Micronutrient Disorders

By Dr. Claudio Pasian, Department of Horticulture and Crop Science

The Ohio State University

Micronutrient disorders are the fertility problems that I see most often while visiting growers as an Extension Specialist (Figure 1 and 2).  Micronutrients (from the Greek Micro=small and nutrient=nutritive) are mineral elements needed by plants in small quantities.  Small variations from the optimum level required for plant growth can be damaging.  By the same token, levels slightly above those required for good growth can be toxic.  It is very important for growers to have a clear understanding about micronutrient management.  This article is a brief overview of the principles that control the availability of micronutrients in soilless mixes and how to correct imbalances.

Figure 1. Typical iron deficiency symptoms on Streptocarpella. Please, note that the symptoms manifest on young leaves.

Figure 1. Typical iron deficiency symptoms on Streptocarpella. Please, note that the symptoms manifest on young leaves. Photo by Claudio Pasian.

Figure 2. Typical iron-manganese toxicity symptoms on Geranium. Photo by Claudio Pasian.

Figure 2. Typical iron-manganese toxicity symptoms on Geranium. Photo by Claudio Pasian.

Deficiency or Toxicity?  A micronutrient disorder may be a deficiency (when the micronutrient is in deficit) or a toxicity (when the micronutrient is in excess).  Deficiencies can occur either because the nutrients are not present in the growing mix or because the nutrient is present but unavailable to the plant.  (Occasionally, plants with roots damaged by Pythium or other pathogens may show micronutrient deficiency symptoms.)  Some commercially prepared mixes have a fertilizer charge that may include micronutrients.  Growers preparing their own mixes should use one of the many commercially available micronutrient complexes to ensure that the micronutrients are present in the growing mix.

Nutrient Availability.  Sometimes, the micronutrient present in a growing mix is not available to the plant (the plant cannot take it up).  Micronutrient availability is influenced by media pH: except for molybdenum, the availability of micronutrients decreases with increasing media pH and vice versa.  Water alkalinity is an important factor modifying media pH and hence micronutrient availability.  It is important to maintain the pH for soilless media between 5.5 and 6.3.  Some crops are more sensitive to media pH than others:  petunias and gerberas must be maintained at pH levels of 5.5 in order to avoid micronutrient deficiency symptoms.  Other crops are more tolerant of pH changes.  Table 1 shows the minimum and maximum critical foliar levels for floral crops.

Table 1.  General critical foliar ranges for floral crops.  (After J. Biernbaum, Water, growing media, fertilizer, and root zone management.  OFA Short Course, July 1994.)

Nutrient Minimum ppm Maximum ppm
Iron (Fe) 50 ?
Manganese (Mn) 30 500
Zinc (Zn) 20 100-200
Copper (Cu) 5 20-100
Boron (Bo) 25 100-300
Molybdenum (Mo) 0.5 15

Substrate pH.  If the deficiency is due to pH imbalance, the approach is to modify the pH of the mix.  In this case, adding micronutrients can make matters worse because the level of individual micronutrients may affect the level of other micronutrients in the plant through a process called antagonism.  For example, too much iron may produce manganese and zinc deficiencies, while high levels of manganese may result in iron and zinc deficiencies.  Copper and zinc are also antagonistic: too much of one may produce a deficiency of the other (Table 2).

Nutrient Toxicity.  Toxicity on the other hand, can occur when micronutrients are applied in excess (usually more than one application).  Common sources of micronutrients are: the charger in the mix and fertilizers applied during the crop cycle.  Growers MUST have an idea of how much micronutrient they are adding through each of these sources in order to avoid toxicities.  Toxicity symptoms are difficult to recognize visually (only someone with a lot of experience can do it) and are usually mistaken by deficiency symptoms by growers.

Correct Diagnosis.  How do we resolve these problems?  First of all, only a correct diagnosis of the problem will lead to the proper solution.  Do you have a micronutrient deficiency or is it an excess?  Identify the micronutrient causing the problem.  Identify the cause of the deficiency/toxicity: is the nutrient not present or is it present but unavailable? Answering these questions will help you (and your extension agent or consultant) tackle the problem.

Table 2.  Availability of micronutrients as affected by other micronutrients (antagonism) and macronutrients in soilless mixes.

