B's Cucumber Pages


Greenhouse Cucumbers


From Greenhouse Tomatoes, Lettuce, and Cucumbers by Wittwer, S.H., and S. Honma. East Lansing: Michigan State University Press, 1979. Section 3, Greenhouse Cucumbers.


Amazing Information in this Document:

Introduction
Protected Structures
Varieties
Pest Control
Plant Growing
New Types of Culture
Straw Bale Culture
Peat Culture
Rock Wool Culture
Nutrient Film Technique
Grafting
Harvesting

Introduction

The production of greenhouse cucumbers in many parts of the world parallels that of greenhouse tomatoes. The cucumber is a semi-tropical vegetable, and grows best under conditions of high light, humidity, moisture, temperature, and fertilizer. Its growth habit, similar to the tomato, is indeterminate. It will produce fruit continuously where disease and insects are controlled. The cucumber, however, is more sensitive than the tomato to low temperatures, which can cause reductions in both growth and yield.

The cucumber is almost always grown in rotation with lettuce and tomatoes, or in rotation with bedding or vegetable plants. It is possible to grow cucumbers after greenhouses become empty in the spring following bedding plant production.

Growing of greenhouse cucumbers can be a profitable business for progressive growers. However, as with tomatoes and lettuce, it requires practical know-how and technical knowledge. The production of a quality product is an exact and expensive venture, involving high technology. Recent large scale ventures in the comparative production of greenhouse tomatoes and cucumbers suggest it is easier to successfully grow cucumbers than tomatoes. The fuel costs are, however, greater with cucumbers than tomatoes.

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Protected Structures

Greenhouse structures described for the growing of tomatoes and lettuce can be used for the growing of cucumbers, with a slight modification in heating systems. Cucumbers require a higher temperature for satisfactory growth. Sandy loam soils, high in organic matter, are preferable. The roots of the cucumber plant require good aeration. A system of drainage is essential, and the same drainage tiles can be used for steam sterilization. To maintain a loose friable soil, organic matter--such as rotted manure, chopped hay, peanut hulls--must be added once a year. Fresh organic materials should not be added to the soil, since they may cause nitrogen deficiency of the crop. The soil should be well fertilized and tilled, and ridges built prior to planting. Back to the Table of Contents...


Varieties

Prior to the introduction of European seedless cucumbers, the standard greenhouse varieties grown in North America were those developed for field production such as Burpee Hybrid, Highmoor, etc. These standard or North American varieties are 7-10 inches long, of fairly uniform width throughout the length, thick-skinned, and dark green with light green mottled stripes. The flowers of these varieties must be pollinated by bees to set fruits. The fruits, therefore, contain well developed seeds when picked for market, and are indistinguishable from field grown types. Very few, if any, of these cucumbers are now grown in the United States or Europe.

The long seedless European cucumber has, in recent years, replaced the North American varieties. Plantings are found in Canada, California, Arizona, and Ohio. It is a product that originated from European greenhouses. The fruits of the European types are seedless, 12-20 inches long, have a slightly wrinkled surface, slightly ridged lengthwise, uniformly green, non-bitter, thin skinned, and usually have a short neck on the stem end. No peeling is required before eating. The thin skinned fruit is either waxed or shrink- wrapped to prevent excessive moisture loss. The cucumber is parthenocarpic and sets fruit without pollination. Pollination in these types should be avoided, since it causes seed development, and the fruit becomes clubbed at the blossom end and develops a bitter taste.

There are three types of the European seedless cucumber. They are subdivided by the flowering habit: (1) the all female, which produces only female or pistillate flowers; (2) the gynoecious, which is predominantly female with some male or staminate flowers appearing; (3) the monecious, which has both male and female flowers. All of these three types produceee fruit parthenocarpically, but the monoecious and predominantly female can produce seeds and, therefore, bees must be kept out of the greenhouses or the male flowers should be removed as soon as they become visible and prior to opening. The monecious types, which continuously produce male or staminate flowers, are not recommended. Predominantly female types can be used with confidence. The few male flowers that develop, however, should be removed. The all female type is recommended, since they produce no male flowers.

