Greenhouse Cucumber Production

Hunter Johnson, Jr., Extension Vegetable Specialist, Univ. Of CA

Gary W. Hickman, Farm Advisor, San Joaquin County

Three distinct types of salad cucumbers are grown in greenhouses: the standard American slicer, the Japanese, and the European greenhouse.  Information in this publication refers mainly to the European greenhouse type, as it is most widely grown.  Cultural requirements for the other two types, however, are similar.  Fruits usually weigh about 1 pound and are 12 to 14 inches long.  These dark green, seedless cucumbers are mild in flavor and have a thin, tender skin that does not require peeling.


 

Flowering Habit and Fruit Set

All European greenhouse varieties grown in the United States produce fruit without pollination.  They are gynoecious in flowering habit, (i.e. they produce only female flowers; Figure 1) and fruits develop without the need for pollination by bees or any assistance by the grower.  One or more flowers are produced at the base of every leaf; thus, yield potential is high.  Gynoecious greenhouse cucumber varieties differ in their degree of femaleness, which is both genetically and environmentally controlled, but those designated as žall femaleÓ rarely, if ever, produce male flowers.  Under conditions of poor light and low temperatures, some gynoecious varieties will produce male flowers.  If pollen is transferred from male to female flowers, seeds will develop, distorting fruit shape and making them unmarketable.  For this reason, it is important to exclude bees to avoid pollen transfer or to prevent them from carrying pollen from outside garden plantings into the greenhouse.


 

Varieties

Most of the varieties grown in greenhouses are F1 hybrids produced by seed companies based in Holland.  They vary somewhat in vigor, disease resistance, fruit size, and other fruit characteristics, such as color, ribbiness, neck length, and spininess.  Many tested varieties produce good yields and fruit quality, but most growers tend to favor Sandra or Toska 70.  Two other frequently used varieties are Farbio and Corona.  All of these hybrids have resistance to diseases, which are important in European greenhouses, such as gummosis (Cladasporium curcumerisum), leaf spot (Corynespora melonis), and downy mildew (Pseudoperonospora cubensis) but they lack resistance to powdery mildew (Sphaerotheca fuliginea) and to viruses such as cucumber mosaic and watermelon mosaic, which are prevalent on weed hosts or in field plantings throughout the state.  Excellent resistance to powdery mildew is available in several hybrids such as Vetomil, Silvia, Bella, and Fidelio.


 

Cultural Practices

Greenhouse cucumbers grow rapidly under optimum environmental conditions, and fruit production begins 60 to 70 days after seeding.  For good production, a temperature range of 75 degrees to 80 degrees F during the day is desirable.  While peak daytime temperatures of 85 degrees to 95 degrees F are tolerable, prolonged periods of high temperatures may adversely affect fruit quality.  Night temperatures no lower than 65 degrees F will allow a rapid growth rate and earliest fruit production.  At 55 degrees to 60 degrees F, savings in fuel costs will be significant, but growth rate will be slower and harvest will be delayed.

Good soils for greenhouse cucumbers should be well drained, at least 48 inches deep, low in soluble salts, and free of soil-borne diseases.  Sandy loam is preferred to sand or clay.  If the greenhouse soil does not meet these criteria, several types of soilless growing systems can be used successfully.  These include various kinds of hydroponics, peat-lite (a mixture of sphagnum peat and vermiculite or perlite), and sawmill waste (mixtures of bark and wood chips and sawdust).  Hydroponic systems are capable of growing good crops of greenhouse cucumbers, but they are more costly to install and manage than other systems, and provide no special advantages in yield or fruit quality over soil culture.


 

Bag Culture

This system is very successful and preferred by many growers over soil.  The bag culture system consists of filling 4 mil. Black polyethylene bags of 5-gallon volume with ½ to 3/4 cubic foot of growing medium.  The bags are pre-punched with drain holes.  The principal growing medium in use has been sawmill waste of various types: bark, bark and rice hull mixtures, etc.  Composted and leached material is preferred over fresh because possible soluble substances may be toxic to plants.  Several successive crops can be grown, with no adverse effects on yield or quality, in sawmill waste medium which has been leached between crops to remove soluble salts.

