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By David Kuack for Hort Americas' corporate blog:

"Organic fertilizers provide option to grow more sustainably"

Growers of both food and ornamental crops are facing increased scrutiny regarding their production practices from the pesticides they apply to the amount of water and energy they use. In October, Whole Foods Market launched its Responsibly Grown program. The company said the purpose of this new rating system is to assess production practices that impact human health and the environment. The system labels fresh fruits, vegetables and flowers as “good,” “better” or “best.” The program also prohibits the use of some of the hazardous neurotoxins still permitted in agriculture.

If growers implement more sustainable practices to produce their crops, are consumers willing to pay more for them? A recent University of Florida study focused on consumers’ willingness to spend more on ornamental plants based on plant attributes related to sustainable production methods, container types and origin of production. Consumers were willing to pay up to 16 cents more for plants grown using energy-saving and sustainable production methods, plants grown in non-conventional containers and plants grown locally.

Organic fertilizers show potential

Claudio Pasian, horticulture associate professor at Ohio State University in Columbus, said an increasing amount of pressure is being put on growers related to the environment by both retailers and consumers.

“Growers may be forced by their clients to produce more sustainable products, including more organic products,” Pasian said. “Here in Ohio, like in other parts of the country, there are concerns with fertilizers running off into waterways and leaching into ground water. In the future "fertilizer" may become a taboo word for some people. For some people, perception is reality. Using an organic fertilizer may help growers achieve a more sustainable image with retailers and consumers.”

Based on research Pasian has conducted on ornamentals plants and herbs, he said organic fertilizers look like a promising alternative to traditional water soluble fertilizers. Like any new product or technology, he said there are differences between traditional water soluble fertilizers and organic fertilizers and growers will have to learn how to use them.

Pasian began his research on organic fertilizers as a result of a substrate manufacturer seeking to conduct trials incorporating organic fertilizer into some of its consumer growing mixes.

“The company wanted me to run some experiments with a number of fertilizers,” he said. “There were no liquid organic fertilizers tested because the purpose of the study was to incorporate the fertilizers into growing mixes. All of the organic fertilizers tested were in a solid form, either a powder or small granules. Most of the organic fertilizers were animal-based. The control plants were treated with a 20-10-20 water soluble fertilizer at 100 parts per million nitrogen.”

Pasian said two of three annuals (seed geranium, pansy and petunia) grown with the organic fertilizers did very well. Although the organically fertilized plants were smaller in size, he said they were commercially salable.

Pasian found the only plants that occasionally did not do well with organic fertilizers were pansies. He has not conducted any further experiments to determine why there were issues with pansies grown with organic fertilizers.

“I’m not sure why the pansies did not do as well as the other species,” he said. “There were some phytotoxicity issues. The quality of the plants was not as good and there was high rate of mortality.”

Expanding fertilizer trials

After the initial trials with organic fertilizers showed positive results, Pasian expanded his research with additional ornamental plants. He compared incorporating Scotts Miracle Gro Organic Choice and Sustane organic fertilizers to a controlled-release and water-soluble fertilizers. All of the plants in the study were grown in 4½-inch pots containing Fafard 3B bark-based growing mix without a fertilizer charge.

“I grew six annual bedding plant species (angelonia, seed geranium, hypoestes, impatiens, pansy and petunia) with the different fertilizers,” he said. “The plant growth for plants fertilized with the controlled-release fertilizer and water soluble fertilizer were very similar. In most cases the water-soluble fertilized plants were the largest, followed by the controlled-release fertilizer and then the organically fertilized plants.

“The plants grown with the organic fertilizers were slightly smaller. But overall the organically fertilized plants did well. In some cases, the plants being smaller could be a positive effect because that means growers may not have to apply growth regulators.”

Trialing herbs and perennials

Pasian has received a grant from the Horticultural Research Institute to expand his organic fertilizer study to include herbs and perennials. He worked with a local grower on the plant selection and chose three herbs (basil, parsley and thyme) and three perennials (Nepeta cataria, rudbeckia and salvia). Like the annuals study, the herbs and perennials were grown in 4½-inch pots containing Fafard 3B bark-based growing mix without a fertilizer charge.

“In the case of basil, the initial application of organic fertilizer was enough to finish the crop,” Pasian said. “One single application incorporated into the growing mix before planting the plugs would be sufficient for the production cycle. For thyme it would be very close to finish with one application, almost the same as basil.”

Pasian is planning to repeat the trials with parsley because he encountered some issues with heat stress and disease problems.

“During the parsley trial even the control plants had problems,” he said. “The plants were grown during the summer so the warm temperatures in the greenhouse may have contributed to the problems. I expect when the parsley study is repeated during the winter and the temperatures have cooled down the results will be different.”

Pasian said since many perennials are long-term crops, they will need additional applications of organic fertilizers.

“In the perennial trials, the first flush of growth with the organic fertilizers was good,” he said. “But then the fertilizers ran out. Applying a powder or a small granular organic fertilizer to each pot is not realistic for growers. These organic fertilizers can be incorporated into the growing mix prior to planting. Once these fertilizers are used by the plants, which takes about five to six weeks, a grower can start applying a liquid organic fertilizer. This could be a fish emulsion or similar type fertilizer.

“One single organic fertilizer application incorporated into the growing mix is not enough. Additional fertilizer will need to be applied probably more than once. The plants grew decently with one application, but if larger plants are the goal then more fertilizer is going to be needed.”

Nepeta cataria (catnip) grew very fast initially and was the first perennial to show deficiency symptoms. Pasian said nepeta would require additional fertilizer applications sooner.

Rudbeckia took much longer to show any deficiencies. Pasian said since rudbeckia is a very slow crop with a longer production time, it will need supplemental fertilizer applications.

“Organically fertilized rudbeckia produced a first flush of growth that was as good as plants fed with water soluble and controlled-release fertilizers,” he said. “But as time went on during production, the organically fertilized plants needed another shot of fertilizer.

“I consider salvia to be an intermediate crop between catnip and rudbeckia. I expect that salvia will require additional fertilizer applications.”

Pasian will continue the trial with the same herbs and perennials this winter and coming spring. The plants will be grown in 1-gallon containers to match commercial production practices.

“This research is not being conducted with the goal of changing how fertilization is done by most growers,” Pasian said. “Water soluble fertilizers are excellent products that growers use successfully. This research will provide growers with information on how to produce a crop that has been fertilized in a more sustainable way to satisfy a small percent of their clients.

“Marketing is going to be the issue for growers. If they grow plants with both organic and water soluble fertilizers, those grown with the organic fertilizer are going to have to be marketed differently so the consumers know the difference and can make their choice about which plants to purchase.”

This article was written by David Kuack, a freelance technical writer in Fort Worth, Texas Email: [email protected]

For more information:
Hort Americas, LLC
Fort Worth Texas
1304 W. Euless Blvd #200
Euless, TX 76040
United States
Chris Higgings
Email: [email protected]
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