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Publication #ABE 373

Organic Greenhouse Container Herb Production in South Florida: Fertilizer and Potting Media1

D. D. Treadwell, Kati W. Migliaccio, Teresa Olczyk, Yun Qian, Y. Li, George J. Hochmuth, Robert C. Hochmuth, Eric H. Simonne, Lance S. Osborne, and Richard K. Sprenkel2

Background

Organic food production in the U.S. increased approximately 20% annually during the past 15 years. Organic herb sales continue to increase as consumer interest in organic food grows. Public interest in organic foods has grown since the implementation of national organic standards by the U.S. Departement of Agriculture (Greene and Dimitri, 2003).

Field production of organic crops, including herbs, in south Florida is a challenging task due to the subtropical climate and high number of pest and disease pressures. Thus, greenhouse production of organic herbs may provide an alernate to field production. However, there is little published information on selecting media and fertilizers for organic herb production in greenhouses in this climate.

Objectives

Greenhouse trials were conducted during the 2005 and 2006 growing season at the University of Florida IFAS Tropical Research and Education Center (TREC) in Homestead, Florida. The objectives of the project were to 1) compare several commercially available organic fertilizers for organic greenhouse production of container herbs and 2) compare two commercially available potting media for organic greenhouse production of container herbs.

Methods

The three commercial certified organic fertilizers used in this project were Nature Safe (Griffin Industries, 8-5-5; Coldspring, KY), Fertrell (Fertrell Company, 4-2-4; Bainbridge, PA), and Perdue (Perdue Agri Recycle, 4-2-3; Seaford, Delaware). They were compared with a control treatment of no fertilizer application.

Two certified organic potting media were used. These were Fafard Organic formula (Conrad Farfard, Inc.; Agawam, MA) and Agro-Soils commercial potting medium (Agro Soils; Miami, FL).

The three organic fertilizers were mixed with the two potting media at specified rates (Fafard and Agro-Soils, Table 1). The different rates were due to the nutrient composition of each fertilizer. Table 1 also includes the cost per 50 lb bag of each fertilizer.

The Control treatment consisted of 0 grams of fertilizer per gallon of potting medium. Potting mixes were placed in 4 inch diameter plastic pots. The four treatments (Nature Safe fertilizer, Fertrell fertilizer, Perdue fertilizer, and Control (no fertilizer)) were replicated four times and each replication consisted of six pots.

Pots were seeded with basil (Ocimum basilicum) (Fig. 1) and dill (Anethum graveolens) (Fig. 2). A light pinch of seeds (about 280 mg seeds for basil and 170 mg seeds for dill) was placed in each pot on the top of the potting mix and covered with ~5 mm of potting mix.

Basil is available in many different types and has a pleasant aroma. Basil has green, tender broad leaves that may be used fresh or dried. Basil is well known for its culinary use; however, it is also a versatile landscape plant (Wetherbee, 2001). Dill is a flavoring plant (i.e., dill pickles) with a strong-aroma and fennel-like structure (Stephens, 1998).Dill has also been used to sooth digestion and hiccups.

Figure 1. 

Basil showing its light green, silky broad leaves.


Credit:

UF/IFAS: Yun Qian


[Click thumbnail to enlarge.]

Figure 2. 

Dill showing its finely divided thread-like leaves.


Credit:

UF/IFAS: Yun Qian


[Click thumbnail to enlarge.]

Pots were placed in a greenhouse and irrigated with time-controlled overhead sprinklers. Plants were grown to obtain a marketable product to be sold as organic potted herbs. Irrigation was adjusted during the course of the experiment to ensure this goal.

Each of the two trials lasted approximately four weeks. The quality of plants at the end of four weeks was evaluated using several different criteria, including visual quality, fresh weight and dry weight of above ground plant tissue, percent of total nitrogen (TN) and total carbon (TC) from plant tissue, nitrate (NO3-N) and potassium (K+) concentrations in plant sap, and pH and electric conductivity (EC) in leachate.

Leachate sampling for pH and EC was conducted as an indicator of nutrient loss from the potting mix by leachate.

Data were evaluated with analysis of variance and Duncan's multiple range test using PROC GLM program in SAS 9.1.2 to evaluate differences in mean values among fertilizer and potting media treatments. Statistics were completed for each trial separately.

