Cultivating Hydroponic Cucumbers
Cucumbers thrive in hydroponics and are one of the highest yielding plants commonly grown in greenhouses. Here is a guide to growing the best cucumbers you have ever tasted using the hydroponic method.
Cucumbers thrive in hydroponics due to their rapid growth rate and requirements for warmth, moisture and nutrients. They are one of the highest yielding plants commonly grown in greenhouses.
One of the most rewarding aspects of growing your own cucumbers is the freshness of the harvested product. Most cucumbers consumed these days are thin-skinned, have lost moisture from the fruit flesh and require over-wrapping in plastic and refrigeration for shipment and sale.
Eating your own cucumbers fresh from the vine gives a crisp and juicy succulence that is hard to beat and is often quite a pleasant surprise for first-time cucumber growers.
Cucumbers have undergone somewhat of a renaissance in recent years due largely to the work of plant breeders churning out a diverse range of new and improved fruit types. While the standard, outdoor-grown, thick-skinned American slicers have dominated the market for decades, the long, thin-skinned, seedless European cucumbers have become a popular hydroponic greenhouse crop.
Even more recently we’ve seen some exciting new additions to the cucumber range available in supermarkets and produce stores. These include the crisp and delicate “snack” or “cocktail” cucumbers that, at 3- to 4-in. long, are marketed as ideal for children’s lunchboxes.
Read also: What’s the Problem? Hydroponic Troubleshooting
There are also Lebanese cucumbers, which are mild and smooth-skinned, typically sold at 4- to 6-in. long. Then there are the white, rounded apple cucumbers; yellow lemon cucumbers; and the most recently released is the small, sweet Beit Alpha cucumbers.
Along with an impressive range of commercial hybrid cucumber types that offer improved yields and disease resistance, there are also a number of heirloom cucumber types available for the hobby grower, including those of Indian and Oriental heritage, in cultivation for more than 3,000 years.
Apart from eating them fresh, cucumber varieties that produce small (2- to 3-in. long), seedless, perfectly formed cucumbers can be used to create homemade pickles (gherkins) that are bottled in vinegar in a range of flavors if other hydroponically grown herbs and spices such as chilies, dill, basil, tarragon or garlic are included.
Two or three hydroponically grown gherkin plants are enough to provide a year-round supply of pickles, provided care is given to cultivar selection.
Gherkins, just as with many cucumbers, are susceptible to powdery mildew, a disease that can wreak havoc in an indoor garden. To prevent this, only mildew resistant gherkin cultivars should be selected as this means a lot less spraying and a longer, healthier crop.
There are many gherkin or pickling cucumber seeds to select from, including varieties of green and white-skinned types, but the main characteristics to consider with hydroponic crops are compact plant size, wide disease resistance and the bearing of parthenocarpic (seedless) fruits.
What are the Best Cucumber Varieties for Hydroponics?
Cultivar selection with cucumbers can be a little confusing. There are a number of cultivars within each cucumber type to select from and new varieties are released each season. When browsing seed catalogs, points to look for are those that make growing cucumbers just that little bit easier and result in the type of fruit you most want to eat or pickle.
Read also: The Kratky Method: A Simple and Fun Way to Grow
Cucumber types may be described as burpless, bitter-free, parthenocarpic, spineless and gynoecious, with a range of disease resistances listed, along with information on fruit size, shape, color and yields. Hybrid cucumber varieties are preferred for hydroponic production as many offer resistance to major diseases such as powdery mildew that are extremely common in types with no resistance and can be difficult to control long term.
Seedless cucumbers are termed parthenocarpic, meaning they set fruit without the need for pollination and hence no seeds form in the flesh. These are the preferred types for hydroponic production, although seeded American slicer types can also be grown under soilless cultivation.
Gynoecious means the plants produce female flowers only (although small numbers of unwanted male flowers can sometimes develop under certain environmental conditions). Gynoecious plants mean no pollen from male flowers will be present to pollinate the female plants, as that would result in seeds forming, which often creates misshapen fruit.
Gynoecious cucumber plants are also higher yielding, thus more productive than if seeded fruit was being grown.
Most modern cucumber cultivars used in hydroponics are relatively bitter free and burpless, although plant stress can result in the production of the compound cucurbitacin in the fruit, making them less palatable.
Older, heirloom and open-pollinated varieties of cucumbers often develop bitter flavors, particularly if the fruit is left too long on the vine before harvesting, and under conditions of moisture, temperature or pest and disease stress.
