Last revised February 15, 2010
Mid-winter greenhouse tomato production is not generally recommended for western Oregon. Poor light intensity and high humidity often result in poor fruit set and quality. Effective lighting and humidity control is not considered to be economical. Heating and other production and marketing costs, and competition from outdoor production from California, Arizona and Mexico, and the availability of greenhouse tomatoes from Canada at competitive prices, make profitable greenhouse production in western Oregon difficult. Greenhouse production in British Columbia is possible because of their high inputs and the technical level of management possible in large operations (the trend is to shift to operations of over 2 acres), and the high quality glass greenhouses being used in the great majority of the operations, and their strong marketing organization.
Tomato is the most commonly-produced greenhouse vegetable crop. Although claims by greenhouse promoters are made that 30 or more lb marketable fruit can be expected per plant (or plant-space) per year, such production is only possible with very high inputs in quality facilities and optimal cultural practices. Production in western Oregon of 20 to 25 lb/plant space/year would be a more realistic top yield. A one crop schedule (December to December) is used by some Pacific northwest growers and is common in British Columbia, Canada. Growers there start their crop in January and harvest usually from March through November. A two-crop system is recommended under western Oregon conditions. This would consist of a fall (August to December) and a spring (January to June) crop. A two crop system is at less risk from crop pests and allows fruit set and harvest when environmental conditions are best and competition from outdoor productions is least.
Excellent references on greenhouse vegetable production are:
Greenhouse Vegetable Production Guide for Commercial Growers 1993-1994 Edition. British Columbia Ministry of Agriculture, Fisheries and Food., 808 Douglas St. Victoria, British Columbia, Canada V8W 2Z7.
Managing Diseases in Greenhouse Crops by Wm. R. Jarvis, American Phytopathological Society, 3340 Pilot Knob Road, St. Paul MN 55121-2097
A recent advance in greenhouse soilless tomato production is the Closed Insulated Production System (CIPS). Plants are grown in boxes that enclose the root system. The shoot extends through a seal in the lid. Capillary water movement in the reservoir is plant-driven and fertilizer diffuses from a fertilizer reservoir within a protected diffusion zone. This technique is still experimental but shows promise for single-cluster tomatoes. It is a concept that should be examined by those who are interested in controlled-environment tomato production.
Approximately 25,000 to 35,000 square feet of greenhouse tomato production is considered to be the minimum size economic unit. Smaller units are often used for part time production. In Oregon, total greenhouse vegetable production was just under one acre in 1994. This is similar for the state of Washington. A North Carolina publication reports that about 4000 square feet is considered enough production area to provide greenhouse tomatoes for about 10,000 people.
Variety selection is made to fit light intensity, fertility and disease resistance requirements. Check variety descriptions for diseases to which the variety is resistant, and the season to which it is best adapted. Size, color, lack of cracks and blemishes, shape, flavor, and productivity are all important factors in variety selection. Most field varieties do not perform well in the greenhouse environment.
Varieties such as Dombito, Belmondo, Boa, Jumbo, Trend, and Trust are best adapted to areas west of the Cascade Mountains and varieties such as Perfecto and Capello to areas east of the Cascades. Caruso, which has sparse foliage, is best adapted to fall cropping and may produce yellow-shouldered fruit under high light intensities. Some varieties may be too vigorous, and can become too viney under high water and fertilizer programs. Always test a variety in the season it will be produced before committing to it.
Varieties (in the 6.5-7.5 ounces fruit range) that have been used in the Pacific Northwest are: Capello, Cobra, Laura, Trust and Trend (all uniform ripening); Caruso (semi-green shoulder) Dombito and Jumbo (green shoulder). Varieties suggested for trial are: Belmondo, Boa, Carmello, Contento, Largetto and Match (all uniform ripening); also Dombello, Peto 109, Peto 656, Peto 761 (all green-shoulder). In all these varieties, provision for fruit set must be made (see section on "pollination" below).
Parthenocarpic varieties needing little or no mechanical vibration for pollination: Carpy, Quasar, Barry (these produce 4.0 to 5.0 ounce fruit) which may be too small for most domestic markets.