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Pest Control

European types of cucumbers have shown little resistance to diseases. Some of the varieties have resistance to scab (Cladosporium cucumerinium) and to leaf spot (Cercospora melonis). Varieties resistant to powdery mildew are being developed. They are also subject to the same insect problems as the standard American seeded types. Both red spider mites and white fly can be controlled biologically by appropriate use of parasites and natural predators as described for tomatoes.

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Plant Growing

Cucumber plants are grown in peat pots, soil or peat blocks, Kys-Kubes or BR-8 block, or in clay or plastic pots. The soil or soil mix used for the pots should be properly sterilized before seeding, and the seed treated with a fungicide to prevent damping-off. One or more seeds are placed in the pot and, when the plants are properly established, are pinched to one plant per pot. Temperature during germination should be near 80F (28C) and after germination at 70F (21C). Plants should be grown rapidly, with no check in growth. Additional fertilizer may be needed toward the end of the growing period. Nitrogen, at a rate of 1 l/4 lbs. of ammonium nitrate in 1 gallon of water and diluted to 1:200, should be fed to the seedlings.

Light. For early spring crops, supplemental light for the young seedlings is desirable. Cucumbers, in the early seedling stage, respond to supplemental light. Day length should be extended to 12-14 hours with 1,800-2,000 foot candles at the plant level. Plants should be progressively spaced as they grow to avoid crowding and becoming spindly. Leaves of adjacent plants should not touch. For the spring crop, approximately a 5 week growing period from seeding (mid-winter) is required; and for the fall crop, a 4 week period (mid-summer) is needed prior to transplanting.

Temperature Requirements. Plant growing temperatures between 80 to 85F with plenty of sunlight are ideal for good growth. Minimum temperatures should not be lower than 70F during the day or night. In the fall, some heat must be provided if the outside temperature falls below 60F.

Planting and Spacing. Plants are placed in permanent beds at the 4-5 leaf stage, or before they become pot bound. Approximately four square feet per plant are required for the North American varieties. Generally, two rows are spaced 30 inches apart, and then an alley of 40 inches provided between the pair of rows to allow for working space. Plants in the row are spaced 16-18 inches apart. For the European types, 7-9 square feet per plant for the spring crop, and 9-10 square feet per plant for the fall crop are desired. The increased space for fall grown crops will compensate for the shorter daylength and less intense sunlight. A minimum of 5 feet between rows, and a 20 inch spacing within the row is advised.

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Carbon Dioxide Enrichment. Enrichment of the greenhouse atmosphere with carbon dioxide up to 1500 ppm both in the seedling and permanent growing area will increase growth and yield by 25 to 50 percent. In the winter, carbon dioxide is introduced beginning with sunrise and continued until one to two hours before sunset. In the spring and early fall with the need for ventilation, the enrichment period is shortened, since the carbon dioxide escapes through the opened vents. All details of carbon dioxide enrichment outlined for tomatoes and lettuce apply to cucumbers.

Mulching. Mulching is suggested for cucumbers. Straw, hay, peanut hulls, or corncobs are placed in the alternate or wide rows. The mulch reduces soil water evaporation, soil compaction, and soil temperature fluctuations. The decaying organic matter also liberates carbon dioxide, which promotes increased growth.

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Training and Trimming. The plants are trained upwards so that the main stem is allowed to climb to the overhead wire along a polyethylene twine. Wires are attached 6 to 7 feet above the ground. The use of the V- cordon system is advised to make use of available light in the greenhouse. Two top wires are spaced 2 l/2 to 3 feet apart above the single row of plants. The twine for each plant is alternately tied to the overhead wires. This will incline the plants away from the row on each side, thus creating a better light receiving system.