Element Availability reduced by:
Boron Organic nitrogenous fertilizers and high levels of phosphorus.
Manganese High levels of potassium, phosphorus, iron, copper, zinc.
Copper High levels of zinc, nitrogen, and phosphorus
Iron High levels of copper, manganese, zinc, and phosphorus.
Molybdenum High levels of manganese and nitrate-nitrogen fertilizer.
Zinc High levels of copper and phosphorus.

How to Correct the Problem.  If deficiency or toxicity are suspected, soil and foliar analysis are recommended for several reasons.  First, visual identification of the problem is difficult in the absence of information (made available through analysis).  Second, damage may be occurring that is not yet visible and by the time it becomes visible, the damage may be irreversible.

Deficiencies can be corrected by adding the micronutrient that is in deficit or by correcting the factor that makes it unavailable (e.g. high pH).  This second course of action is very common among growers who have high alkalinity irrigation water.  If only one micronutrient is deficient, DO NOT apply a micronutrient complex fertilizer because, as we mentioned above, imbalances can cause antagonism.  Apply a salt that contains only the deficient micronutrient.

Micronutrients can be I) added over time in small amounts with the irrigation water (Table 3); II) applied once with a concentrated solution during a normal watering (Table 4); III) applied as a single foliar spray (Table 5).

Table 3.  Sources, rates, and micronutrient concentration for continuous soil application of one or more micronutrients with every liquid fertilization.    (After D.A. Bailey and P.V. Nelson, Managing micronutrients in the greenhouse.  NCSU Extension, Leaflet No 553, 1991.)

Micronutrient source

Weight of source per 100 gal (oz)

Concentration (ppm)
Iron sulfate–20% iron 0.13 2.00 Iron
Iron chelate (EDTA) — 12% iron 0.22 2.00 Iron
Manganese sulfate — 28% manganese 0.012 0.25 Manganese
Zinc sulfate — 36% zinc 0.0018 0.05 Zinc
Copper sulfate — 25% copper 0.0027 0.05 Copper
Borax — 11% boron 0.030 0.25 Boron
Sodium molybdate — 38% molybdemum 0.00035 0.01 Molybdemum
Ammonium molybdate — 54% molybdenum 0.00025 0.01 Molybdemum

Toxicities are not easily corrected.  The first step is stop adding the micronutrient that is in excess (switching to a fertilizer without the nutrient causing the problem).  Slightly changing (raising, for most Micronutrients) the media pH will decrease the availability of all micronutrients (including the one in excess).  Growers trying to correct a micronutrient excess should raise the pH at the maximum level that the species/cultivar can tolerate for normal growth.  Lastly, use antagonism as a tool: increase slightly the level of a micronutrient that will reduce the availability of another (e.g. if zinc is at high levels, slightly increase the level of copper).

Table 4.  Sources, rates and micronutrient concentrations for a single corrective application of one or more micronutrients applied to the soil*.  (After D.A. Bailey and P.V. Nelson, Managing micronutrients in the greenhouse.  NCSU Extension, Leaflet No 553, 1991.)

Micronutrient source

Weight of source per 100 gal (oz)

Concentration (ppm)
Iron sulfate–20% iron 4.0 62.0 Iron
Iron chelate (EDTA) — 12% iron 4.0 36.4 Iron
Manganese sulfate — 28% manganese 0.5 10.0 Manganese
Zinc sulfate — 36% zinc 0.5 13.9 Zinc
Copper sulfate — 25% copper 0.5 9.3 Copper
Borax — 11% boron 0.75 6.25 Boron
For soil-based media (>20% soil in media)
Sodium molybdate –38% molybdemum 0.027 0.77 Molybdemum
Ammonium molybdate — 54% molybdenum 0.019 0.77 Molybdemum
For soilless media
Sodium molybdate –38% molybdemum 2.7 77 Molybdemum
Ammonium molybdate — 54% molybdenum 1.9 77 Molybdemum

* Do not apply combinations without first testing on a small number of plants.  Wash solution off foliage after application.

Conclusion.  Micronutrient management is complex and difficult.  A more complete treatment of this subject would require more space than we have available here.  I hope, nevertheless, that my description of the problem piqued your curiosity.  At the very least, I hope that you follow this advice: Don’t guess. Test!

