Cucumbers grown hydroponically are a fast-growing, high-yielding crop that needs warm temperatures and lots of light. There is a range of different cucumber types in production. These include snack or cocktail ‘mini’ cucumbers with fruit harvested at 75–100 mm, these are spineless, seedless and several fruits are produced at each node; and the ‘Beit-Alpha’ types which produce 125–150 mm long, seedless fruits (Fig. 1.1). Both the standard European and mini cucumber cultivars are parthenocarpic and set fruit without pollination. Cucumber varieties should be selected which have genetic resistances to powdery mildew, leaf mold and cucumber mosaic virus as well as suitable fruit size and quality characteristics.
Cucumber propagation and production
Seed germinates rapidly, within 2–3 days, at 29°C in free-draining, sterile propagation media and young plants are ready for establishment into the hydroponic system within 2 weeks. Commonly used propagation materials include rockwool cubes, foam blocks, soilless peat or coconut fibre, and perlite substrates in small pots. Once seed has geminated temperatures are lowered to 25–26°C and a diluted, balanced vegetative nutrient solution applied. Once seedlings have developed three
or four true leaves, they are transplanted into the production system, and at this stage roots should be seen appearing from the base of the seedling container or cube.
Environmental Conditions For Cucumber Cultivation
Cucumbers are well suited to warm climates and grow rapidly if provided with sufficient water and nutrients. Drip-irrigated substrate systems are commonly used for production with plants grown in single rows at 30 cm spacing (Fig 2.1). A wide range of substrates may be used for hydroponic cucumber crops including rockwool, perlite, sawdust, peat, bark, coconut fibre and organic mixes. Gutter systems, slabs, bags, Dutch buckets and bed systems have all been used successfully for cucumber production. Because of the large and extensive nature of the root system and extremely high demand for oxygen under warm growing conditions mean that continuous aeration of the nutrient solution is required to maintain a healthy root zone.
Cucumbers require warm conditions, with air temperatures in the range of 24– 30°C and with a minimum night temperature of 18°C. High light levels are required for good yields and supplementary lighting is beneficial in low-light winter climates.
CO2 enrichment is also highly beneficial for cucumber crops up to a level of 1000 ppm. Studies have found that root cooling of hydroponic cucumber crops to 22– 25°C as compared with an ambient root-zone temperature of 33°C increased productivity by 71.4 to 74.3% in a recirculating hydroponic system.
Cucumber Training and Support Systems
The main training method used for greenhouse cucumbers is the ‘umbrella’ or cordon system. The upper portion of the
main stem is then permitted to set fruit in every second axil. When stem growth reaches the top wire, the plants are ‘stopped’ by removal of the growing point and two sides shoots are permitted to form and continue growth over the wire and back towards the ground. As much fruit as the plant can maintain is permitted to develop on the side shoots (Fig3.1).
A second common method of greenhouse cucumber training is the ‘V-cordon’ where single rows are spaced at 1.3 m with an in row spacing of 30 cm. Two overhead wires are spaced approximately 70–80 cm apart from each other and plants are trained up strings which are alternately tied to each wire. Fruit are pruned in the same way as in the umbrella system with all lateral branches removed as they appear on the main stem until this reaches the over head wire.
Crop Nutrition for Cucumber
EC levels of 2.2–2.5 mS/cm and pH of 5.6 – 6.0 are commonly applied and the crop also has a high transpirational water demand under optimal growing conditions. cucumbers require adjustment of the nitrogen to potassium ratio as the plant moves from vegetative to fruiting phases. An N:K ratio of 1:1.5 is suitable for fruiting, however, growers often monitor nitrogen and potassium levels in the nutrient solution leachate draining from the growing system and adjust this ratio based on analysis data and fruit loading levels.
Cucumber Harvesting and Yields
Cucumbers are a shorter-term crop than tomatoes or capsicums and are usually harvested for a period of 12–14 weeks before crop replacement. Harvesting should be carried out every 2–3 days. During harvest, fruits are cut from the vine and carefully handled to avoid bruising or damage as these are the main factors which reduce shelf-life. . All cucumber types are at risk of moisture loss postharvest which results in a loss of texture and turgidity; optimum storage temperatures are between 10 and 15°C with 80–90% humidity. Refrigeration should be avoided as this can induce chilling injury which reduces shelf-life.
Average yields of hydroponic greenhouse cucumbers are in the range 50–65 kg/m2 per year but vary depending on cropping schedule, climate, variety grown and level of technology.
Cucumber pests & diseases
Cucumber crops are prone to similar pests and diseases as many other fruiting crops. These include greenhouse whitefly (T. vaporariorum), tobacco whitefly (B. tabaci), greenhouse thrips (Heliothrips haemorrhoidalis), two-spotted mite (T. urticae), aphids and caterpillar larvae. Mite damage symptoms include mottled, chlorotic leaves resulting from mite feeding damage, followed by the development of fine webbing and this is often initially misdiagnosed as nutrient deficiency or toxicity damage. Common diseases include powdery mildew and viruses, including cucumber mosaic virus which is transmitted largely by the feeding of aphids, with control and prevention of entry of these pests being important steps for virus control
Source: Hydroponics and Protected Cultivation, A Practical guide By Lynette Morgan