Results and Discussion

Evaluation of results indicated that there were no significant differences between the two potting media for all measured parameters. Thus, the data were analyzed by fertilizer type only. Results are presented in Tables 2, 3, 4, and 5. The 'a', 'b', and 'c' values in each table represent statistical results such that values with common letters are not significantly different and values with uncommon letters are significantly different.

The visual inspection, fresh weight, and dry weight measurements for basil and dill indicated that Perdue and Fertrell fertilizers provided the most visually pleasing and largest plants (Table 2 and Table 3).

Plant tissue nutrient results differed by herb (Table 4 and Table 5). Nutrient composition for basil was highly variable. Basil plants from the control fertilizer treatment had the greatest concentration of NO3-N for both trials. However, %TN was the lowest in the control treatment for both trials. Percent TN was significantly greater in the Nature Safe basil treatment than other fertilizer treatments. The lack of correlation between NO3-N and %TN was likely due to the different nature of the tests. For NO3-N, plant sap was measured from several leaves. Alternatively, %TN was measured using dried biomass of a larger sample of the plant. Another possibility is the very nature of the nitrogen form. Percent TN includes both organic and inorganic forms of nitrogen, whereas NO3-N only considers the inorganic form of nitrogen.

Percent TC for basil treatments varied by trial. There were no signficiant differences in the first trial, and %TC was significantly greater in Natural Safe and the Control fertilizer treatments in the second trial.

For dill, NO3-N results were inconclusive with Fertrell having the greatest concentration in the first trial and Natural Safe and Perdue having the greatest concentrations in the second trial. Similarly, K+ results did not consistently identify one fertilizer as resulting in the greatest concentrations for dill. TN and TC percentages in dill also varied by trial; however the Natural Safe fertilizer treatment was consistently high.

Hence, plant tissue and plant sap nutrient results did not clearly identify a fertilizer treatment that was significantly better than another.

Results from pH testing of leachate offered little additional information with minimal significant variation among treatments. Similarly, there were no significant differences among any treatments when evaluating leachate EC.

Conclusions

The two potting media (Fafard and Agro-Soils) did not result in significant differences in measured plant mass production, plant tissue nutrients, or leachate chemistry. However, some differences in plant production for basil and dill were identified among the different fertilizer treatments (Natural Safe, Perdue, Fertrell, and Control). These differences were most notable for visual quality, fresh weight, and dry weight measurements. Evaluation of these parameters for basil and dill suggested that the two best fertilizers were Perdue and Fertrell. However, the differences in cost of each fertilizer and the study results suggest that Perdue is a more economic choice for organic herb production of basil and dill.

Results of these two trials for growing organic herbs in south Florida suggest that (1) there is no difference in using Fafard or Agro-Soils potting medium and (2) Perdue and Fertrell fertilizers resulted in greatest plant mass production.

Clearly appropriate potting media and fertilizer formulations are commercially available for use in greenhouse production of basil and dill.

Reference

Greene, C. and C. Dimitri. 2003. Organic agriculture: gaining ground. Amber Waves 1(1):9.

Stephens, J. M. 1998. Herbs in the Florida Garden. This document is CIR570, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. http://edis.ifas.ufl.edu/VH020

Wetherbee, K. 2001. A bounty of fresh basil - herb gardening tips. Flower & Garden Magazine. May, 2001.

Tables

Table 1. 

Potting mix rates of fertilizer and potting media

Fertilzer

Composition

Grams of fertilizer per gallon of potting media

Cost per 50 lb bag

Nature Safe

Feather, meat, bone and blood meals, sulfate of potash, yeast, sugars, carbohydrates, and humus

40

$16.50

Fertrell

Aragonite, bone char, composted chicken manure, sodium nitrate, feather meal, greensand, peanut meal, sulfur, sulfate of potash

80

$16.13

Perdue

Poultry litter

80

$8.75

Table 2. 