Following, is the contact information of some laboratories where you can send your samples for tissue analysis.  Additional labs for media, water, tissue and disease diagnosis can be found here: 2015 Analytical Laboratories for Greenhouse Nursery Fruit and Vegetable Producers. Consult with your local Extension Agent for a local plant testing laboratory.

Brookside Labs
308 S. Main Street
New Knoxville, OH 45871
419-753-2448

Calmar Lab
130 S. State Street
Westerville, OH 43081
614-523-1005

CLC Labs
325 Venture Dr.
Westerville, OH 43081
614-888-1663

NA-CHURS
421 Leather St.
Marion, OH 44654
800-344-1101
330-893-2933

Soil and Plant Nutrient Lab
Department of Crop and Soil Sciences
81 Plant & Soil Sciences Building
East Lansing, MI 48824-1325
515-355-0218

Soil Testing Laboratory
University of Kentucky
103 Regulatory Service Building
Alumni & Shawneetown Roads
Lexington, KY 40546-0275
606-257-7355

Spectrum Analytical Inc.
PO Box 639
Washington Court House, OH 43160
800-321-1562

Agricultural Analytical Services Laboratory
Penn State University
University park, PA 16802
814-863-4540

A & L Great Lakes lab
3505 Conestoga drive
Ft. Wayne, IN 46808
219-483-4759

Brookside Labs
308 S. Main Street
New Knoxville, OH 45871
419-753-2448

Calmar Lab
130 S. State Street
Westerville, OH 43081
614-523-1005

CLC Labs
325 Venture Dr.
Westerville, OH 43081
614-888-1663
This article lists lab references, but such reference should not be considered an endorsement or recommendation by the Ohio State University Extension, nor any agency, officer, or employee at the Ohio State University Extension. No judgement is made either for labs not listed in this article.

 

 

FIRM Welcomes USDA-ARS Scientist Dr. Jennifer Boldt

FIRM would like to welcome a new member to the team – Dr. Jennifer Boldt who officially joined the Greenhouse Production Research Group within the  USDA-ARS Application Technology Research Unit in Toledo, Ohio last October.  Jennifer holds B.S. and M.S. degrees from the University of Florida, and a Ph.D. in Applied Plant Sciences from the University of Minnesota. She  has over 20 years of commercial greenhouse production, garden trial management, and research experience – most recently in plant photosynthetic responses to light, temperature, and CO2, and the function and physiology of foliar anthocyanins. We are excited to have Jennifer and other members of the USDA-ARS team participate in FIRM meetings and events – and look forward to assisting the USDA-ARS in sharing their research efforts and results with the industry.  For additional information on research projects past and present, please visit the link to their website above.

Photo courtesy of USDA-ARS.  Back row, left to right: James Altland, Wendy Zellner, Charles Krause; Second  row: Madison Roze (student worker), James Locke, Adam Hall; Front row: Mona-Lisa Banks, Jennifer Boldt, Doug Sturtz, Sujin Kim

 

CONTROLLED-RELEASE FERTILIZERS in the PRODUCTION of CONTAINER-GROWN FLORICULTURE CROPS

Dr. Claudio Pasian

Floriculture Extension Specialist

Department of Horticulture and Crop Science

Columbus, OH 43210

In order for plant roots to absorb nutrients, the nutrients must be dissolved in the water surrounding the roots. The question is “How quickly does a fertilizer release these nutrients to the water surrounding the roots?”

Fertilizers differ in the rate at which their nutrients dissolve into water in the root zone. Water-soluble fertilizers (WSFs) dissolve more or less instantly; therefore, the nutrients they contain are available for uptake immediately after application (unless they are held by the solid phase of the rooting medium). Other fertilizers are manufactured to release nutrients more slowly. These so-called slow release fertilizers are typically coated with a resin or other substance which temporarily traps the nutrients within the fertilizer prill. The proper use of water-soluble and slow-release fertilizers is essential to achieving crop yield and quality, environmental stewardship, and profit goals.

