Organic Greenhouse Tomato Production

Abstract

This publication offers an overview of organic greenhouse tomato production. To be successful, the small-scale producer needs to do thorough production and marketing research, find or create a niche market, and produce a consistently healthy crop. Maintaining optimum fertilization and moisture levels, practicing rigorous pest management, and ensuring good pollination can increase crop yields. Information in this publication includes organic management methods for major diseases and insect pests; organic fertilization recommendations; a list of organic fertilizer suppliers; and a directory of further resources available on the Internet.

Table of Contents

• Introduction
• Education is Key
• Marketing
• Scheduling the Crop
• Soil and Soilless Media
• Pest Management
• Resistant Varieties
• Nutrition
• Grower Profile
• Pollination
• Summary
• References
• Resources
  • Organic Fertilizer Distributors
  • Information on the Web
• Appendix One: Problems in the Greenhouse
• Appendix Two: Recommended Fertilization Practices for Producing Organic Greenhouse Tomatoes

Introduction

Tomatoes are the leading greenhouse vegetable crop in the United States and Canada. In the U.S., the total acreage in greenhouse tomato production increased by 40 percent between 1996 and 1999. Statistics for 1999 show that the U.S. had about 800 acres in greenhouse vegetable production, with tomatoes accounting for 750 of those acres.(1) The leading states in greenhouse vegetable production are California, Florida, Colorado, Arizona, Ohio, Texas, and Pennsylvania—each with more than one million square feet in production.(2) The vast majority of greenhouse tomatoes are produced in greenhouses using conventional production systems. Conventional and organic greenhouse production differ in the types of potting media, fertilization practices, and pest control methods they use.

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Education is Key

Education is the first step toward a successful greenhouse tomato crop, and there is a lot of information available on growing greenhouse tomatoes. Your local extension agent is an excellent source of information for your area. Extension publications from all U.S. states are available on the Internet. Most publications can be downloaded and printed at no charge. California, Colorado, Florida, North Carolina, Georgia, and Mississippi all have excellent information on growing greenhouse tomatoes. Dr. Mary Peet's Greenhouse Vegetable Production Website is an especially good resource with links to many related websites. This website offers valuable information on sustainable production and integrated pest management, with specific information on individual crops. Mississippi State Extension Service has many publications and articles on greenhouse tomato production written by Dr. Rick Snyder. This website focuses mainly on conventional greenhouse production; however, much of the information is valuable to both organic and conventional growers.

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Marketing

Sell your tomato crop before you plant it. It is important for small growers to explore niche markets such as selling directly to the public via roadside stands or at farmers' markets. Marketing your products as "locally grown" is a possible strategy to explore. It may also be feasible to wholesale your product directly to local and regional retailers that sell organic produce.

Direct market sales are affected by competition among local greenhouses and by cut-rate wholesale organic produce. The market can change rapidly, and greenhouse producers must be adaptable to change. The popular press and advertising can have a powerful influence on consumers. Niche markets can fade overnight with the arrival of large wholesale operations or simply by a change in consumer demand.(3) For more information, request the ATTRA publications Direct Marketing and Organic Marketing Resources.

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Scheduling the Crop

Greenhouse tomatoes bring the highest price from December through April, when it is too cool for local field-grown tomatoes. Winter growers may choose between a one- or two-crop system. With the one-crop system, plants are set in September and grow through the winter and spring until late June. This system works best in the cooler and less humid northern regions and is also used by most Florida growers. In a two-crop system, the fall crop is succeeded by a spring crop. Tomato plants that have been growing since September do not have the same vigor as the younger transplants. The older plants tend to have a denser growth by winter, which reduces airflow and aggravates problems with humidity. Plants held over winter are more likely to be infected with diseases that thrive on high humidity and cooler temperatures, such as Gray Mold (caused by Botrytis cinerea) and Leaf Mold (caused by Cladosporium fulvum).

