, aside from summer, they are usually under light-limited conditions. Plant productivity increases with supplemental lighting.
Like other vining, fruiting crops grown hydroponically, cucumbers are heavy feeders. While a more dilute nutrient solution is used during propagation, the nutrient solution during finishing should be maintained between 2 and 3 mS·cm–1. Once plants are fruiting, potassium concentrations in the fertilizer can be increased by up to 50% more than nitrogen concentrations.
Match Vine Training to the Method
As a vining crop, cucumbers require training throughout the crop cycle, though there are different methods that may be used. The simplest method is the drape method, whereby the vines are trained onto vine twine and, upon reaching the trellis wire, are trained over the wire and grow down. The V-cordon method is similar to traditional draping, but the trellis wire is pulled farther out from the stems, with stems growing up to the trellis wire at an angle into aisles. Growers use this method to maximize light interception for crops produced under low light. For the umbrella method, growers train cucumbers up to the trellis wire, and then they are pinched off and two stems are allowed to drape over the trellis wire and grow down. This method is similar to bifurcated tomato plants in that a single plant can ultimately support two fruiting stems.
To keep cucumber plants as productive as possible, they will need to be pruned as well. First, constantly remove the tendrils from the plants. If the tendrils are left to grow, they can become problematic in vine maintenance. Additionally, the fruits for most greenhouse cucumbers should be thinned to leave a single fruit developing at each leaf to maintain fruit quality. Only some of the small-fruiting cucumbers should be allowed to produce multiple fruits at each leaf.
Harvest Frequently to Ensure Good-Sized Fruits
Most standard cucumbers are harvested when they are 12 to 14 inches long. However, some smaller-fruited cultivars and some of the beit alpha types are harvested when fruits are from 4 to 8 inches long. Harvest fruits frequently to avoid excessive crop loads and promote normal fruit development.
While the thin skin of greenhouse cucumber cultivars is one reason for their popularity, the thin skin also makes postharvest quality maintenance more challenging. Shrink-wrap fruits to prevent moisture loss and maintain fruit turgidity. The traditional thin-skinned cultivars must be shrink-wrapped to maintain product quality. Alternatively, the slightly thicker-skinned beit alpha varieties do not require individual shrink-wrapping and can be packaged in bags, on clamshells, or on trays.
Be Proactive About Pests and Diseases
Powdery mildew can be one of the most problematic diseases in a cucumber greenhouse. In addition to watching humidity levels in the greenhouse, select varieties with resistance to this disease. Scout carefully to identify any aphids, whiteflies, or thrips on cucumbers.