Greenhouse and nursery production systems are intensively managed requiring high amounts of fertilizer for appropriate quality growth.  Nutrients are generally applied in the for WSFs.  However, because WSF can be easily leached, there is the potential of high nutrient losses.  Phosphates and nitrates are prone to leaching in greater quantities because they do not readily bind to negatively charged colloids.  As a consequence, they may appear in runoff. This problem may be compounded by the fact that most greenhouse and nursery growers do not capture or recycle leachate during production.

Slow-release-fertilizers (SRF) are designed to release nutrients slowly over time. Within the SRF category, we have the so called controlled-release-fertilizers (CRFs) that are fertilizers encapsulated inside a coat which slowly release nutrients over time.  This slow release increases the probability that nutrients will be taken by the roots.  This results in fewer loses (i.e. greater nutrient-use efficiency) and reduced pollution potential. This article covers only CRFs.

Controlled-release Fertilizer Design

Controlled-release fertilizers are also called coated or encapsulated fertilizers because the release is controlled by a polymer coating that contains a water-soluble fertilizer.  The first coatings were made of sulfur urea.  Due to cracks or uneven thickness of the coating, these materials produced irregular results.  Today’s coatings are made of resins allowing for better control of nutrient release.  These modern coatings are made of acrylic resins, polyethylene, waxes, and sulfur.  The two main families of common resins in use are the alkyd-type resins (e.g., Osmocote) and polyurethane-like coatings (e.g., Polyon, Plantacote, and Multicote).  The release of nutrients from the prills (the small spheres made of coated fertilizer) is controlled mainly by the thickness of the coating and the temperature.

 How Controlled Release Fertilizers Work

A semi-permeable coating surrounds a water-soluble fertilizer (Figure 2).  Water penetrates the coating and dissolves the fertilizer inside the prill increasing the osmotic pressure which in turn increases the size of the coat’s micro-pores.  The fertilizer solution then exits the prill through the coating pores into the substrate.  In addition to temperature, the release will depend also on the type and thickness of the coating, the salt composition, and the salt concentration differential between the inside and outside of the prill.  However, the two most important factors are coating thickness and temperature.

Current Use of and Barriers to further Adoption of Controlled-Release Fertilizer

CRFs are not widely used in containerized greenhouse floriculture production except for stock plants, poinsettias, hanging baskets, and garden mums. Even in these few exceptions, CRFs are used as a supplement to water-soluble fertilizers. One reason for limited use of CRFs in floriculture production could be the inadequate knowledge regarding their use for herbaceous plant production. Other reasons include fear for possible plant damage due to salt accumulation when applied at higher rates. Some growers may also fear the loss of control over their fertigation program and thus feel they are unable to employ techniques such as ‘toning’ crops to meet production goals. Toning is the alteration of fertigation practices at the end of the production cycle to improve post-production quality after plants leave the greenhouse.

At The Ohio State University, we have grown numerous bedding and container floriculture crops and some herbs with a single (initial) application of controlled release fertilizers (Figure 1).  In most cases, CRF-produced plants were equal — if not higher – in quality to plants grown with water-soluble fertilizers.

 Why Use Controlled Release Fertilizers?

CRF use has three main advantages.  First, it may simplify nutrient management relative to repeated applications of WSFs. Second, CRF use can increase nutrient use efficiency. Third, CRF use can enhance crop performance.


CRFs supply nutrients for a relatively long period of time and, for some greenhouse crops, for the entire production cycle.  After applying fertilizer prills to the mix before planting, no water-soluble fertilizer equipment is need and irrigation is done with tap water only.  Fewer nutrients are lost in the leachates because nutrients are slowly released throughout the season and remain present in the substrate at the time when the plants have developed roots to absorb them.  CRFs have the potential of increasing fertilizer efficiency (nutrient absorbed / nutrient applied) and reducing nutrient losses into the environment.

There is evidence that some plants grown with CRF perform better in the landscape than plants grown with water-soluble-fertilizer.  This effect carries over to the landscape assuming that not a lot of time has passed between when the plant is ready to sell and the time it is planted in the landscape.

Fertilizer Longevity

Longevity of a CRF refers to the time it takes for all nutrients to leave the prills at a given temperature.  This temperature is usually 70˚F (some companies may use 82˚F).  The thickness of the coating determines the longevity. The thicker the coating, the slower the prills release nutrients.