Tomatoes for the U.S. market must be of a large size. Many European varieties are not large enough. Know your market requirements for fruit color, size and shape, and the variety fruit characteristics before selecting the varieties to use. Fruit under 4 ounces is considered small, 4-6 ounce fruit is marketable, and fruit over 6 ounces (large) is preferred.
Plants have been commonly grown in well fertilized, well drained soil (ground- bed production). This conventional system is now largely replaced by a soilless culture system. Soilless culture utilizes totally artificial means of providing plants with nutrients and anchor. Major advantages are the elimination of the need for soil sterilization by steam or chemicals, and precise control of the application of nutrients and water.
Due to environmental concerns, restrictions may be in place regarding the disposal of excess fertilizer solutions and growing media. Possible options are to discard fertilizer solutions by using it on pastures or in other agricultural applications, and to recycle growing media by blending it with other potting mixes or agricultural soils. Consult appropriate agencies for available options.
Soilless culture is more demanding and less forgiving of mistakes than conventional soil culture. Good nutrient media composition and nutrient balance through the entire crop cycle are mandatory.
Soilless culture methods allow production of tomatoes in areas where suitable soil is not available or where disease or other conditions make ground production unfeasible. Although the system can be automated to minimize irrigation and fertilization labor input, continuous monitoring of most aspects of plant growth and culture media, nutrient balance, and a thorough understanding of the crop and its physiology is critical. Costs of the automatic devices and special nutrient media are substantial.
All other aspects of production remain the same as with conventional culture. There are little, or no yield or quality advantages over conventional production if the quality of management is equal.
Excellent books on this subject are:
Hydroponic Food Production by Howard M. Resh, Woodbridge Press Publishing Company, Santa Barbara, CA 93160.
A Guide for the Hydroponic & Soilless Culture Grower by J. Benton Jones, Jr., Timber Press, POB 1631, Beaverton, OR 97075.
Two major soilless culture systems are used, those in which plant nutrients are recirculated (closed-system hydroponics), and those that utilize artificial media for plants to anchor but new nutrient solution is constantly provided to the plants and the excess nutrient solution is not collected and recirculated (open-system hydroponics or bag culture).
Closed-system hydroponic culture is the growing of plants in troughs or tubes, where plants are anchored in gravel, sand, or artificial soilless mixes; or without artificial media for anchor, such as nutrient-film technique (NFT). Any system used must be suitably built to allow proper application and recirculation of the nutrient media. Flow rates of 1 1/2 to 2 quarts per minute are most common. In a closed-system, the nutrient solution is regularly monitored and adjusted for pH as needed. Because plants take up nutrients at different rates, and roots exude certain chemicals, imbalances and problems can occur. To prevent undesirable build up of certain elements, the nutrient solution may need to be changed every 2-3 weeks with changes as often as once per week during periods of peak growth. By careful monitoring of nutrients in solution and especially the electrical conductivity (EC) daily, and by installing activated charcoal filters to remove certain toxic root exudates, a large reservoir of nutrient solution may be maintained for one crop cycle (up to 10-11 months). The EC should be maintained at 2.5, so that fresh water is added when EC exceeds 2.5 and new, complete nutrient solution is added to bring the EC back to 2.5.
Bag Culture uses artificial media (usually rockwool) packaged in 3 or 4-cubic-foot bags. Rockwool comes in two densities, standard and low density. The low density is used for one year and discarded. The standard density may be sterilized and reused for up to three crops. Two common trade names are Redi-Earth and Metro-Mix. The 4 cubic foot bags are best for tomatoes. Two rows of tomatoes are usually planted per bag with plants spaced 16 inches apart in each row with rows 16 inches apart. Bags are placed in rows 6 feet apart, and spaced down the row to allow a uniform 16 inch spacing between plants. A drip irrigation system with spaghetti drippers for each plant is used to distribute the nutrient solution. A 10%-20% excess solution is applied during cloudy cool periods and 25% to as high as 50% under sunny, warm conditions to provide drainage and prevent salt buildup. This excess should be collected and discarded or may be reused with certain restrictions.