Data collected for trial 1. Means with same letter are not significantly different by Duncan's multiple range test (p=0.05)

Crop

Fertilizer

Visual

Fresh weight (g)

Dry weight (g)

pH (standard units)

EC (uS/cm)

Dill

Natural Safe

2.03b

12.05b

2.08b

7.07ba

1592ba

Dill

Perdue

4.25a

61.80a

5.41a

6.66b

1493ba

Dill

Fertrell

4.47a

59.31a

5.29a

6.72a

3570a

Dill

Control

1.00c

5.53b

0.69b

7.29a

525b

Basil

Natural Safe

2.75b

79.50b

4.78b

6.77b

1643a

Basil

Perdue

4.56a

135.74a

9.03a

6.96ba

450a

Basil

Fertrell

4.81a

131.60a

9.46a

6.90ba

1772a

Basil

Control

1.00c

12.59c

1.64c

7.37a

392a

Table 3. 

Data collected for trial 2. Means with same letter are not significantly different by Duncan's multiple range test (p=0.05)

Crop

Fertilizer

Visual

Fresh weight (g)

Dry weight (g)

pH (standard units)

EC (uS/cm)

Dill

Natural Safe

1.19b

5.28b

0.13b

7.13ba

432a

Dill

Perdue

2.25a

14.11a

0.58a

7.05b

472a

Dill

Fertrell

2.38a

13.66a

0.56a

7.14ba

460a

Dill

Control

1.00b

4.31b

0.19b

7.21a

414a

Basil

Natural Safe

3.19b

51.78b

2.84b

7.05a

357a

Basil

Perdue

4.25a

89.88a

4.84a

7.07a

382a

Basil

Fertrell

4.31a

83.49a

4.79a

7.18a

373a

Basil

Control

1.00c

11.74c

0.66c

7.20a

396a

Table 4. 

Nutrient data collected for trial 1. Means with same letter are not significantly different by Duncan's multiple range test (p=0.05)

Crop

Fertilizer

NO3-N (mg/L)

K (mg/L)

%TN

%TC

Dill

Natural Safe

1095b

1197cb

4.0a

35.3a

Dill

Perdue

682b

2167a

2.7b

34.6ba

Dill

Fertrell

5047a

1643b

4.2a

34.0b

Dill

Control

832b

843c

1.0c

34.0b

Basil

Natural Safe

1162b

682a

4.0a

36.5a

Basil

Perdue

402b

805a

2.5c

37.1a

Basil

Fertrell

918b

588a

3.1b

37.1a

Basil

Control

4645a

345a

1.0d

37.1a

Table 5. 

Nutrient data collected with statistical indicators for trial 2

Crop

Fertilizer

NO3-N (mg/L)

K (mg/L)

%TN

%TC

Dill

Natural Safe

653ba

1547a

3.2a

33.4a

Dill

Perdue

762a

1577a

2.8ba

32.3b

Dill

Fertrell

345bc

1007a

2.5b

33.2a

Dill

Control

313c

1295a

1.3c

33.6a

Basil

Natural Safe

413a

235b

3.0a

35.7ba

Basil

Perdue

405a

493a

2.1b

34.8c

Basil

Fertrell

248a

410a

2.0b

35.3b

Basil

Control

452a

457a

1.2c

36.1a

Footnotes

1.

This document is ABE 373, from the Department of Agricultural and Biological Engineering, UF/IFAS Extension. First Published: May 2007. Reviewd July 2010 and October 2013. Please visit the EDIS website at http://edis.ifas.ufl.edu.

2.

D. D. Treadwell, assistant professor, organic and sustainable vegetable production, Department of Horticultural Sciences, Gainesville, FL; Kati W. Migliaccio, Extension specialist, Tropical Research and Education Center (TREC), Homestead, FL; Teresa Olczyk, county Extension director, commercial agriculture/vegetables, UF/IFAS Extension Miami-Dade County; Yun Qian, former post-doctoral research associate, TREC, Homestead, FL; Y. Li, Extension specialist, TREC, Homestead, FL; George Hochmuth, professor, Department of Soil and Water Science, Gainesville, FL; Robert C. Hochmuth, multicounty Extension agent, vegetables, Live Oak, FL; Eric H. Simonne, associate professor and northeast district Extension director, Gainesville, FL; Lance S. Osborne, professor, Mid-Florida Research and Education Center, Apopka, FL; Richard K. Sprenkel, Extension specialist (retired), North Florida Research and Education Center, Quincy, FL.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication does not signify our approval to the exclusion of other products of suitable composition. All chemicals should be used in accordance with directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.