One cucumber plant is placed in each bag, with bags spaced 16 to 18 inches apart in the row.  A complete nutrient solution is fed through a plastic spray stake in each bag, at a flow rate of about 0.1 GPM.  Nutrient solution is applied several times a day, depending upon temperature and plant size in the range of 1 to 4 quarts per day per plant.  The nutrient solution is usually provided from liquid concentrates diluted through a fertilizer proportioner.


 

Planting and Plant Growing

Plantings of greenhouse cucumbers are ordinarily started from transplants, but direct-seeding in greenhouse beds may also be practical for late summer or early fall plantings, when the time from seeding to fruiting may not be as critical and prevailing temperatures are warm enough for good seed germination without having to heat the greenhouse.  Midwinter direct-seeding is not recommended because it delays fruit production by 3 to 4 weeks and requires more fuel to produce plants in the fruiting stage than if plants were started in a nursery house.

Transplanting makes more efficient use of greenhouse space, because seed germination and early growth of plants can be confined to a smaller nursery area.  Disadvantages to transplanting are the costs of containers and the labor costs of transplanting.

Transplants should be grown in structures separate from those used for fruit production.  This allows temperature control to be confined to a smaller area and will be more conducive to good sanitation practices to ensure disease-free plants.  The nursery should be equipped with waste-high benches, environmental control equipment, and the necessary irrigation-feeding equipment.  Temperature should be maintained at a constant 85 degrees F (night and day) to accelerate germination.  Supplemental lighting to provide 16 hours of light per day will minimize the time from seeding to the three-leaf stage for transplanting.

The many types of plant growing containers available vary in cost and construction material, but all are capable of growing good plants.  There are two general types: (1) pots, plant bands, or nursery flats that must be filled with a soil mix and (2) solid containers made of pressed peat, soil or fibrous material.  Some types of pots are reusable many times after cleaning and sterilization; others are intended for only a single planting.  All solid containers are for single use, because they are planted with the plant to avoid disturbing the root system.

Several factors must be considered in choosing a container.  Labor is required to fill pots and new soil mix is required for every planting.  The additional cost of reusable pots is justified only if they are to be reused many times and the costs of filling, cleaning, and sterilizing can be minimized by mechanization.  Solid containers require no filling labor and are about equal in cost to reusable pots.  Use of solid containers minimizes nursery labor and storage space requirements and eliminates the need for equipment to fill and clean them.  Growing plants in solid containers also requires less greenhouse space.

Soil mixes for container-grown plants are usually either sand-peat mixtures or mixtures of sphagnum peat and either vermiculite or perlite. Peat-vermiculite or peat-perlite mixes are more costly than sand-peat mixes, but have the advantages of lighter weight and greater water--and nutrient-holding capacities.

Good cucumber plants can be grown in 3 to 4 inch pots or in 2 to 2 ½ inch solid containers.  Solid containers should be placed edge-to-edge in a standard nursery flat for growing purposes.  After seeding, any spaces left between adjacent containers can be filled with vermiculite to prevent container walls from drying between irrigations.  Plants grow to the three to four leaf stage and are ready for transplanting into the greenhouse in 2 to 3 weeks, depending upon temperatures and light conditions.

 Cucumber seed is expensive, but germination is close to 100 percent.  For this reason, it is practical and expedient to plant one seed per container.  The seed should be planted about ½ inch deep.  Irrigate the containers thoroughly after seeding, and then cover them with a sheet of clear polyethylene to prevent moisture loss and maintain more uniform soil temperature.  Cucumber seed germinates rapidly under warm temperatures (85 degrees F), and emergence will occur in 2 to 3 days.  Remove the polyethylene sheet as soon as emergence begins.