Common modifications of this system (to reduce cost) utilize 3-5 gallon plastic bags or pails with saw dust, pine bark or rice hull media. Western Hemlock and Douglas-fir are most commonly available and the main ones used in the Pacific Northwest. Avoid western red cedar because of possible toxicity from chemicals in it. Use a medium-fine grade of horticultural grade (guaranteed to be free of toxic chemicals that may be used by the lumber industry). If too fine a grade, the saw dust will limit oxygen exchange as it breaks down resulting in root suffocation. Prior to using saw dust, test leachate conductivity for any salt accumulation and leach bags with fresh water if needed. Modifications of the fertilizer program are necessary to compensate for specific media. Of particular concern is possible manganese toxicity since manganese can accumulate in wood to toxic levels. Check the first leaf tissue samples and adjust manganese applications as needed.
Hydroponic greenhouse promoters have often failed to present their product fairly and have created unrealistic expectations. None of the package offers of equipment and technical services guarantees success. Investigate thoroughly before making financial investments.
Greenhouse tomatoes are always grown from transplants. Use a special part of the greenhouse to grow these transplants. This can be a separate greenhouse, or an area divided off from the main greenhouse where day and night temperatures can be separately, and accurately maintained.
Plant the spring crop in early December, so harvest will begin in mid-March. For this crop, seed into flats, then transfer seedlings to 4-inch containers set close together when the first true leaf has formed. Space the containers at an 8 x 8 inch spacing two to three weeks later to finish growing the transplants. Set plants in their permanent location about mid February.
Although 3.5 to 4 square feet of space per plant is often used in other areas, about 4.5 to 5 square feet per plant would be more appropriate under western Oregon conditions. Plants should be trained to a single stem and supported by strings hanging from overhead wires.
Vines are usually removed by the end of July or early August when outdoor tomatoes become available locally. From seeding, it takes about 5 months for a spring crop to begin to fruit.
Plant the fall crop in mid-June, and set the plants in their permanent location about August 1. It takes about 3.5 to 4 months from seeding until first pick for a fall crop, which should begin in early October, after local tomatoes are no longer available. Aim for a production peak around Thanksgiving, terminating after Christmas or when heating costs and lighting conditions become limiting in December.
For more information on this subject, see the file Florida Greenhouse Design.
Accurate temperature, humidity, and carbon dioxide control are important. Environmental control is accomplished in many ways ranging from totally manual, to sophisticated computer-assisted control. Computers are also used to monitor fertilizer and water applications.
A major consideration in environmental control is that of providing temperature and humidity conducive to active movement of water and nutrients through the plant for optimum growth. This is done by maintaining a humidity of between 60 and 80% during daylight hours. In the Pacific Northwest, light intensity and duration are limiting factors in winter making the economics of supplemental lighting an important consideration. Light intensity is influenced by external factors such as cloud cover and fog and also the quality of the greenhouse covering and its condition. Dirt, dust, condensation and degradation of the covering material itself can seriously reduce yields.
If a greenhouse is to be kept closed for long periods (several days at a time) to conserve heat, you should provide suitable carbon dioxide generating equipment (see below). Management of irrigation to control increased humidity and control of increased disease problems also become critical in houses with reduced ventilation.
Temperature requirements for major greenhouse vegetables differ. In general, the cooler temperatures are used when light intensities are low. For tomatoes, days, 70 to 75 F; nights, minimum 62-65 F. Where day temperatures might exceed 85 to 90 F, cooling equipment is needed to prevent fruit set failure and to allow proper red color developing in the maturing fruit.
Tomato flowers form about 3-4 weeks before they become visible. The first flowers form about the time the seedling cotyledons unfold and the first true leaf is just visible. Research has shown that if tomatoes are subjected to a cold treatment at this time, the first cluster will develop sooner, there will be less leaves and shorter internodes to the first cluster, the cluster will have more flowers and set more and larger fruit. Varieties differ in their response to cold treatment. Some varieties may develop rough fruit in the first cluster after exposure to cold treatment, so always test the variety you are using before subjecting your whole crop to a cold treatment. Do not subject the variety 'Trust' to cold treatment for the reason just given.