In a two-crop system, the fall crop is seeded between July and September. Check with your local extension agent for planting times in your area. If the crop is planted too early, high summer heat can stunt the young plants and delay harvest. For premium prices, try to schedule the first harvest to coincide with the first frost in your area. In some southern states, first frost may come as late as mid-November to early December.

Seed the spring crop in mid- to late November. If possible, the seedlings should be started in a separate house, in case there is a disease or insect problem with the fall crop. The seedlings will be ready to transplant about six weeks after seeding. Expect to see the first harvest in late March or early April. The spring crop is usually grown until the summer crop of field tomatoes is ready to harvest.(3)

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Soil and Soilless Media

Greenhouse tomatoes can be grown in soil or in soilless media. In soil culture, crops are grown at ground level or in raised beds. The soil is usually amended with approved compost and other approved organic additives. The potential for disease and nematode build up in organic soil-based greenhouses is quite high in many areas. Tomatoes, in particular, are vulnerable to many soil-borne diseases, including Verticillium and Fusarium wilts. Nematodes that can cause root knot galling can also be a problem in some soils. Many growers go to the added expense of grafting onto disease and nematode resistant rootstock. Steam pasteurization and solarization in the summer are approved pest control methods for nematodes, Verticilium, Fusarium, and other soil-borne pathogens.

Soilless cultivation methods—sometimes collectively (and loosely) known as hydroponics—are covered in the ATTRA publication Greenhouse and Hydroponic Vegetable Resources.

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Pest Manangement

One key to a successful organic greenhouse operation is maintaining rigorous pest management. A pesticide-free greenhouse means that growers must practice good sanitation and pest management methods from the beginning. Pathogens or insects can become epidemic in a greenhouse environment in a very short time. Once a pest problem has set in, there are few options available to organic greenhouse producers. For detailed information on specific greenhouse tomato pests and controls, see Appendix One. Integrated Pest Management (IPM) is a strategy that can be used in organic production as well as in conventional production systems.

IPM promotes a variety of tactics, including the use of pest resistant varieties and biological, cultural, and physical controls. Pesticides are a control tactic used in IPM, but they are used only when needed. Pesticide use is thus minimized without jeopardizing crop quality or yield. Organic production systems use all of these, with the exception of chemical pesticides. Other pesticides, such as insecticidal soaps, biopesticides, botanicals, and mineral-based pesticides, are allowed. For more detailed information on greenhouse IPM, refer to the ATTRA publication, Integrated Pest Management for Greenhouse Crops.

Cultural Control Methods

In a closed environment, some diseases can literally spread overnight. Pathogens come in contact with the plants in many ways. Infested soil or plant debris, air movement, water, and contaminated hands, tools, or clothing can all spread disease. Good ventilation and air circulation, rigorous sanitation practices, and maintaining optimum temperatures and humidity levels are effective methods of disease control in the greenhouse.

Sanitation

Rigorous sanitation practices are essential for healthy and productive crops. Before a crop is planted, it is important to thoroughly inspect the greenhouse. Screens, doors, and walls should be checked periodically for any tears or other openings. Mulching around the plants and using landscape fabric on walkways helps to reduce weeds and soilborne pathogens. It is not advisable to store houseplants in vegetable production greenhouses. A seemingly healthy houseplant can be a vector for many diseases that attack vegetable crops.(4)

During tomato production, debris and cull piles are a prime source of many plant diseases. Promptly remove all plant debris from the greenhouse areas before an infection can take place. Work surfaces should be made of non-porous material, such as stainless steel, and sterilized after each use. Laundry bleach is an acceptable disinfectant, providing the residual chlorine levels in the bleach-water do not exceed those set by the Safe Drinking Water Act (4 ppm).

