Greenhouses: An advantage for organic growers

field organic production of specialty crops in florida is very challenging due to the high pest pressure in the tropical and subtropical climate. greenhouse production, especially with soilless culture techniques, might provide growers with a viable system for becoming a consistent supplier of specialty crops year round for the organic market. 

By Robert C. Hochmuth

Greenhouse vegetables and herbs in Florida are produced on nearly 100 acres. Various soilless media are used in these greenhouses for production including perlite, peat, composted pine bark, rockwool and many other combinations of these products to form a custom mix.

Some of these products can also be used in a certified organic production system. The current chemical fertilizer programs used, of course, cannot be used in organic production systems. The development of an organic fertilizer program for soilless culture in greenhouses could open a new market for growers.

The organic food section in most grocery chains in the U.S. is one of the fastest-growing sections of the produce sector, increasing by as much as 20 percent per year over the last decade.

Field organic production of specialty crops in Florida is very challenging due to the high pest pressure in the tropical and subtropical climate. Greenhouse production, especially with soilless culture techniques, might provide growers with a viable system for becoming a consistent supplier of specialty crops year round for the organic market. 

Benefits of a greenhouse

Greenhouses offer organic growers a more controlled environment for managing the crop, including containing biological pest control agents inside and protecting the crop from weather problems, including extreme temperatures and rainfall. These same advantages have driven the increase in greenhouse hydroponic production of vegetables and herbs worldwide allowing high quality greenhouse produce to be available year round for the conventional produce market.

A conventional field grower can become a certified organic grower, but must have a three year transitional period in those fields to become fully certified. New greenhouse construction using a soilless production system could become certified in the first year since the production is not in the conventional soil. Existing greenhouse space in conventional production must also have a transitional period, even if in a soilless system.

According to a 2001 U.S. Department of Agriculture Economic Research Service report, an estimated 2000 acres of organic production is certified in Florida, compared to over 40,000 acres in California. Essentially all of that certified acreage is produced in the field.  Most certified organic production is in a soil-based system that utilizes crop rotations, building soil organic matter and soil health, green and animal manures. 

The native soil under a greenhouse in Florida makes that traditional organic system especially difficult because key principles such as crop rotation are not available. The availability of soilless mixes that can be components in a certified organic program allows greenhouse production to create new opportunities for growers.

Challenges of a greenhouse

The challenge in this system is providing proper crop nutrients in the correct amount and time. Initial research at the University of Florida/Institute of Foof and Agricultural Sciences’ North Florida Research and Education Center-Suwannee Valley (NFREC-SV)is being conducted to determine how growers can develop such a nutrition program for vegetables and herbs in soilless systems. The fertilizer materials accepted for use in an organic production system are listed on the Web site for the Organic Materials Review Institute (www.omri.org/).

Fertilization programs for organic production in a soilless system are difficult to develop because of a limited number of specific individual nutrients that can be used. The fertilizer program must depend upon a complete organic fertilizer material, usually made from composted animal wastes and other ingredients. This type of material can serve as the basis of the fertilizer program but must be fine tuned with additional nutrients supplied by other organic sources.

Organic fertilizer materials such as those made by Fertrell and Griffin Industries (Nature Safe) have performed reasonably well in initial trials at NFREC-SV. Programs to supply nutrients to leafy green vegetables and herbs will likely be much easier to develop than for fruiting crops like tomato, pepper, cucumber and strawberry. Many of the complete organic fertilizers also have a very high salt index and therefore cannot be over applied. This initial work suggests additional research is needed to refine this type of approach in a soilless system.

The other major aspect of greenhouse organic production is the entire area of pest control. The greenhouse provides a great opportunity by being able to exclude many pests and control the environment inside the greenhouse to reduce disease pressures. Many biological control agents are commercially available and could be important in controlling pests in a certified organic production area.

The whole area of combining greenhouse soilless and organic production has been a controversial area. Some feel as though organic production must involve the soil. The National Organic Program (www.ams.usda.gov/nop), which was fully implemented in October 2002, standardized what will be allowed from state to state. Soilless organic systems can be certified under the current rules of this program. Of course, a final certification reviews all of the systems and practices used on the farm. 

As a result, be sure to contact a certifying agent before planning your system.  A list of current certifying agents is available at the National Organic Program Web site.

Robert C. Hochmuth is a multi-county UF/IFAS extension agent based at NFREC-SV, (386) 362-1725. E-mail is bobhoch@mail.ifas.ufl.edu.