Cold treatment consists of exposing seedlings at the time of cotyledon unfolding to continuous (day and night) temperatures of 52 to 56 F until the plants reach the two true leaf stage. This may take ten days to three weeks. Ten days are sufficient in sunny weather while up to 3 weeks may be needed during cloudy, winter weather.
Following cold treatment, night temperatures should be raised to 58-62 F and day temperatures should be maintained at 60-62 F during cloudy days, while 65-75 F should be maintained during sunny or partly cloudy days.
Carbon dioxide enrichment
Carbon dioxide is normally present in the atmosphere at a concentration of 300 parts per million (ppm). Carbon dioxide levels in greenhouse air may be depleted to levels that may limit plant growth, especially in tightly sealed greenhouses and when ventilation is restricted during daylight hours. Addition of carbon dioxide to greenhouses has been demonstrated to improve vegetable yields. Concentrations of 1,000 ppm. or more in greenhouse atmospheres have given the best results. Yield increases of 20% or more have been reported for tomatoes under certain conditions. Carbon dioxide generating and monitoring equipment is readily available. Flue gasses from certain types of heaters and fuels, and even liquid carbon dioxide are used. Investigate the various models and types before purchasing.
Concentrations should be adjusted for light intensity and growth stage as follows:
|Bright, sunny weather||1000 ppm|
|Cloudy weather||750 ppm|
|Young plants||700 ppm|
|During moderate ventilation||350 ppm|
Light intensity during seedling growth is directly related to the number of days to flower and yield. Low light intensities delay flowering and reduce fruit set and total yield. Under western Oregon winter conditions, light levels are not adequate for good commercial production. This is due to both the shorter days of winter and to frequent cloud cover and fog. Based on research from Canada, winter light conditions in western Oregon can be expected to result in as much as a 20-day delay in flowering and a 50% reduction in early yield for a crop intended for late winter and spring harvest. Supplemental lighting becomes very important during this period and also when plant populations are increased (and less than 4.5 to 5.0 square feet per plant is used).
High intensity discharge (HID) lamps, including high pressure sodium and metal halide lamps, are the only types that provide sufficient intensity and light quality for supplemental lighting. Although these may be used to supplement light during the day and/or to extend daylength, the economics of their use has not been determined. Note: Low pressure sodium lamps, such as the yellow-orange lights used in street lighting, should not be used due to the adverse effect that their light quality has on plant growth habit.
Light quality affects plant growth. Most high pressure sodium lights, designed to produce high levels of photosynthetically active radiation (PAR), tend to produce excessively elongated internodes. To compensate for this, metal halide lights that provide a greater portion of the blue spectrum may be added. Light placement and lighting schedules also affect growth and pollination.
Light intensity is a function of lamp wattage and distance from the plant canopy. About 650 footcandles at the leaf surface is considered the minimum intensity necessary for normal growth (for rough conversion purposes, multiply micromoles by 7 to get footcandles). With one design, a 1000-watt metal halide lamp covers approximately 112 square feet when 600 footcandles are desired. This translates to approximately 32 fixtures needed for a 30' x 120' greenhouse. Since each 1000-watt fixture gives off about 3750 BTU per hour, fuel savings would also be realized during the time the lights were operating. Growers must carefully evaluate supplemental lighting and test its efficacy under their conditions. Growers seriously considering supplemental lighting should also investigate the overall cost using 400-watt bulbs, even though more fixtures would be needed.
Although supplemental lighting increases yield under adverse sunlight conditions when all other production conditions (carbon dioxide, etc.) are optimal, the increased cost of installation, operation and maintenance of the lights and price competition from other tomato production areas makes the economics of supplemental lighting marginal in Oregon.
Painting all interior surfaces white and using a reflective white plastic ground cover between plant rows helps maximize light intensity within the greenhouse.