Proper sterilization of hands, feet, and clothing when moving from house to house greatly reduces cross-contamination. Before entering the greenhouse, hands should be washed in hot soapy water. For tobacco users (both smokers and chewers), a rinse of 1–3% trisodium phosphate prior to washing in hot soapy water is recommended to avoid the introduction of Tobacco Mosaic Virus (TMV) into the greenhouse. Because TMV can survive on clothing for long periods of time (up to 3 years in a darkened closet), it is important that clothing and overalls be changed daily and washed and dried at high temperatures. A shoe wash with a disinfectant-soaked mat at the entrance to the greenhouse will help eliminate pathogens brought in on shoes. Adding a small enclosed entry porch to the greenhouse provides a place to decontaminate shoes, tools, and equipment, and also helps keep out pests. In situations where there is a contagious disease such as bacterial canker, all tools, machinery, and electromechanical pollinators should be sterilized at the end of every row with ethanol or 0.5% sodium hypochlorite.(5)

Ventilation, temperature control, and humidity reduction

Temperature control and humidity reduction play a major role in maintaining greenhouse crop health. During the fall, winter, and spring, when the majority of greenhouse tomatoes are grown, high humidity and limited air circulation give many diseases an ideal growing environment. Moisture condensation creates humid conditions within the foliage, encouraging fungal and bacterial infection.(6)

Good ventilation and proper temperature control are critical for reducing humidity and controlling airborne fungal diseases. To ensure good ventilation, allow several feet of airspace above the plants and use proper spacing between them. Pruning the suckers just below the first fruit set also helps to maintain good air circulation within the canopy. To increase ventilation, Mike Collins of Old Athens Farm in Westminster, Vermont, culls the bottom leaves once his plants are four feet tall. Collins cuts the leaves off an inch away from the stem and snaps off the stubs at the next pruning to minimize Botrytis infection sites.(7) Some greenhouse producers also "lower" their crop—move the plants on their supports, so the sections ready for harvest are always at the same level, enjoying the same temperature.

Temperature control can be maintained in several ways. Polyethylene tubing works best for maintaining even temperatures throughout the greenhouse. With this system, fresh air from the outside can be warmed with fan-type heaters to maintain optimum temperatures. Fans inside the greenhouse, mounted above the crop, help keep temperature uniform. With a pad and fan system, the air can be too cool at the cooling-pad end and too warm at the fan end. Temperature differences of 10–15ºF can occur within the same greenhouse, which can cause catfacing, uneven growth, failures in fruit set, and devastating foliage disease.(6) And the higher the humidity, the less efficient evaporative systems are. For even heating from the ground up, heating pipes can be placed between alternating rows. The heated air rises and pushes the cooler air to the floor, helping to maintain good airflow. In hot climates, greenhouses need higher roofs to keep hot air away from the plants.

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Resistant Varieties

Using disease-resistant seeds and transplants whenever possible is one of the organic greenhouse producer's best lines of defense. For best results, use good- quality seed from a reputable source. Organic growers must use organically grown seed if it is commercially available, or untreated seed from a conventional source if it is not. For a list of organic and untreated seed and transplant suppliers, see ATTRA's Suppliers of Seed for Certified Organic Production .

To indicate disease resistance, a series of abbreviations is usually listed with the description of the cultivar. Each abbreviation stands for a specific pathogen. For instance, Tobacco Mosaic Virus is TMV; Fusarium Wilt race 1 is F1, etc.(8) Fusarium Crown and Root Rot may be printed as FCRR or FrWi depending on the distributor. See Table 1 for examples of major greenhouse tomato diseases and their abbreviations. See Table 2 for a list of resistant greenhouse tomato varieties.

Once a variety of tomato has been selected, the next task is to decide whether to grow transplants from seed or to purchase plugs. Either way, all transplants must be grown using approved organic methods and inputs. The advantages of producing plugs in-house include an efficient use of greenhouse space and rapid production. The disadvantages include extra labor cost for seeding and transplant production and increased heating costs in winter (plugs are very sensitive to temperature fluctuations). There are many issues to consider when deciding whether to use seed or transplants. The size of the operation, available labor, and cost of production are just a few considerations. According to Kessler and Behe (9):

The decision should be based partially on market considerations, labor availability and expertise, the number of plants to be produced, the cost per plug, and the specialized equipment and facilities required. This investment is often not economically practical unless production is large or plugs are marketed to other growers. For most small to medium sized growers, especially [beginners], it is often more economical to purchase…plugs from specialized growers and concentrate on producing finished containers. The issue of grow versus purchase should be reviewed periodically as the needs and facilities of the grower change.