The main stem is pruned to one leaf above the overhead wire, and the plant is tied below the leaf to the wire to prevent it from sliding down the twine. No fruit is allowed to develop on the main stem up to 4l/2 feet. All laterals are removed that appear for the first 2 feet. For the next 2 feet, the laterals are allowed to produce one leaf and then the growing tip pruned. In the third 2 feet, laterals are allowed to produce 2 leaves and are stopped. The two top laterals are trained over the wire in a canopy fashion or umbrella method and hung alongside the main stem to about l/2 or 2/3 of the way down. On these, the developing laterals are stopped after 2 leaves. T his method of training is somewhat more complex than the much simpler system now recommended.

Pruning of each plant is based on plant vigor and fruit load. Extensive leaf growth is prevented to allow proper coloring of the fruits. The development of the fruit is dependent on the continuing production of leaf axils. If too many fruits are set at once, fruit thinning is necessary to avoid malformed and non-marketable small fruit. Such fruit, as they appear, should be removed. Multiple fruits on an axil should be thinned to one. Weak unproductive laterals should be removed.

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Fertilizer Schedule. Similar to the greenhouse tomato, the cucumber requires a proper balance of nutrients to produce a good crop. It has a high fertilizer requirement; therefore, constant high levels of nutrients are required. Where organic matter is lacking, 50-70 tons per acre of well rotted manure should be worked into the soil prior to sterilization. If the soil is low in phosphorus and potash, 1,000 to 2,000 pounds per acre of 0-20-20 should be added after sterilization, and rototilled into the soil prior to planting. After the plants are set in the ground, the plants are watered with a starter solution (10-52-17), equivalent to l/2 to one ounce per gallon of water.

Where soil and tissue tests show a shortage of magnesium, or plant symptoms from a previous crop indicate a deficiency, incorporate 200-250 pounds of magnesium sulfate into the soil prior to planting. If magnesium deficiency should appear on the crop, the plants should be either sprayed with 5 pounds magnesium sulfate in 100 gallons of water, or 80 pounds of magnesium sulfate applied per acre in a water solution to the soil. Repeat the application, as needed.

Watering. Cucumbers have a high water requirement. Periodically, heavy watering is desirable to ensure proper penetration to the root zone. Warm water (not below 65F) should be used in irrigating. Cold water chills the roots, and will slow plant growth with a direct reduction in yield. During the warm spring and early summer, the leaves of cucumber plants should be sprinkled lightly to increase the humidity of the greenhouse and reduce water loss from the plant. This practice should be limited to the early part of the day, and should be terminated in time so that the leaves dry by nightfall. This will promote good growth and, at the same time, reduce incidence of mildew, Botrytis, and other leaf and stem diseases.

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New Types of Culture

Greenhouse cucumbers, in addition to being grown in regular greenhouse soils, may be produced on straw bales, in peat modules, troughs and bolsters, on rock wool, with artificial mixes, the nutrient film technique (NFT), Hygro-Flower systems, and sand culture. In each of these methods of culture, a slight modification from the nutrient requirements of the tomato is necessary.

Straw Bale Culture. This method of culture has been found more desirable for cucumbers than for tomatoes. Straw bale culture was first developed and practiced for successful greenhouse cucumber production in western Europe. One of the advantages is the release of carbon dioxide from the decaying straw. Straw bale culture can also be used where greenhouse soils are chemically contaminated. The decaying straw also provides a higher root temperature. Straw free from slow decomposing herbicides should be used. Even the slightest residue is sufficient to kill the cucumber plant after transplanting.

Details of culture are as follows. Wheat straw bales are placed end to end in 3-6 inch trenches, or flat on the ground on polyethylene film that is a foot wider than the bales. The bales are soaked with water before fertilizers are applied. The amount of water applied per bale depends on the condition of the straw, whether new or weathered. The average is 15 gallons per bale. Following three to four days of daily watering, 5-6 ounces of ammonium nitrate is applied per 40 lb. bale. This is followed by several days of daily watering. On the 7th and the 10th days, an additional 3 ounces of ammonium nitrate is applied. The bales are watered daily. Superphosphate and potassium nitrate at 10 ounces each are applied along with magnesium sulfate at 3 ounces, and 2 ounces of ferrous sulfate per bale on the 10th day. Water is applied daily to the bale until the plants are ready to set. The temperature of the bales may internally rise to 120 to 140F. Planting should not begin until temperature drops below 100F. If phosphate and potash are omitted during the fermentation process, these nutrients must be supplied to the plants soon after transplanting as a liquid feed.

