Hydroponic Culture of Cucumbers
The most popular cucumbers grown hydroponically in greenhouses are the “European” or “Long English” cucumbers (photo 1). Other cucumbers becoming increasingly in demand are the Beit Alpha (BA), Japanese or Persian pickle cucumbers (photo 2). They are similar to the European cucumbers, but smaller in size, usually 4- to 6-inches in length compared to the European ones that average from 12- to 14-inches. These cucumbers are all seedless and “burpless” in nature with thin skins that do not require their peeling before serving in salads. Due to their thin skins, they lose moisture rapidly so must be shrink wrapped to prevent weight loss. European cucumbers are the second most important crop hydroponically in terms of acreage. Unlike tomato plants that are hardy, these cucumber plants are more delicate. They must be constantly trained to a special form (renewal umbrella) to obtain maximum yields. If left unattended they will quickly entangle in themselves and production will fall greatly. They cannot be easily pruned to get their correct form back as what can be done with tomatoes so correct training is necessary throughout their life cycle.
All cucumbers grown in greenhouses hydroponically are of varieties that can be trained vertically, unlike the regular field varieties that grow along the surface. The choice of variety depends on your environmental conditions and the presence of diseases. I have found for hot, humid conditions of Florida and Anguilla that it is imperative to select varieties that are highly tolerant or resistant to powdery mildew fungus. Some of these varieties include: “Dominica,” “Logica,” and “Marillo.” For indoor conditions it is possible to use other varieties such as, “Millagon,” “Discover,” “Corona,” “Accolade,” and “Crusade.” There are many more varieties that are probably suitable. Your choice will depend upon the results of various trials you can carry out under your conditions. For BA cucumbers I have found the following to be good for our conditions: “GVS 600,” “GVS 601,” (Golden Valley Seeds), “Nimmer,” (Nirit Seeds), “Darius,” and “Sarig,” (Hazera Seeds). If you are growing under conditions of high relative humidity (RH) be sure to use Powdery Mildew tolerant or resistant varieties. In your home you should be able to control humidity and temperatures close to optimum levels then these diseases will not be as prevalent.
Cucumbers like somewhat higher temperatures than tomatoes. Their minimum night temperatures should be about 68 F and during the day maximum temperatures of 75 to 78 F are ideal. Relative humidity should be maintained about 75%. Light levels of 5500 lux (510 foot candles) for 14 to 16 hours per day are adequate. Carbon dioxide enrichment from 800 to 1000 ppm will help the plants compensate for the lower than natural sunlight conditions when using artificial lights.
Similar to tomatoes, cucumbers are started in rockwool cubes 1 1/2” x 1 1/2” x 1 1/2” sowing one seed per cube. Be sure that the seed is placed deep into the hole of the cube so that it will not dry and at the same time that will help the seed coat to come off as it germinates. Be sure to sterilize any flats with a 10% bleach solution prior to placing the rockwool cubes in them. They should be sterilized a day before to be sure that all volatile chlorine is dissipated. Be sure to presoak the cubes well before sowing. Use raw water for the first 2 to 3 days until the cotyledons (seed leaves) fully expand. Thereafter, use a half-strength nutrient solution. At 4 to 5 days space the cubes in the trays to double spacing by breaking the cubes apart (photo 3). Do not lie them down on their sides as we do for tomatoes and peppers. Transplant the seedlings in the rockwool cubes to 3- or 4-inch rockwool blocks at 8 days from sowing (photo 4). Space the blocks in a checkerboard pattern to 6 per flat. Presoak the blocks well with water before transplanting. Hold the plants in the rockwool blocks for 7 to 10 more days before transplanting to the growing area of rockwool or perlite (photo 5).