For more-detailed information on plug production, see the ATTRA publication Organic Plug and Transplant Production.

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Nutrition

A well-fed plant is a healthy plant. Maintaining optimum nutrient, light, and moisture levels will result in healthier plants that are better able to fend off diseases and insect pests. Tomatoes are heavy feeders because of their rapid growth and long production season. Tomatoes need 75 to 100 pounds of nitrogen (N) per acre and moderate to high levels of phosphorus (P) and potassium (K) for maximum yields. Soil tests can establish what nutrients soil needs. Some growers add a mixture of animal meal by-products, rock phosphate, and kelp meal to provide needed nutrients. Fertilizer efficiency is highest at a pH of 6.0 to 6.8. To help maintain proper nutrition and pH levels, a pH meter is a handy tool. For more information on organic fertilizers and the nutritional needs of tomatoes, see the ATTRA publication, Organic Tomato Production.

According to the National Organic Standards, it appears that organic greenhouse crops may be grown either in soil or in soilless media. Building nutrient-rich soil in a greenhouse environment takes extra time and effort, but the results are well worth it. Compost is the main nutrient ingredient used in soil beds. One grower in Canada applies compost at a rate of one or two cubic meters per 100 square meters of bed space (1.2 to 2.4 cubic yards per 1,000 square feet). The beds are then covered with straw mulch. Five to six applications were added to the beds at five- to six-week intervals in the first year. The compost was applied in smaller amounts and less frequently through the fourth year. A rich, healthy soil was the result. Soil organic matter usually ranges from 10 to 12% and can even reach a remarkable 25 to 30% after several years. For more information on large-scale composting, see ATTRA's Farm-Scale Composting Resource List.

Soilless technology shows promise for increasing yields and reducing economic losses to soil-borne diseases. Dr. Mary Peet and Janet Miles of North Carolina State University have recently concluded a study to develop organic fertilization regimes specifically for greenhouse tomatoes using soilless media. See Appendix Two for a copy of the article, "Recommended Fertilization Practices for Producing Organic Greenhouse Tomatoes" by Janet Miles. This article includes detailed recipes for each stage of maturity.

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Pollination

Tomato plants have both male and female reproductive organs on the same flower, so with a little help, each flower can self-pollinate. In the natural environment, wind and insects pollinate tomatoes. In a greenhouse environment, more attention must be paid to the pollination process to ensure maximum fruit set. Today, tomatoes are pollinated in greenhouses either by bumblebees or by mechanical pollinators.

Mechanical pollination is done with a battery-powered, hand-held pollinator or by electric vibrating benches. The hand-held pollinators are labor-intensive. Workers have to hand pollinate each plant two or three days each week during flowering. Vibration benches work on an automatic timer and do not require much labor after installation, but they are expensive and not cost-effective for small- to medium-scale growers.

Mechanical pollination of tomatoes was predominant in U.S. and Canadian greenhouses until the mid-90s, when the use of bumblebees was adopted from European growers. Today, most greenhouse tomato growers in North America are using bumblebees, which work every day of the week, selecting only the flowers that are ready to pollinate. Bumblebees can pollinate up to 30 flowers a minute. It is not unusual to have 100% pollination, which results in higher yields than are achieved with mechanical methods.(10)

Bumblebees are mild-mannered and easy to work with; they rarely sting without provocation. They start a new colony each year, with only a single queen hibernating over the winter. This queen then starts a new colony in the spring. By mid-summer the colony can number in the hundreds. At the end of the summer the bees begin to die out and the process starts over again. However, due to breakthroughs in bumblebee breeding, full-strength colonies of bumblebees are now available year round.