Always check on the fertilizer bag for the temperature that was used to determine longevity.  If the temperature of the substrate where the prills are located is higher than that specified on the bag, the release will be faster than specified. At lower temperatures, it will be slower.  The most common longevities are: 3 – 4 months, 5 – 6 months, 8 – 9 months, and 12 – 14 months.  In summary, increased longevities are the results of thicker coatings.

Growers should be aware that adjusting the CRF rates of application is necessary when using different longevities.  In order to achieve maximum plant growth, CRF of extended longevities require higher application rates.

At low application rates, greater longevity CRFs (e.g. 8-9 month or 12-14 month) release insufficient nutrients to meet the demands of rapidly growing crops early in the season.  At higher application rates, release by shorter longevity CRFs (e.g. 3-4 month) may result in excessively high salt levels (high electrical conductivity [EC]) and poor growth.   At low fertilizer application rates, the faster release rate (shorter longevities) CRFs can produce larger plants. At higher application rates, slower release CRFs (longer longevities) can outperform the faster release CRFs (Figure 3).

 Prill Cracking

The coating material of the prill can have cracks if the CRF is mishandled and damaged.  Through these cracks, the fertilizer can be released very fast defeating the purpose of using a CRF.  The bags with CRF should be handled gently.  Care should also be taken when mixers and pot fillers are used to avoid prill breakage by the growing mix handling equipment.

 Application Methods

Growers can apply CRFs to container-grown plants in different ways: 1) top-dresses; 2) “dibble planting”; 3) incorporated into the media; and 4) layered.  When top-dressed, the prills are deposited on the top of the substrate in the container.  For large number of containers, a dispenser is essential to do an efficient job (faster and fewer loss of prills).  Dibble planting consists in making a hole in the substrate and adding a pre-measured amount of CRF before planting the plug or liner in the container. 

Uniformity of Prill Distribution

In order to achieve the appropriate dose, the right amount of prills (number or weight) should reach each container.  This can be difficult to achieve when small containers are used (cell packs or plug trays).  For these containers, it is recommended to use CRFs with prills of smaller diameter that facilitate uniform distribution in the substrate.  An alternative for small containers is to apply both CRF and water-soluble fertilizers.

 Irrigation

Do not over irrigate when using CRFs!  Excess watering can lead to leaching of nutrients.  It is better to irrigate often with small volumes than only once for a long period of time.  Efficient irrigation can be achieved by programmable timers, computerized irrigation, sensors, or a combination of these.

 CRFs and Substrate pH and EC

Research has shown that with CRFs there is less substrate pH drift than with WSFs. As a consequence, growers who use acidic fertilizers to compensate for high alkalinity levels in the irrigation water need to adjust the amount of acid added.  On the other hand, the effect of CRFs on substrate EC is small and results in lower substrate EC levels.  Growers who monitor substrate EC of their crops, should keep in mind that they will measure lower (but still acceptable EC levels) than when WSF are used.  

 Storage

All fertilizers should be stored indoors on a concrete pad with a curb that will contain spills or leaks. CRFs should be stored in a dry environment, especially if the plastic bags have been opened.  It is also important to minimize the movement of these bags and when necessary, they should be handled with care to avoid cracking the prills.  Cracks in the prills will release nutrients faster than specified in the label.  When CRFs are blended into the growing mixes before use, these mixes should not be stored. The mixes should be used as soon as possible to avoid water absorption by the prills and possible nutrient losses before planting. 

 How to start using CRFs

It is a good idea, for growers who have limited experience with CRFs, to start small.  Selecting a crop or a portion of a crop, and becoming familiar with the new cultural practice would be prudent.  After that, slowly expanding to more crops/areas will be prudent.  Always start with the lowest rate listed in the label for a given crop and container size.  If more fertility is needed, apply WSF.  Keeping records of what is done and when it is done will help growers master the use of CRFs.

 Always read the label and consult your fertilizer sales representative or your Extension Educator if you have any doubts. 

Disclaimer:  This article may contain fertilizer recommendations that are subject to change at any time.  These recommendations are provided as a guide.  It is always the applicator’s responsibility to read and follow all current label directions for the specific fertilizer being used. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned.  The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.