Prior to planting the cucumber plant, a small bed of soil (top cap) is placed on the bale deep enough to take the ball of roots of the transplant. The top cap is made up of equal parts of sterilized loam and peat, and 1-2 pounds of ground limestone per bale. In Western Europe, white polyethylene is placed over the straw bales, and a hole is made over the soil cap for the transplant. The transplants are supplied liquid fertilizer through drip hoses. For the first three weeks, 5 ounces of ammonium nitrate in one gallon of water diluted to 1:200 is applied three times a week. From the third to the sixth week, 12 ounces of ammonium nitrate in one gallon of water and diluted to 1:200 is applied at every watering. From the 7th week to the end of crop, 8 ounces of ammonium nitrate, 2 ounces of potassium nitrate, and 2 ounces of magnesium sulfate per gallon of water diluted to 1:200 is applied three times a week.

For plants trained to the cordon system of culture, it is especially important for plants grown on straw bales to keep the twine slack enough to prevent the roots from being pulled from the soil, as the bales deteriorate and sink as the season progresses.

A modified straw bale culture for the growing of cucumbers is being used by the West of Scotland Agricultural College. This system requires a continuous liquid feeding, and removes the use of solid fertilizer and the need for an initial straw breakdown period. Straw bales on polyethylene are watered with a 2:1:2 liquid feed diluted to a conductivity factor (CF) of 16 (1.6 mmhos). Frequent small feeding of the liquid is made to the bales for a period of 10 to 14 days until the bales are well soaked. The bales are then top capped 5-6 inches deep, and transplants placed in them.

The liquid feeding begins 2 weeks later with the same fertilizer solution diluted to a CF of 8 (0.8 mmhos). Four to five weeks after transplanting, the concentration of the solution should be increased to CF of 16 and continued to the end of the crop. Back to the Table of Contents...


Peat Culture.

The technique for growing cucumbers in straw bale culture parallels that for peat substrates, such as beds or bolsters. There is a difference in nutrient requirement. Cucumber plants in peat cultures require more nitrogen and supplementary applications of lime, potash, and phosphate 4-5 weeks after transplanting. It is not easy to overcome the problem of lowering the potash and phosphorus levels by adding more to the base fertilizer for peat. Cucumbers are very sensitive to high salts. An excess will result in root damage.

Cucumbers grown in a peat substrate require large amounts of nitrogen in the early stages of growth to obtain the rapid growth desired. When heavy fruiting begins, high amounts of nitrogen and potassium are required with only a moderate amount of phosphorus. Growers are reluctant to add phosphorus because of possible blockage of the drip nozzles If the phosphorus is fed separately, and the lines washed, the plugging will be lessened.

It is recommended that 300 ppm of nitrogen and potassium be applied in the irrigation water for the first four weeks, then increased to 375 ppm from the 5th to 12th week, and dropped to 300 ppm until the end of the crop. Beginning the 5th week, 100 ppm of phosphorus should be added in a ratio of 1 part of phosphorus to 4 parts of nitrogen and potassium. This will prevent a deficiency of phosphorus.

Cucumber seedlings planted in peat, whether in bags or troughs, should be started dry and gradually wetted. It is important to avoid over wetting the peat before or soon after planting. This can result in chilling the plants, or cause them to stand in free water.

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Rock Wool Culture.