Cucumber transplants should never be allowed to become stressed for water or nutrients.  It is recommended that a complete nutrient solution (such as half-strength Hoaglands solution) be applied whenever irrigation is required.


 

Additional Pointers for Growing Good Transplants

  1. Be sure that the growing medium is free of plant disease organisms.  Store all containers  and soil mix material where contamination can be avoided.
  2. Sterilize all plant-growing containers between uses.
  3. Keep hose nozzles off  the floor, as the floor may carry disease organisms.
  4. If containers are used, fill to a uniform depth, making certain that the soil surface is  reasonably level.  Fill pots to ½ to 3/4 inch from upper edge to leave room for water  during irrigations.
  5. When irrigating (water or nutrient solution), apply enough to thoroughly wet the full  depth of soil.  This will ensure moist soil throughout the container and avoid salt buildup.
  6. 6. Cover seeded containers with clear polyethylene film until emergence to improve soil  temperature and moisture conditions.
 

Spacing, Training, and Pruning

The decision on the number of plants to be grown in a given area of greenhouse should be based upon expected light conditions during growth of the crop and also upon the method of pruning the plants.  When full sunlight is expected almost every day--as from mid-spring through late fall--more plants can be accommodated than they can under winterŪs low light.  With good sunlight, each plant is allotted about 5 square feet space.  Nearly twice that much space may be needed with low light to avoid leaf overlapping and shading by adjacent plants.  Also, more plants can be accommodated with the žumbrellaÓ system of training than on a system that allows many lateral branches to develop.  Almost all plants in the southwest U.S. utilize the žumbrellaÓ system because of its higher plant density and lower labor requirement.  (See Figure 1.)  With this system, growers plant 8,000 to 8,500 plants per acre.

Spacing between rows and plants within the row can vary with grower preference.  Rows are often spaced 4 to 5 feet apart, with plants 12 to 18 inches apart in the row.  With 12-inch row spacing, alternate plants are trained in opposite directions to form a V-cordon.  Wider spacing is used for vertically trained plants.

Cucumber plants are supported by strings suspended from a horizontal wire.  The wire is attached to the top of the wall at each end of the       house, so that it is located 7 to 8 feet above the plant  rows.  Heavy sisal or polyethylene twine is used for the support strings.  A non-slip knot should be used  to loosely attach the string base of each plant.

Figure 1.  Diagram of Umbrella  Training System

An alternative is to attach the string to a tightly drawn horizontal wire centered on the row just above the top of the containers or the surface of a soil bed.  This avoids use of a knot around the stem which may be too tight.  Support strings are attached a week or so after transplanting, when vertical growth is beginning.  As the plant grows, the main stem is loosely wound around the string for support.  Special plastic clips may be used to attach the stem to the string just below the point where a leaf joins the main stem as a means of assuring the plant does not slide down the string as the fruit load develops.

Most growers prune their plants by the umbrella system (Figure 1).  In this system, all lateral branches are removed as they develop until the plant reaches the overhead support wire.  There , the terminal bud is removed after the second leaf above the wire and the last two lateral branches are allowed to grow.  These laterals are trained over the wire and allowed to grow downward to about 3 feet above the ground.  Fruits should not be allowed to develop on the lower 30 inches of the main stem to encourage the plantŪs rapid vegetative development.  Main-stem fruits above that point are allowed to develop at the base of each leaf.  Vigorous plants will continue to produce fruit on the downward growing laterals, although rate of production tends to slow down following harvest of the main stem fruit.

More than one fruit may begin to develop at each node.  Some growers thin these to a single vigorous fruit, but it may be more practical to leave all young fruits attached, because it has been observed that more than one may mature.  This occurs frequently, and there is no evidence that growth of two fruits at a node is slower than that of a single fruit.  Fruits more than slightly curved or whose shape is distorted in other ways should be removed immediately.