Figure 1.  Salvia plants grown in 4.5 inch diameter plastic containers using a 20-10-20 water-soluble fertilizer at an application rate of 150 ppm N (left), or a 16-9-12 controlled release fertilizer of 5-6 month longevity  (center), or  8-9 month longevity (right) at a rate of 5 grams (0.18 oz)  per container.  Marketable plants were produced with all three fertilizers. (Photo by C. Pasian)

Figure 1. Salvia plants grown in 4.5 inch diameter plastic containers using a 20-10-20 water-soluble fertilizer at an application rate of 150 ppm N (left), or a 16-9-12 controlled release fertilizer of 5-6 month longevity (center), or 8-9 month longevity (right) at a rate of 5 grams (0.18 oz) per container. Marketable plants were produced with all three fertilizers. (Photo by C. Pasian)

 

Figure 2.  Representation of a CRF prill absorbing water and then releasing the fertilizer solution.  The rate of release will depend, among other things, on the salt differential between the interior and exterior of the prill.  Initially, the concentration of salts inside the prill is very high (represented by the word salts between brackets).  Outside the prill, the salt concentration is lower.  Such salts’ gradient favors the release of nutrient from the prill’s micro-pores.

Figure 2. Representation of a CRF prill absorbing water and then releasing the fertilizer solution. The rate of release will depend, among other things, on the salt differential between the interior and exterior of the prill. Initially, the concentration of salts inside the prill is very high (represented by the word salts between brackets). Outside the prill, the salt concentration is lower. Such salts’ gradient favors the release of nutrient from the prill’s micro-pores.

Figure 3.  Shoot dry weight of Impatiens wallerana plants (common impatiens) as a function of a 15-9-12 controlled release fertilizer concentration of four different longevities: 3-4, 5-6, 8-9, and 12-14 months. Note how the maximum shoot dry weight (peak) of each fertilizer curve moves slightly towards higher concentrations (towards the right) with increasing longevities. (After G.A. Andiru, C.C. Pasian, J. M. Frantz, and P. Jourdan (2013). “Longevity of Controlled-Release Fertilizer Influences the Growth of Bedding Impatiens.”)

Figure 3. Shoot dry weight of Impatiens wallerana plants (common impatiens) as a function of a 15-9-12 controlled release fertilizer concentration of four different longevities: 3-4, 5-6, 8-9, and 12-14 months. Note how the maximum shoot dry weight (peak) of each fertilizer curve moves slightly towards higher concentrations (towards the right) with increasing longevities. (After G.A. Andiru, C.C. Pasian, J. M. Frantz, and P. Jourdan (2013). “Longevity of Controlled-Release Fertilizer Influences the Growth of Bedding Impatiens.”)

SUSTAINABLE FERTILIZERS FOR CONTAINERIZED FLORICULTURE CROPS

Some definitions

Organic, inorganic, natural, artificial. . . These and similar, popular terms like chemical, mineral, synthetic, sustainable, etc. can be confusing due to the use of many undefined words or words with dubious meaning.

Chemically speaking, organic compounds include the carbon atom in their chemical composition regardless of their source. Inorganic chemicals, then, are those without carbon. For example, propane gas is an organic compound because its molecule is composed of three atoms of carbon and eight atoms of hydrogen.

Are “organic fertilizers” those that contain carbon? Not necessarily. Things have become more complicated than that. Years ago, the term “organic” meant that something was pesticide free but government regulation has created a whole new bureaucratic vocabulary. For example, limestone, mined rock phosphate, and Chilean saltpeter are inorganic chemicals whose use government regulation permits in organic agriculture.

Sustainable Fertilizers

For the purpose of this Fact Sheet, we will use the term sustainable fertilizer to describe those derived from animal and plant byproducts such as manures, blood, bones, compost, cottonseed meal, etc., produced in manufacturing and farming (Table 1).

Table 1.  Non-branded materials that can be used as sustainable fertilizers and their estimated analysis (N-P-K).  Nutrient levels are approximate because they can change from batch to batch and from year to year.

