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