Commercial fertilizer mixes are available through horticultural supply companies. Tailor fertilizer programs for specific crops and soil fertility situations. Proper fertility is necessary for success. Plants have different fertilizer requirements during different stages of their growing cycle. Whether you use soil or a soilless system, no single set of recommendations will apply, so use soil tests to determine initial applications, and monitor fertility levels by leaf analysis throughout the growing season. Both soil tests and leaf analyses are available through Oregon State University Extension offices.
Conventional soil culture
A routine fertilizer program would be the addition of 0-20-20 fertilizer at 1,000 to 2,000 lb/acre before the fall crop, and 650 to 1,000 lb before the spring crop or, you can supply phosphorous by applying 46 percent triple super phosphate at 300 to 500 lb/acre and potassium by using potassium sulfate at 300 to 400 lb/acre.
Add N as ammonium nitrate, calcium nitrate, or potassium nitrate before planting and throughout the season, depending on the amount of organic matter in the soil. Feed weekly with solutions of balanced fertilizers.
Proper feeding of tomatoes with N is critical. Too much N when the plants are small will result in soft growth, small flower clusters, and poor set. Apply N in limited quantities before planting, at about 50 lb/acre, and apply weekly as necessary to maintain adequate N levels in the leaves. Nitrogen levels may be monitored by regular leaf-petiole analysis.
Micronutrients are normally provided by the soil's clay and organic fractions. Soil tests are necessary to determine which if any micronutrients must be added.
A number of soilless culture systems are available. These are variations of the "closed" or "open" systems described earlier. Fertilizer proportioners are used to accurately inject the proper amount of nutrient concentrate into the water stream used for irrigating the plants.
Choose a high quality fertilizer injection pump and system to minimize fertilizer distribution problems. Follow directions carefully in preparing and dispensing the nutrient solution. The major advantage of bag-culture, is the reduced management of nutrient solution monitoring, and the elimination of nutrient circulation, that is required in "closed" hydroponic systems. All major and micro-nutrients must be added, and kept in balance.
Totally soluble hydroponic fertilizer mixtures are available from regional horticultural supply houses. Follow manufacturer's recommendations carefully and completely as outlined specifically for tomatoes. Improper alterations of formulas or instructions for their use, can result in serious production problems.
Most commonly at least two stock tanks are needed to prevent insoluble precipitates from forming when the nutrients are mixed and injected. One stock tank is usually used to mix potassium nitrate, calcium nitrate and iron chelate. The other contains the phosphorous source, magnesium sulfate, potassium chloride and the rest of the micronutrients. This is done to prevent the formation of insoluble precipitates that most commonly occur from the mixing of calcium nitrate and phosphorous materials.
The use of more expensive "technical grade" fertilizer salts eliminates sludges from forming. Where "fertilizer grade" materials are used, sludges will form in the potassium nitrate, calcium nitrate tank due to insoluble additives used in these fertilizers to prevent caking and dust.
For a check on crop progress leaf samples should be taken at regular intervals beginning at about the time the third cluster begins to set. Sample the whole leaf with petiole, choosing the newest fully expanded leaf below the last open flower cluster. Sufficiency leaf analysis ranges for newest fully-expanded, dried whole leaves are*:
|Micronutrients (parts per million)|
|Before fruiting||During fruiting||Before fruiting||During fruiting|
|N: 4.0-5.0||3.5-4.0||Fe: 50-200||50-200|
|P: 0.5-0.8||0.4-0.6||Zn: 25- 60||25- 60|
|K: 3.5-4.5||2.8-4.0||Mn: 50-125||50-125|
|Ca: 0.9-1.8||1.0-2.0||Cu: 8- 20||8- 20|
|Mg: 0.5-0.8||0.4-1.0||B: 35- 60||35- 60|
|S: 0.4-0.8||0.4-0.8||Mo: 1- 5||1- 5|
Toxic levels for B, Mn, and Zn are reported as 150, 500, and 300 ppm, respectively*.
* Taken from J.M. Gerber 1985. Plant growth and nutrient formulas. pp.58-69. In A.J. Savage (ed.). Hydroponics Worldwide: State of the art in soilless crop production. Int'l Ctr. for Special Studies, Honolulu, Hawaii).