Of Plant Origin

Of Animal Origin

Alfalfa meal  2-1-2

Bat guano  10-3-1

Corn Gluten meal

Blood meal  12-1-0.5

Cotton seed meal  6-0.5-1.5

Bone meal  3-15-0

Dried manure  variable

Crab meal  10-05-01

Kelp powder  1-0.5-8

Feather meal  12-0-0

Soybean meal  9-0-0

Fish emulsion  5-2-2

 

Fish meal  10-5-1

 

Guano  12-11-2.5

 

Worm castings  1.5-2.5-1.3

All these materials are chemically organic regardless of being approved by federal government’s Organic Materials Review Institute (OMRI at www.omri.org). Fertilizers derived from animal and plant byproducts are only minimally processed and their nutrients remain in their natural forms as opposed to being industrially separated and purified.

Sustainable vs. Organic Growing

It has been shown that individuals interested in buying products that have been grown in a sustainable way comprise a substantial portion of the ornamental market. Furthermore, these customers are even willing to pay slightly more for these products. Greenhouse growers do not have to be “organic growers” to use sustainable fertilizers. Growers can simply replace the water soluble mineral fertilizers (e.g. 20-10-20) of a portion of their crops with sustainable fertilizers and still continue with their traditional cultural practices. It is important, however, to let consumers know which plants were grown with what fertilizer in order for them to choose. It is also good marketing to let consumers know when crops involve sustainable practices and materials.
Nutrient Ratios

Sustainable fertilizers tend to have smaller nutrient ratios. Examples of sustainable fertilizers are: Sustane 8-4-4, Scotts Miracle-Gro Organic Choice Plant Food 7-1-2, and Daniels 10-4-3. A list of commercially available sustainable fertilizers can be seen in Table 2. On the other hand, ratios of mineral fertilizers tend to be larger, such as the case of one the most-used fertilizers in greenhouse containerized floriculture: Peters 20-10-20 water-soluble fertilizer.

How do sustainable fertilizers work?

Sustainable fertilizers sold under a brand are, most likely, the result of a high quality compost process. When applied to substrates, these products are degraded by micro-organisms making the nutrients available to plants. As a consequence, these fertilizers can be classified as slow release fertilizers because they supply nutrients in small quantities over a longer period of time. Companies producing and selling sustainable fertilizers should provide information about their longevity (the time it takes for all nutrients, at a given temperature, to be totally released). Unfortunately, longevity of sustainable fertilizers is not always provided. Anecdotal information indicates that longevity of sustainable fertilizers is shorter than for controlled-release fertilizers.

Factors, like temperature and water availability, influence microbial activity that in turn will influence nutrient availability. In fact, temperature and water availability are crucial: soils that are too dry or too wet, to cold or too hot will reduce microbial activity and hence nutrient availability. Some of the products used to produce sustainable fertilizers may increase the substrate salt levels above acceptable levels making electrical conductivity (EC) monitoring very important.

Numerous brands of sustainable fertilizers can be found on the market. Each fertilizer responds differently than the water soluble fertilizers used in the greenhouse industry. As a consequence, there are no clear standards for managing nutrition when using sustainable fertilizers on soilless growing mixes.

Table 2. Some examples of commercially available sustainable fertilizers, their analyses, and material sources used in their production. Some of them may only be sold at retail stores for the home gardeners.

  Brand

Analysis

Source Material

Bradfield Organics All Purpose

5-5-5

Meat meal, alfalfa, potash, molasses, soft rock phosphate, fish meal, blood meal

Daniels

10-4-3

Organic base of soybean extract that is fortified with NPK and micronutrients

Earthworks

5-4-5

Caged layer manure

Espoma Garden Tone

3-4-4

Hydrolyzed Feather Meal, Pasteurized Poultry Manure, Cocoa Meal, Bone Meal, Alfalfa meal, green sand, humates, Sulfate of Potash, and Sulfate of Potash Magnesia

Miracle Gro Organic Choice All Purpose

7-1-2

Pasteurized pelleted poultry litter and feather meal.