For commercial production, the bees are shipped by airfreight and placed in the greenhouse as the first flowers begin to open. Stocking rate varies from one hive for a small greenhouse to two to four hives per acre for larger facilities. The hives are usually replaced every 8 to 12 weeks as the colony begins to die out. There are two primary species of bees produced in Canada and the United States: Bombus occidentalis for the west and B. impatiens for the east. According to the USDA and AgCanada, the dividing line is at the 100th meridian, which runs through the middle of Texas, Oklahoma, Kansas, Nebraska, and the Dakotas. To avoid confusion, the USDA has classified these states as "eastern" states in the case of bees. Bees West, Inc., supplies western species, and Koppert Biological Systems, Inc., supplies eastern species.(10)

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Summary

A successful organic greenhouse tomato operation will require research into all aspects of the business. Before planting the first seed, it is important to locate a niche market in your area and schedule harvests to coincide with times of high market value. Soil systems have many advantages compared to soilless systems; however, they can be sources for soil-borne diseases such as Verticilium and Fusarium wilts. Maintaining rigorous pest control is key to maintaining a healthy, productive greenhouse operation. Successful pest control includes incorporating Integrated Pest Management practices, including cultural control methods, and the planting of disease resistant varieties. Organically grown seed must be used if available. If not, commercially available untreated seed may be used. All transplants, whether purchased or grown on the farm, must be grown using approved organic methods and inputs. Maintaining proper pH and fertilization levels improves disease resistance and increases yields. Using bumblebees for pollination can also increase yields and reduce labor costs.

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References

1) Snyder, Richard G. 1995. Greenhouse Tomatoes—The Basics of Successful Production. Proceedings of the Greenhouse Tomato Seminar. August 3-4, 1995. Montreal, Quebec, Canada.

2) Census of Agriculture. 1997. U.S. Census of Horticulture Specialties. Bureau of the Census, U.S. Department of Commerce, Washington, D.C.

3) Snyder, Rick. No date. Greenhouse Tomato Handbook. Mississippi State Extension Service. http://msucares.com/pubs/publications/p1828.htm.

4) Dr. Craig Anderson, Horticulture Extension Specialist, University of Arkansas, Personal communication, June 2001.

5) Jarvis, William R. 1992. Managing Diseases in Greenhouse Crops. The American Phytopathological Society, St. Paul, Minnesota. p. 148–149.

6) Wittwer, S. and S. Honma. 1979. Greenhouse Tomatoes, Lettuce & Cucumbers. Michigan State University Press, East Lansing. p. 72.

7) Grubinger, Vernon P. 1999. Sustainable Vegetable Production from Start-up to Market. NARES. New York, New York. p. 229–233.

8) Sanders, Doug. 1999. The Perfect Variety. American Vegetable Grower. Vol. 47, No. 12. p. 47-48.

9) Kessler, J. and Bridget Behe. 1998. Pansy Production and Marketing. ANR-596. Alabama Cooperative Extension.www.aces.edu/pubs/docs/A/ANR-0596/. 16 p.

10) Kueneman, Tom. 1995. The pollinator. Greenhouse Product News. Vol. 5, No. 9. p. 8, 10.

Resources

Organic Fertilizer Distributors

Agri-Growth International, Inc., www.agriorganics.com

Agri-Growth International, Inc. is a manufacturer of organic plant nutrients and stimulators. This website offers information on their products.Send e-mail to herb@agriorganics.com, or contact them at 1-780-484-0102 for a distributor listing in your area.

Alternative Garden Supply, www.alternativegarden.com/

Alternative Garden Supply offers a complete online store and a listing of retailers in your area. They carry a variety of liquid organic fertilizers such as Earth Juice, Fox Farm, Pure Blend, Maxicrop, and Age Old Organics.