 

Fertilization and Irrigation

Greenhouse cucumbers grow quickly and should never be allowed to suffer from lack of water or nutrients.  The nutrient uptake rate by greenhouse cucumbers is very high.  One study indicates that an acre of cucumbers (8,000 plants) may require in the range of 25 pounds of nitrogen, 5 pounds of phosphorus, and 35 pounds of potassium per week during peak fruit production.  Fertilizer management practices will, therefore, have to be planned to assure that plant requirements are satisfied to achieve good yields of high-quality fruit.  Methods and fertilizer materials used to supply plant nutrients vary with the growing system used and grower preference.  The following guidelines will be helpful in planning the fertilizer program.

For growth in soil beds, apply all of the potassium and phosphorus needed and a small amount of nitrogen before planting.  Reasonable amounts of pre-plant fertilizer to apply per acre are 50 pounds of nitrogen (N), 150 pounds of phosphorus (P2O5), and 250 pounds of potassium (K2O).  Any micronutrient deficiencies, indicated by soil or plant analysis, should be corrected by incorporating minor element materials into the soil before planting.  Minor element deficiencies discovered during crop growth must be treated with foliar sprays.  Animal manures, used as a pre-plant fertilizer, can supply part of the nutrients needed, but only about one-third of the nitrogen and phosphorus in them becomes available to the plants during the growing season.  Excessive use of manures will increase soil salinity and retard plant growth.  For soils that are acid due to fertilizer use or natural soil conditions, lime and other nutrients may be required and will need to be incorporated before planting.

During crop growth, the most important element needed is nitrogen.  It should be supplied in the irrigation water at each irrigation, from soluble fertilizer materials, such as potassium nitrate (13 percent N), calcium nitrate (16 percent N), or ammonium nitrate (33 percent N).  The most efficient method of supplying water and nitrogen to soil beds or sand culture is through a drip or trickle irrigation system.  During the first few weeks after transplanting, apply 5 to 10 pounds of nitrogen per acre per week during fruit production.

In soilless systems, plants can be grown with a complete nutrient solution alone, with a complete N-P-K slow-release fertilizer (at rates of 1 to 2 pounds N per cubic yard, depending upon release characteristics of the product) or with a combination of the two materials.  When used in combination, rates for each material should be reduced by 30 to 40 percent.  Nutrient solution is applied, in the case of bag culture, at every irrigation through spray sticks or spaghetti tubes, or in sand culture, through a drip irrigation tube.  Frequency of application will depend upon plant size and greenhouse temperature, but will vary from once or twice daily immediately after transplanting to several times per day on warm days during harvest.  The irrigation volume required varies from 1 to 4 quarts per plant per day.  At each irrigation, a sufficient volume of solution should be applied to wet all of the growing medium particles in the plant root zone; allowing about 10 percent leachate.

 Critical levels for nutrients in plant tissue have not been determined for greenhouse cucumbers, but the following ranges are frequently found in apparently healthy plants and may act as guidelines.  Nitrogen, phosphorus, potassium, calcium, and magnesium concentrations are determined from petiole analysis.  All other elements are determined from blade analysis.


 
Element Concentration in Tissue
NO3-N 25,000-30,000 ppm
PO4-P 8,000-10,000 ppm
  10-15%
Ca   1-3%
Mg  0.3-0.7%
Fe   90-120 ppm
Zn  40-50 ppm
Cu 5-10 ppm
Mn  50-150 ppm
Mo 1-3 ppm
40-60 ppm

Yields, Harvesting, and Storage

Harvest fruit after it has reached a uniform diameter throughout its length, but before any yellowing appears at the blossom end.  Fruit generally grows to market maturity 12 to 15 days after the flower opens.  Fruit should not be left on the plant after it has reached marketable size to avoid retarding development of younger fruit.  Harvest frequency should be every 2 to 3 days.