If you are going to use rockwool slabs as the growing system, soak the slabs for a day, as was done for tomatoes, prior to transplanting so that there are no dry spots in the slabs. If you are going to use bato buckets or other containers of perlite, it is best to sterilize the substrate prior to transplanting. Soak the pots of perlite with a Zerotol solution of a dilution of 1:50 or 2.5 fl. oz. per U.S. gallon of water. Soak the substrate a few days before transplanting. Thoroughly drench the substrate several days before transplanting. Inoculate the substrate prior to transplanting with “PlantShield” (photo 6). PlantShield is a beneficial fungus, Trichoderma harzianum, strain T-22 that is applied to the medium just before transplanting. It is preventative control for diseases caused by Pythium, Fusarium, Rhizoctonia, Thielaviopsis and Cylindrocladium. Drench the pots of perlite at the rate of 1 to 2 tablespoons per 5 gallons of water. You will need about 1/3 to 1/2 gallon of this solution per bato bucket of perlite to thoroughly drench the medium.
Transplant one European cucumber per pot with two drip emitters per pot. Place one at the edge of the rockwool block and the other beside the plant (photo 7). If you wish to grow BA cucumbers transplant two plants per pot. Irrigate with one emitter at the corner of each block with the plant and place one emitter between the two plants. The irrigation cycles should be sufficient during the daylight period to permit at least 25% leachate (drainage) during any given cycle to keep the nutrient levels in the substrate stable. Immediately support the plants with string and plant clips. For more details on transplanting and the irrigation system, please refer to my book “Hydroponic Food Production,” available through my website.
Cucumbers require more space than tomatoes. The European cucumbers are spaced to occupy 10 square feet of area per plant (photo 8). The BA cucumbers need about 4 square feet per plant. The bato buckets are spaced at 6 feet between rows by 16 inches within rows. By transplanting one plant (European cucumbers) or two plants (BA cucumbers) per pot we get the correct area per plant.
European cucumbers are trained very differently from tomatoes. The conventional method is the “Renewal Umbrella” system. All of the fruit and side shoots are removed from the leaf axils up to the eighth leaf. Then, allow two fruit to form, then remove one, then permit the others to form. The plant is usually only capable of supporting 3 to 4 fruit at any given time. When more than that form, the others will abort. All suckers (photo 9) and tendrils (stringy growths at leaf axils) (photo 10) must be removed. When the top of the plant reaches the overhead support cable, cut it off after allowing two side shoots to form above the wire (umbrella form). No fruit should be allowed to set where the laterals will develop. Attach these side shoots over the wire with a plant clip and permit them to fall down along the side of the main stem of the plant. Keep on removing side shoots on these “laterals” with the exception of one healthy one at the top of the plant near the support wire. Pinch the lateral once it reaches 4 to 5 leaves. Cut it off close to the top of the wire where the next “replacement” shoot is growing after two side shoot start to grow. Continue this “renewal” process as the old ones are replaced with new ones. Remove all of the tendrils on the laterals.
With European and BA cucumbers we only need to use plant clips to support the plants every 3 to 4 feet. Wind the plants around the support string in a clockwise direction always so that you are consistent in winding. To make this easier to avoid breaking the plants it helps to pull the string down as you wind the plant around the string.
BA cucumbers are trained differently from European cucumbers. Remove side shoots, tendrils and flowers for the first 5 leaf axils to permit vigorous growth. Then, allow the fruit to form on the main stem, but cut back the side shoots to two leaves and continue taking off the tendrils. When the main growing point arrives to the support cable above, do not cut it off, just bend it over and let it come back down. The side shoots and tendrils are then permitted to grow without pruning.
You do not need to use Tomahooks with extra string for supporting the cucumber plants as they are not lowered. Simply tie the string directly to the overhead cable or hook. As lower leaves turn yellow you may cut them off close to the stem with a sharp knife or pruning shears, but no more than one leaf per week.
Please refer to my book “Hydroponic Food Production” for more details of training methods for cucumbers.
European and BA cucumbers are seedless, so should not be pollinated. They are 100% female plants so no male flowers are present to pollinate. You do not need to vibrate the flowers as you do for the tomatoes.