Atlantis Hydroponics, 1035 Baxter Street, Athens, GA 30603, (706) 543-9980, Toll Free: (888) 305-4450, Fax: (706) 543-9919, info@atlantishydroponics.com, www.atlantishydroponics.com

Atlantis Hydroponics offers a wide range of organic fertilizers and stimulants: Alaska Start-up, Earth Juice, Fox Farm, Neptune's Harvest, Pure Blend, and others.

Greenfire, 347 Nord Ave. #1, Chico, CA 95926, (916) 895-8301, Fax: (916) 895-8317, www.greenfire.net/

Greenfire offers a wide range of organic fertilizers for both soil and soilless media. Greenfire is an Earth Juice distributor.

Growlight.com, sales@growlight.com, www.growlight.com/

Online catalog with a distributor list for retailers in your area. Organic products include B'Cuzz Growth, Root, and Bloom Stimulators; Nitrozime; and Age Old Organics Liquid Grow, Bloom, and Kelp.

Harvest Moon Hydroponics, www.hmoonhydro.com/

Harvest Moon Hydroponics offers a complete online store with a wide range of organic fertilizers and stimulants: including B'Cuzz, Earth Juice, Pure Blend, Superthrive, Nitron A-35, Grow Big, and Big Bloom. The website includes a list of Harvest Moon retailers in your area.

Home Harvest® Garden Supply, Inc., 3807 Bank Street, Baltimore, Maryland 21224, 1-800-348-4769, Voice: (410) 327-8403, Fax: (410) 327-8411,
ugrow@homeharvest.com, http://homeharvest.com/storeinfo.htm

Earth Juice, Fox Farm, and others.

HydroMall™, www.hydromall.com/infocart/Organic_Fertilizer/

HydroMall™ offers organic fertilizers from Agri-Growth International, Inc., such as: Myco-Net Biological Inoculum, Nutri-Max, and others. Order online from HydroMall™ or see their Stores Directory for a retail store near you.

Information on the Web

Budget for Greenhouse Tomatoes
Mississippi State University, Cooperative Extension Service
http://msucares.com/pubs/publications/p2257.pdf

Dr. Mary Peet's Greenhouse Vegetable Production Website
North Carolina State University
http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/resources/

Resource page with links to conversion tools, print information, and related Websites.

Environmental Control for Greenhouse Tomatoes
Mississippi State University, Cooperative Extension Service
http://msucares.com/pubs/publications/p1879.pdf

Florida Greenhouse Design
University of Florida, Cooperative Extension Service
http://edis.ifas.ufl.edu/scripts/htmlgen.exe?DOCUMENT_AE016

Greenhouse Tomato Handbook
Mississippi State University, Cooperative Extension Service
http://msucares.com/pubs/publications/p1828.htm

Greenhouse Tomato Production
Oregon State University, College of Agricultural Sciences
http://www.orst.edu/Dept/NWREC/tomatogh.html

Growing Hydroponic Tomatoes
The University of Arizona, College of Agriculture
http://ag.arizona.edu/hydroponictomatoes/index.htm

Tomato Disorders: A Guide to the Identification of Common Problems
Texas A&M University, Aggie Horticulture
http://aggie-horticulture.tamu.edu/tomatoproblemsolver/index.html

North Carolina State's Greenhouse Food Production Website
North Carolina State University
http://www.ces.ncsu.edu/depts/hort/greenhouse_veg/index.htm

Topics include cultural control, biological control, and organic production.

Starting A Greenhouse Business
Mississippi State University, Cooperative Extension Service
http://msucares.com/pubs/publications/p1957.htm

Starting Vegetable Transplants
Mississippi State University, Cooperative Extension Service
http://mscares.com/pubs/publications/p1995.htm

Texas Greenhouse Management Handbook
Texas A&M University, Aggie Horticulture
http://aggie-horticulture.tamu.edu/greenhouse/nursery/guides/green/

Tomato Plant Problems FAQ, by Kay Klier
http://is.rice.edu/~shel/tomato.html

An overview of tomato plant problems and organic cures.

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Appendix One: Problems in the Greenhouse

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