If mulches are used, apply to the soil when tomatoes are about two feet high. Straw mulch is most common, used at about 200 bales per acre. The mulch reduces evaporation of water from the soil and prevents compaction of the surface. White (reflective) plastic mulches are recommended to control weeds, conserve moisture, reduce humidity, and improve light conditions.
Maintain an adequate supply of water to plant roots. Excess water reduces soil aeration. Young plants put in the greenhouse in mid-winter May need to be watered only once every 10 to 14 days. The same plants in mid- summer may need water every two or three days in ground beds. A fall crop would need a total of about 15 to 18 inches; a spring crop may need 20 to 25 inches of water.
With bag culture, mature plants may need to be watered several times a day. One to 3 quarts per plant per day may be needed depending on growth stage and plant size.
Tomatoes are self pollinating under open field conditions. Pollen sheds and fertilization occurs as a function of normal air movement and its agitation of the plants and flowers. Under greenhouse conditions, flowers need to be agitated mechanically, or fruit needs to be set using plant chemical hormones that are sprayed on flower clusters on a regular basis.
A few new varieties have been developed that are parthenocarpic (need no pollination, and are seedless). These generally have small to medium size fruit and have not been tested adequately in the Pacific Northwest (see section on "varieties" above).
Pollination by mechanical vibration is recommended with the large fruited U.S. and European varieties. This is accomplished using a hand operated electric vibrator available from horticultural supply companies. These vibrators operate on 110 volt or battery power. The battery powered models use a 6 or 12 volt motorcycle battery. Units using flashlight batteries have insufficient action for best pollination. Many other methods have been tried or tested. None have been as good.
Timing is important when using mechanical vibrators to set fruit. Pollen sheds most readily when temperature is at its peak, and relative humidity lowest on a given day. The optimum time for that is between 11 a.m. and 3 p.m. during winter and early spring. Each flower cluster needs to be vibrated every day, as long as flowers are still opening in that cluster, to accomplish pollination of the flowers that open on that day.
Note: Special bees (bumble bees) are now being used for pollination. These bees mechanically agitate tomato flower clusters to acquire pollen and thus accomplish pollination. Currently, the high cost of obtaining these bees has limited them to use in very large interconnected greenhouse ranges. The bees would have to be obtained from special bee keepers.
Chemical fruit set is commonly used in European greenhouse tomato production on varieties that have been specifically developed to produce high quality fruit with this method. Most large fruited varieties used in the U.S. will develop hollow, soft and misshapen fruit with the use of chemical setting agents, therefore chemical fruit setting is not recommended.
Auxiliary branches must be pruned as the plant is trained to a single stem, supported by string to an overhead wire. In rare occasions, especially when grafted plants are used, plants may be trained in a double stem configuration.
With varieties that tend to produce small fruit, cluster pruning is used to increase fruit size, and limit the number of fruit per cluster. Generally, 3-4 fruit per cluster are allowed to develop with these varieties, with three fruit per cluster during the fall and winter cloudy weather and four during the sunny late spring and summer period. Fruit number per cluster is the factor that most affects fruit size, assuming other growth conditions are adequate.
To reduce the likelihood of disease spread (especially Tobacco Mosaic Virus), exercise careful sanitary procedures. Workers should use disposable gloves, disposing them, and sanitizing pruning instruments at the end of each row. No tobacco products should be allowed in the greenhouse, and users of such products must not handle TMV susceptible tomato varieties.
Blossom-End Rot: Varieties differ in susceptibility. Caused by calcium imbalance or deficiency during critical stage of fruit differentiation and expansion, usually induced by water stress.
Gray-Wall: Linked to high plant vigor, associated with high rates of nitrogen fertilization with high soil moisture and low temperature. In some cases certain bacteria, fungi and/or tobacco mosaic virus are thought to be involved in gray wall. Often associated with blotchy ripening (see below).