Ideal Growing Conditions for Cucumbers
Seeds of good hybrid cucumber varieties may cost as much as $1 each or more. Given the number of fruit a single healthy vine can produce, this investment is certainly worthwhile.
Because of seed cost, cucumbers are best sown into individual cells or blocks of rockwool, coir or other clean and sterile grow media. Germination occurs best at 80 to 82°F and is rapid, with root emergence seen within two days. Young seedlings are best hardened off gradually at 72 to 75°F before planting into a hydroponic system.
Cucumbers are typically vining plants and should be strung upwards for support to maximize the use of vertical space. However, there are some more compact bush types that can be grown in smaller containers where there is insufficient vertical room.
All cucumbers are moderate- to high-light crops that require warm temperatures (60 to 82°F) and can be grown alongside plants with similar requirements, such as tomatoes and peppers.
Read also: Dialing in Hydroponic Drip Irrigation
They can be grown two to three plants per planting space and trained upwards and along strings or wires. Moisture retentive grow media, such as coco fiber, is well-suited to growing cucumbers and several successive crops can be grown in the same substrate.
Nutrient solutions should begin on a standard vegetative formulation at a moderate EC of 1.8 to 2 and pH of 5.8. This should then be switched to a fruiting formulation with higher potassium levels for maintenance of good fruit quality as soon as the first tiny fruitlets have formed and maintained until the crop is finished.
Under hot growing conditions, the EC can be dropped back slightly, particularly if the plants are wilting under overhead lights. Cucumber vines are largely indeterminate so they need to be carefully trimmed and trained to prevent them from taking over the entire growing area.
Growth can be directed upwards to an overhead support and then downwards again so the maximum number of fruit can be obtained from a minimum of vertical space. Cucumbers benefit from CO2 enrichment that will increase yields and speed up crop growth.
Humidity levels around the cucumber plants are also important. High humidity not only promotes certain fungal diseases, but can also restrict the transport of calcium out to the leaf tips and developing fruit, resulting in tip burn and cell collapse.
Low humidity can favor other problems such as mite infestation and even wilting if large volumes of moisture are lost from the plant’s large leaf area faster than it can be replaced via root uptake.
Sufficient air movement within the indoor garden should be provided so cucumber plant foliage can be seen gently moving in the breeze. This not only assists with humidity control, but also brings fresh CO2 to the leaf surface for photosynthesis.
Pests, Diseases, and Fruiting Problems to Look Out For When Growing Cucumbers
Cucumbers sometimes have the reputation of being difficult to grow and this is often based on issues growers sometimes have with diseases and misshapen fruit, or more commonly crooking. Crooking is a physiological problem that causes cucumber fruit to develop a slight to pronounced bend, rather than the ideal long, straight shape.
Read also: 8 Crop Micronutrients Growers Can't Ignore
This disorder usually begins at an early stage of fruitlet development and remains until maturity. Crooking can have several causes, including a leaf or stem interfering with growth of the fruit, feeding damage by insects such as thrips, restrictions caused by training strings or wires and a number of cultural or environmental conditions, such as high or low temperatures, excessive watering, stagnation of the nutrient solution and imbalances of certain mineral elements.
The main insect pests of indoor hydroponic cucumber crops are mites, thrips, whiteflies and occasionally aphids, all of which need careful control as they not only reduce yields, but also affect fruit quality.
The most common disease in non-resistant cultivars is powdery mildew, which will completely kill back plants if not controlled. The best form of defense against this pathogen is resistant cultivars. Wilt diseases such as fusarium, verticilium, pythium and phythothera can occur, but are less common in hydroponics.
Cucumbers are one of the most rewarding hydroponic crops to grow. Fast-growing and high yielding, cucumbers are highly productive with some attention to training and pruning and a well-balanced nutrient solution. Consider growing cucumbers and you’ll soon be making great use of an indoor growing space.
Written by Lynette Morgan | Author, Partner at SUNTEC International Hydroponic Consultants
Dr. Lynette Morgan holds a B. Hort. Tech. degree and a PhD in hydroponic greenhouse production from Massey University, New Zealand. A partner with SUNTEC International Hydroponic Consultants, Lynette is involved in remote and on-site consultancy services for new and existing commercial greenhouse growers worldwide as well as research trials and product development for manufacturers of hydroponic products. Lynette has authored five hydroponic technical books and is working on her sixth.