European cucumbers take approximately 2 months from seed to first fruit harvest. In commercial greenhouses the plants are carried for a period of 10 months, generally from January through November in northern latitudes. In more southern latitudes such as Florida and here in the Caribbean (Anguilla) we keep the crop for only 3 months giving us 4 crops per year. In fact, here in Anguilla we have found that the cucumbers take only 5 weeks from seeding to first harvest, so we will change the crops every 2 1/2 months. In your home I would recommend that you not carry the crop more than 3 months as it gets very difficult to train and production falls greatly with the plant age, especially under artificial lighting.
BA cucumbers are in all locations grown on a cropping cycle of 3 to 4 months. Harvesting generally begins within 5 to 6 weeks from sowing and production continues for 8 weeks thereafter. That will fit 3 to 4 crops per year. Start new seedlings about 2 weeks before removing the old plants to shorten the down time between crops.
When growing hydroponic crops in your house, you will be growing a number of different crops such as tomatoes, cucumbers and peppers, so it is better to use a general formulation rather than a specific one for that particular crop. Each crop has different optimum nutrient formulations, but that is mainly applicable to commercial operations where the yields are directly related to profitability of the greenhouse. In your home profitability is not a factor. You are not going to save money by growing your own vegetables in your house as you will consume more electricity and supplies than the potential return on your production. You must consider growing your own vegetables as a rewarding hobby that can relieve stress from your work, provide you with safe vegetables, and enjoyment of truly “backyard” flavor in your vegetables.
In the previous article, “Culture of Tomatoes,” I presented a general formulation for growing tomatoes and other crops. Below is a specific formulation for cucumbers. It is presented in Table 1 expressed in parts per million (ppm) of each element. You would have to calculate the amount of each fertilizer you require for your volume of tank. You can refer to my book “Hydroponic Food Production” to learn how to do these types of calculations.
Table 1. Cucumber Formulation
|Fertilizer Salt as Source
|Calcium (Ca-200 ppm)
|Nitrogen (N-140 ppm)
|Phosphorus (P-50 ppm)
|Potassium (K-350 ppm)
|Sulfur (S-150-250 ppm)
|Magnesium (Mg-50 ppm)
|Iron (Fe-3 ppm)
|Iron Chelate (FeDTPA)
|Manganese (Mn-0.8 ppm)
or: Manganese Chelate
|Copper (Cu-0.07 ppm)
|Zinc (Zn-0.1 ppm)
or: Zinc Chelate
|Boron (B-0.3 ppm)
|Molybdenum (Mo-0.03 ppm)
or: Ammonium Molybdate
Similar to the tomatoes, you should make up a concentrated stock solution for the micronutrients with the exception of iron as their weights for a normal strength solution would be too small to weigh accurately.
The optimum pH for cucumbers is between 5.5 and 6.0. This is lower than for the tomatoes. Monitor and record the levels each day using a pH meter or indicator paper. Adjust the pH as for tomatoes using an acid or base. Wear gloves and protective goggles and always add acid to water.
Optimum EC ranges from 2.2 to 2.7 mS. If growth is too vegetative (too many leaves and not a lot of fruit) you can increase the EC to shift the plants to a more generative stage. Permit the leachate to reach as high as 30%, but lower that if the plants are too vegetative. If the growth is too generative, lower the EC and increase the leachate. Lowering night temperatures will also stimulate generative growth.
Pests, Diseases & Other Problems;
Cucumbers, like tomatoes, are prone to numerous pests and diseases. The most severe diseases of cucumbers are gummy stem blight and powdery mildew. As mentioned earlier, it is important to choose resistant varieties, especially for powdery mildew. A number of mites are very damaging to cucumbers. These include two-spotted, red-spider mite, carmine mites and broad mites. Broad mites are extremely damaging to the plants because they cause the growing points of the plants to die. They are very difficult to see as they are almost translucent. We shall discuss pest and disease problems in a future article. Also, please refer to my book, “Hydroponic Food Production” for further descriptions, photos and drawings of these pests.
Cucumbers are a little more demanding in care than tomatoes, but they will yield highly under the correct environment and plant training. The training of European cucumbers is a little more precise than the tomatoes and mistakes can reduce production significantly. However, with experience and some good books on culture you will soon be able to grow productive plants (photo 11).