Cucumber yields depend mainly on length of harvest period, as well as plant spacing, pruning practices, available light, prevailing temperature, variety, and good nutritional and pest management.  Considering these variables, yields range from 1 - 1 ½ to 3 pounds of fruit per plant per week, during midharvest on an umbrella trained crop.  Twenty to twenty-five fruit may be expected over a 10 to 12 week harvest period.

After harvest, the thin-skinned fruit is highly susceptible to softening because of moisture loss.  As soon as possible after harvest, fruit should be placed under conditions that will prolong its storage life.  If you must temporarily delay packaging and storage, keep the fruit in covered containers out of direct sunlight.  Individually package fruits in shrink-wrap film before packing in cartons to prevent moisture loss and to maintain quality.  The best storage temperature is 55 degrees F, with a relative humidity of 80 to 90 percent.  Storage at lower temperatures produces chilling injury, which reduces quality and shelf life.


 

Physiological Disorders, Diseases, and Insects

 Virus diseases (cucumber mosaic and watermelon mosaic) can seriously affect greenhouse cucumber production.  No variety currently available is resistant to these diseases.  Because aphids transmit mosaic viruses from other susceptible crops and weeds outside the greenhouse, it is important to locate the greenhouse at least one-half mile from susceptible field crops and to keep weed growth nearby under control.  The physical barrier of the greenhouse structure may offer some assistance in preventing entry of some insects, but should not be considered as a deterrent to the entry of virus-carrying aphids.

Powdery mildews (Sphaerotheca fuligenea) can seriously affect plant growth and fruit quality.  Resistant varieties are available and should be used where this disease has been a problem.  Control measures should begin when the first few spots of the fungus are noticed.  Powdery mildew occurs as small, white, dusty-looking spots about 1/4 inch in diameter, usually appearing first on the upper side of the lower leaves.

Gray mold (Botrytis cinerea) occurs when humidity is not properly controlled.  Fortunately, this disease can be completely prevented by providing adequate air circulation and a greenhouse climate that prohibits condensed moisture from collecting on plant surfaces.

Post-emergence damp-off (Pythium sp.) can be a serious problem in cucumber plantings.  The symptoms are a softening and yellowing of stem tissue at the soil line, followed by wilting.  Young plants are highly susceptible within a few days following transplanting, but the disease can also retard growth if infection occurs on maturing plants.  Good sanitation practices and sterilization of the growing medium before planting will prevent damp-off.

Crooking, a serious physiological disorder, results in decreased yields and reduced quality of greenhouse cucumbers.  Curvature in fruit begins at an early stage--often when the ovary is less than ½ inch long--and remains throughout maturity.  Slight curvature (up to 1 inch per 12 inches of fruit length) is tolerable in first-grade fruit, but excessive curving or crooking reduces market value.

Crooking has several causes.  Curvature can begin when a leaf or stem interferes with the lengthening growth of a young fruit.  Severe curvature sometimes occurs when a flower petal becomes stuck on the spines of a leaf stem or another young fruit.  An insect, such as thrips, feeding on one side of a young fruit, is known to produce crooking.

Adverse temperature, excessive soil moisture, and poor nutrition have also been suggested as causes.  Remove severely curved fruit from the plant as soon as possible.

Insects troublesome to greenhouse cucumbers include white fly (Trialeurodes vaporarium), two-spotted mites (Tetranychus urticae), vegetable leaf miner (Liriomyza sativae), cabbage looper (Tricoplusia ni), and greenhouse thrips (Heliothrips haemorrhoidalis).

The greenhouse environment is attractive to these pests and the grower must be constantly on the alert for developing populations.  Insects gain entrance to the greenhouse enclosure through vents, fan housings, open doorways, small openings in the walls or roof, and on clothing or equipment.  Regular inspections of plants are necessary to detect the presence of insect infestations and to apply control measures before serious plant damage occurs.

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