There is an increasing use of rock wool marketed as "Grodan" in growing greenhouse cucumbers in western Europe. Plants are started in 1 1/2 inch rock wool blocks with a small hole on the top. The cucumber seed is placed in the hole, and granulated rock wool is used to cover the seed to prevent washing out. The blocks are placed on a slightly sloping surface covered with plastic sheeting. A basic nutrient solution of 2 percent nitrogen, 11 percent phosphate, 40 percent potassium, 5 percent magnesium oxide and trace elements is required. The blocks are soaked with a solution containing 1.9 grams of the basic solution and 1.9 grams of nitrate limestone (calcium nitrate) in one gallon of water. As the seeds germinate, 9.85 grams of the basic solution and 3.42 grams of the nitrate limestone are dissolved in a gallon of water and are applied to the blocks.

As the plants begin to grow, the blocks are spaced so that the leaves do not touch each other. To prevent over watering and the possibility of slowing down the growth, the wetness of the blocks must be checked frequently. Pythium infection can be avoided by maintaining temperatures above 68F by using bottom heat and warm water for irrigation.

The plants are placed in the middle of rock wool slabs at the 3 to 5 leaf stage, and a drip nozzle accommodates each plant block. The slabs or mats are laid end to end on polyethylene sheets that are a foot wider than the blocks. The polyethylene is wrapped around the side and the top.

It is necessary to sample the nutrient levels in the rock wool mats several times a week, and to monitor the conductivity value of the solution. A concentration of 1.7-2.0 mmhos should be maintained. Irrigate 1-4 times a day. Irrigation should be terminated when dripping from the mats starts. Occasionally, some leaching should occur to avoid accumulation of excess soluble salts in the rock wool.

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Nutrient Film Technique (NFT).

This new method, along with the Hygro-Flo system of hydroponic culture, has the same advantages and limitations for growing greenhouse cucumbers as for tomatoes or lettuce. Developments at the Glasshouse Crops Research Institute at Littlehampton in the United Kingdom with cucumbers have paralleled those of tomatoes. Nutrient formulations similar to those outlined earlier for lettuce and tomatoes are satisfactory. Heating the water to raise the root temperatures may prove beneficial. The design specifications outlined for greenhouse tomatoes can be followed.

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Grafting.

Where root diseases such as Fusarium and Corkyroot are present in the soil, cucumber seedlings of the desired variety and type may be grafted onto resistant rootstocks such as Cucurbita ficifolia. The practice is common in Japan and western Europe. Seeds of C. ficifolia are normally planted 5 to 6 days later than the desired cucumber variety. Seeds of the rootstock should be pregerminated and transplanted into seedling boxes or flats. If there is difficulty in germinating seeds of the rootstock because of a hard seed coat, a small part of the side of the seed should be cut with a razor blade. This allows for the absorption of water. A loose friable soil containing peat and sand is desirable for growing plants of both the scion and the rootstock, since the plants are lifted and transplanted after grafting. Ten to twelve days after germination, the plants of the rootstock are ready to be grafted.

The approach graft has proven successful. Rootstock plants are carefully removed from the seedling flat, and a one-half inch downward incision is made with a razor blade below the first secondary leaf. The scion cucumber plant is carefully lifted, and an upward incision is made approximately at the same height of the incision of the rootstock. The lips of the incision are placed into each other and secured with a strip of adhesive tape. Both plants are then potted together and placed in a high humidity chamber or room for 10-12 days. All but one of the leaves of the rootstock are removed as soon as possible after grafting. The top of the rootstock above the graft and stem of the scion plant below the graft are cut after 10 days.

Grafted plants are earlier, root disease resistant, and produce a larger crop than non-grafted plants. They can also withstand lower soil temperatures. The disadvantages of grafting are the extra labor requirements. Virus diseases are also easily transmitted if a few plants are infected.

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Harvesting.

Fruits are harvested when they are more or less cylindrical and well filled. For the North American types, fruit should be 8-9 inches long, and 2-2 1/4 inches in diameter. For the European types, cylindrical fruits greater than 11 inches in length should be harvested. European seedless cucumbers, with their thin skins, lose moisture more rapidly than the North American types, and should be shrink-wrapped and stored in a cooler (50-55F) to retain high quality.

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Last Modified: August 28, 1997