Miracle Gro Organic Choice Steamed Bone-meal

6-9-0

Bone Meal

Organica Plant Booster

8-2-4

Feather Meal, Steamed Bone Meal and sulfate of potash

Pearl Valley

4-3-2

Composted caged layer manure

Perdue Agricycle w/ masking agent

4-3-3

Broiler litter crumbled pellets

Sustane 4-6-4

4-6-4

Aerobically composted turkey litter, hydrolyzed feather meal and sulfate of potash

Sustane 8-4-4

8-4-4

Aerobically composted turkey litter, hydrolyzed feather meal and sulfate of potash

Mode of application

Most sustainable fertilizers are dry and are applied as powders or small granules to the growing mixes either before or after planting. Other fertilizers are applied as liquids (e.g. Daniels) or liquid emulsions (fish emulsion). Liquid fertilizers can be applied using injectors making multiple applications during the life of the crop possible.

Variability

There is the potential for variability between batches of the products used to make sustainable fertilizers (Table 1) because many of them are derived primarily from waste materials. Only companies selling consistent products will be successful because greenhouse growers expect consistent sustainable fertilizers.

Storage

Bio-reactions can occur during the storage of these materials. Sustainable fertilizers with high carbon-to-nitrogen ratios and adequate microbiology in the presence of moisture could begin to decompose. Should decomposition occur, the macro-nutrient content as well as other key attributes of the organic fertilizer could become altered. Sustainable fertilizers should be stored in a dry environment and in containers that protect the fertilizers from the vermin that can feed on these materials.

How to Start Using Sustainable Fertilizers

It is a good idea, for growers who have limited experience with sustainable fertilizers, to start small. Selecting a crop or a portion of a crop, and becoming familiar with the new cultural practice would be prudent. After that, slowly expand to more crops/areas.

Always read the label of the product and consult your fertilizer sales representative or your Extension Educator if you have any doubts.

At The Ohio State University, we have grown numerous bedding and container floriculture crops and some herbs with a single (initial) application of sustainable fertilizers (Figures 1-4). We were able to show that these fertilizers can be used to produce quality crops. In some cases, with sustainable fertilizers, the plants were slightly smaller but still marketable. Under certain circumstances, smaller plants may be desirable to avoid the application of plant growth regulators.

Figure 1.  Petunia plants grown with Miracle Gro Organic Choice All Purpose 7-1-2 at a rate of 5.9 grams per pot (left), Sustane 8-2-4 at a rate of 5.1 grams per pot (center) and Osmocote 15-9-12 at a rate of 2.7 grams per pot (right).  Top = side view; Bottom = top view.

Figure 1. Petunia plants grown with Miracle Gro Organic Choice All Purpose 7-1-2 at a rate of 5.9 grams per pot (left), Sustane 8-2-4 at a rate of 5.1 grams per pot (center) and Osmocote 15-9-12 at a rate of 2.7 grams per pot (right). Top = side view; Bottom = top view.

 

Figure 2.  Seed geranium plants grown with a water soluble fertilizer Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed (left) or with a single application of Sustane 8-4-4 of 2.6 grams per 4.5 inch container (right).

Figure 2. Seed geranium plants grown with a water soluble fertilizer Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed (left) or with a single application of Sustane 8-4-4 of 2.6 grams per 4.5 inch container (right).

 

Figure 3.  Basil plants grown with a water soluble fertilizer solution of a Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed (left) and three rates of Miracle Gro Organic Choice (from left to right): 5.9, 4.5, or 3 grams per 4.5 inch container.

Figure 3. Basil plants grown with a water soluble fertilizer solution of a Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed (left) and three rates of Miracle Gro Organic Choice (from left to right): 5.9, 4.5, or 3 grams per 4.5 inch container.

Figure 4.  New Guinea impatient plants grown with (from left to right): water soluble fertilizer  Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed; Osmocote 15-9-12 at a rate of 3.2 grams per pot; and three rates of Miracle Gro Organic Choice (from left to right): 2.2, 3.0, or 5.9 grams per 4.5 inch container.

Figure 4. New Guinea impatient plants grown with (from left to right): water soluble fertilizer Peters 20-10-20 at a rate of 100 ppm N applied with irrigation as needed; Osmocote 15-9-12 at a rate of 3.2 grams per pot; and three rates of Miracle Gro Organic Choice (from left to right): 2.2, 3.0, or 5.9 grams per 4.5 inch container.


Dr. Claudio Pasian
Floriculture Extension Specialist
Department of Horticulture and Crop Science
Columbus, OH 43210