Blotchy Ripening: Promoted by low potassium levels in the fruit, high soil moisture and humidity and fluctuating temperatures during fruit ripening (above 85 F.) and low sunlight levels, or shaded areas in the plant canopy. Aggravated by compacted soils.
Solar yellowing: This problem occurs most commonly on fruit ripening in late May and June when days are longest, sunlight is most intense, and temperatures exceed 85 F. Under such conditions, lycopene (the red pigment in tomato) fails to develop normally in some varieties, leaving only the carotene (yellow) pigment to show at the shoulder or, with green-shoulder type tomatoes, where the dark green portion was. Even with temperatures under 85 F. the surface temperature of exposed fruit, especially those with dark green shoulders can become high enough to inhibit normal red color development. In other parts of the day or night, when temperatures do not exceed 85 F, some red color may develop, resulting in an orange, rather than a yellow abnormality. To reduce this problem, protect fruit surfaces from short-wave solar radiation by altering pruning practice in March and April by allowing two leaves to form on axillary branches rather than removing the axillary branches. The use of non-phytotoxic white wash will also help if applied when fruit are at the mature green stage. The white wash will have to be removed before the fruit is marketed.
Roughness and scars: Varieties differ in susceptibility. associated with large fruit. Particularly severe when young plants are exposed to cool temperatures, and night temperatures below 50 F. when flower clusters are differentiating.
Fruit cracks: Varieties differ in susceptibility. Promoted by fluctuations in soil moisture and temperature. Often seen when varieties developed for hot, arid climates are subjected to humid, wet conditions.
Yields from a two-crops-per-year system would be about 8 pounds of fruit per plant from the fall crop, assuming a 2 to 3 month harvest period ending in late December (0.8 lb/plant/week is considered very good). Approximately 12-15 pounds of fruit per plant may be realized from the spring crop assuming a 4 month harvest period ending just after the July 4th holiday.
Yield from a single-crop-per-year system, where harvest begins about mid October and ends in July the following year, could produce a total of about 25-27 lb/plant (based on 0.5-0.75 lb/plant/week). The lower output per week per plant shown is due to adverse winter climatic conditions (cloudiness and high humidity) generally experienced west of the Cascade mountains.
Fruit is harvested when mature green if it is to be held before marketing. Mature green fruit have well developed internal gel, and may have internal tissues that are beginning to turn red. Vine ripe fruit ranges from fruit just turning red to fully ripened, depending on market requirement. When harvesting and handling, avoid bruising fruit.
The USDA Grade Standards for Fresh Tomatoes recognize 6 official color designations:
1) Green - surface of the tomato is completely green;
2) Breakers - a definite break in color from green to tannish-yellow, pink or red on no more than 10% of the surface;
3) Turning- more than 10% but less than 30% of the surface, in the aggregate, shows change as in 2) above;
4) Pink- more than 30% but less than 60% of aggregate surface shows pink or red color;
5) Light Red - more than 60% of aggregate surface is reddish pink or red provided that not more than 90 % is red;
6) Red- more tan 90% of surface in the aggregate show red color.
Store mature-green tomatoes at 55 to 70 F; ripe fruit at 45 to 50 F and a relative humidity of 90 to 95%.
Mature-green tomatoes cannot be successfully stored at temperatures that greatly delay ripening. Tomatoes held for 2 weeks or longer at 55 F may develop abnormal amount of decay and may fail to develop a deep red color. The optimum temperatures for ripening mature-green tomatoes range from 65 to 70 F. Tomatoes will not ripen normally at temperatures above 80 F. A temperature range of 57 to 61 F is probably most desirable for slowing ripening without increasing decay problems. At these temperatures the more mature fruit within the mature-green range will ripen enough to be packaged for retailing in 7 to 14 days.
Fruit held below 50 F become susceptible to alternaria decay during subsequent ripening. Increased decay during ripening occurs after 6 days of exposure at 32 or 9 days at 40 F. Mature-green tomatoes may also be damaged by low temperatures in the field. A high percentage of tomatoes exposed to temperatures below 50 F for a week before harvest would probably develop alternaria rot even at recommended storage temperatures. Some loss due to chilling can be expected in fall-grown tomatoes exposed for over 95 hours to temperatures below 60 F during the week before harvest. Severity of chilling increases with increases in exposure time, so 135 hours exposure to below 60 F may result in heavy losses.
Chilling periods for fruit in storage and during transit, have a cumulative effect. Thus, fruit chilled for only a short period in storage can become very susceptible to decay when held for only a short period at chilling temperature during marketing. Tomatoes should be kept out of cold, wet rooms because in addition to potential development of chilling injury, extended refrigeration damages the ability of fruit to develop desirable fresh tomato flavor.
Semi-ripe tomatoes with 60 to 90% color can be held up to a week at 50 F. If held longer, they will probably not have a normal shelf life during retailing. Riper tomatoes will tolerate lower temperatures. For example, "firm-ripe" tomatoes can be held a few days at 45 to 50. Long holding of ripened tomatoes at low temperatures (40 and below) results in loss of color, shelf life, and firmness.
When it is necessary to hold fully-ripe tomatoes for the longest possible time before their immediate consumption upon removal from storage, as for example, for ship-board or overseas use, they can be held at 32 to 35 F. for up to 3 weeks. Such tomatoes, although acceptable, would not be of high quality and would have little if any shelf life remaining.
Fully ripe: When it is necessary to hold fully ripe tomatoes for the longest possible time before their immediate consumption upon removal from storage, as for example, for ship-board or overseas use, they can be held at 32 to 35 F for up to 3 weeks. Such tomatoes, although acceptable, would not be of high quality and would have little if any shelf life remaining. Mature- green, turning, or pink tomatoes should be ripened before storing at such low temperatures.
A storage temperature of 50 to 55 F is recommended for semi-ripe to fully ripe greenhouse-grown tomatoes. Ripening of less mature tomatoes at 70 F is recommended before storage at 50 to 55 F.
Research showed that an atmosphere with 3% oxygen and 97% nitrogen extended the life of mature-green tomatoes up to 6 weeks at 55 F and that the flavor of the ripened fruit had no off-flavor and was acceptable to the taste panel. A 1% or lower oxygen level can cause off-flavor. Increased carbon dioxide levels provide no benefit; in fact, levels of 3 to 5% have been reported to cause injury at 55 F.
One function of post-harvest handling in packing houses today is the washing, brushing and cleaning of produce to remove any pesticide residues that may be on the fruit. Tomatoes lend themselves well to such procedures.
Package tomatoes by size in 8 to10-lb, single layer cartons, or 20-lb double layers. Use only containers intended for greenhouse-produced fruit, and so designated. In general only top grade fruit is marketed. Greenhouse tomato fruit is usually individually differentiated with stick-on labels. Misshapen and defective fruit should be removed from vines as soon as it is so recognized.
Proper control of plant disease is critical in greenhouse environments, where high temperatures and humidity are ideal for diseases to develop. Insect and nematode infestations, too, can become rampant under the confined greenhouse conditions.
You can control most fungus and virus diseases with fungicides and proper sanitation and sterilization of soils, growth media, and equipment. The most serious fungus disease on tomatoes are leaf mold (Cladosporium), early blight (Alternaria), leaf spot (Septoria), gray mold (Botrytis), and the wilt diseases (Fusarium and Verticillium).
Tobacco mosaic virus can be serious and several other virus diseases may occur. Proper sanitation to reduce spread by workers, soil sterilization, and control of insect vectors are some of the methods of control.
Early control of white fly, aphid, and spider mite infestation is important. Several chemicals and a large number of biological controls are available to control these pests.
Note that Oregon law requires that agricultural pesticide use be reported to the Oregon Dept. of Agriculture through it on-line PURS system.
Nematodes may become a problem in either soil or hydroponic culture. Sterilization of soil or hydroponic media is used as a preventative measure. Current recommendations on pesticides are available from your county Extension agent. Always follow label instructions and safety precautions precisely.
See the PNW Plant Disease Management Handbook for information on disease management for greenhouse tomatoes.