Iron chelate for plants

Chelated Iron Uses: Learn How To Use Chelated Iron In Gardens

When reading the labels on fertilizer packages, you may have come across the term “chelated iron” and wondered what it is. As gardeners, we know that plants require nitrogen, phosphorus, potassium and micronutrients, such as iron and magnesium, to grow properly and produce healthy blooms or fruit. But iron is just iron, isn’t it? So exactly what is chelated iron? Continue reading for that answer, and tips on when and how to use chelated iron.

What is Chelated Iron?

Symptoms of iron deficiency in plants can include chlorotic foliage, stunted or malformed new growth and leaf, bud or fruit drop. Usually, symptoms do not progress more than just discoloration of the foliage. Iron deficient leaves will be green veined with a mottled yellow color in the plant tissues between the veins. Foliage may also develop brown leaf margins. If you have foliage that looks like this, you should give the plant some iron.

Some plants can be more prone to iron deficiencies. Certain soil types, such as clay, chalky, overly irrigated soil or soils with high pH, can cause available iron to become locked up or unavailable to plants.

Iron is a metal ion that can react to oxygen and hydroxide. When this happens, the iron is useless to plants, as they are not able to absorb it in this form. To make iron readily available for plants, a chelator is used to protect the iron from oxidation, prevent it from leaching out of the soil and keep the iron in a form that the plants can use.

How and When to Apply Iron Chelates

Chelators may also be called ferric chelators. They are small molecules that bind to metal ions to make micronutrients, such as iron, more readily available to plants. The word “chelate” comes from the Latin word “chele,” which means lobster claw. The chelator molecules wrap around metal ions like a tightly closed claw.

Applying iron without a chelator can be a waste of time and money because the plants may not be able to take up enough iron before it becomes oxidized or leached from the soil. Fe-DTPA, Fe-EDDHA, Fe-EDTA, Fe-EDDHMA and Fe-HEDTA are all common types of chelated iron that you may find listed on fertilizer labels.

Chelated iron fertilizers are available in spikes, pellets, granules or powders. The latter two forms can be used as water-soluble fertilizers or foliar sprays. Spikes, slow-release granules and water-soluble fertilizers should be applied along the plant’s drip line to be most efficient. Foliar chelated iron sprays should not be sprayed on plants on hot, sunny days.

COURTESY Ornamental plums, also called purple leaf plums, are actually fruit-bearing trees that are sold for ornamental landscapes because of their showy flowers.iron chlorosis

Q: I was told I need chelated iron for my roses. So, per instructions, I added the granulated type today. My question is, how often do I do this? They do not mention this on the label, just the dosage.

A: Chelated iron means the iron is “captured” by a chemical, called a chelate, that protects it. As long as the iron is protected, it can be used by the plant. Once the iron is “let go,” it is no longer protected. In our soils and water, if left unprotected, the iron can no longer be used by the plant.

You must have mentioned that your rose bushes were yellowing to get this kind of advice. If the person helping you is knowledgeable, they would ask if the yellow leaves were on the ends of branches (new leaves) or further inside the plant on older leaves. If this is an iron problem, the yellowing would be on the newer leaves. If yellowing is on older leaves, it is a different problem.

There are two methods of correcting yellow leaves suffering from iron problems. One method is to apply chelated iron to the soil. The other method that is to spray chelated iron, mixed with water, on the leaves.

Timing, or when to apply the chelated iron, is critical depending on the method. Chelated iron must be applied to soils in the very early spring before or as new growth is emerging.

Applying chelated iron to the soil is the most effective way of correcting plants with yellow leaves because it only requires a single application.

The most effective chelated iron to apply to soils contains the chelate EDDHA in the ingredients. The more EDDHA iron on the label, the more effective it is.

At this time of year, or any time after early spring, chelated iron must be sprayed on the leaves to be effective. Applying it to the soil will not work.

Unlike soil applications, which are required only once in the spring, spraying iron on the leaves requires multiple applications for most trees and shrubs. Applications to the leaves may be required four or five times, a few days apart, to get a decent green color again.

The label may not tell you so, but always use distilled or reverse osmosis water when mixing chelated iron to make a foliar spray. Our water is very alkaline, which reduces the effectiveness of the iron chelate.

Also, use 1 teaspoon per quart of a mild liquid detergent such as Castile soap mixed into the solution as the last ingredient. Liquid detergents help move the chelated iron through the waxy leaf surface and inside the plant.

Q: I cannot find the white or yellow honeysuckle here that grew in West Texas and smells so wonderful. Perhaps you can tell me why in Odessa, Texas, fruitless plum trees are actually fruitless and don’t fall easy prey to borers.

A: The primary reason you can’t find familiar plants here is because of marketing and sales of local nurseries and gardens centers. The temperatures and soils are similar enough between West Texas and Southern Nevada, so many plants grown there would work here.

You also have Texas A&M University that is very involved with the Texas nursery industry and, through its Extension Service, is helping homeowners and local nurseries in providing a wider variety of plants that will work there.

Odessa is a little colder and not quite as hot as Las Vegas, and the soils are better for plants than most of ours — better primarily because there is more decomposed plants and animal life in the soils and they receive more rainfall. West Texas is considered semi-arid, a part of the High Plains, while Las Vegas is in the eastern Mojave Desert.

Ornamental plums, some we call purple leaf plums, are actually fruit-bearing trees that are sold for ornamental landscapes because of their showy flowers. They are from a group of fruit trees collectively called cherry plums. Actually, some cherry plums have purple foliage and some have green.

Two popular purple varieties are Thundercloud and Atropurpurea. Cherry plums require a pollenizer (another tree similar but distinctly different) to set fruit. If no pollenizer is nearby, then there is little or possibly no fruit.

Some cherry plums will set a few fruit by themselves but will set many more fruit if a pollenizer tree is close by. Fruit set without a pollenizer can depend on the climate as well. Late frosts after flowering can cause any fruit that might set to fail.

The types of borers present vary with the climate and geographical location. Also, borers are transported inside nursery plants between states. This is one method they have for getting around — by truck.

If a state like Nevada is dominated with nursery plants grown in California, these plants are more likely to have pests common to California. If plants are bought from nurseries in Texas (Texas has a large nursery industry as well), then the pests are more likely to be pests common to Texas.

Borers are decomposers. They are attracted to plants that are weakened or damaged. Our intense sunlight is tough on plants and can weaken them. Our soils are poor and can lead to unhealthy plants as well. These all make a nice hunting ground for borers.

Q: Why can’t I find St. Augustine grass here in Las Vegas. It does well in Odessa, Texas, a similar climate.

A: St. Augustine grass, grown in Arizona, does very well here and was offered for sale during the late 1980s and early 1990s. It never became popular. People in Southern Nevada preferred the all-green, winter lawn that tall fescue provided.

Overseeding Bermuda grass in the fall for a green winter lawn is not possible with St Augustine grass. Even if it could be overseeded, the winter brown lawn that St. Augustine grass provided was a hard sell for Las Vegans.

Generally, there is a lack of enthusiasm here for the warm season grasses such as Bermuda grass, Zoysiagrass, Buffalograss, St. Augustine and Seashore Paspalum. These are a few of the reasons Southern Nevada is different, horticulturally, from Odessa, Texas.

Q: I have an 18-year-old Desert Museum palo verde in my front yard. One of the limbs has two places where the sap is leaking and dripping to the ground. The sap also has hardened on the limb. Do you have any thoughts on what is causing this?

A: Sap being pushed from the limbs of many trees is very common. This includes palo verde. Sap oozing from limbs is frequently a sign of damage or stress. Cut or broken limbs can ooze sap.

Stress from watering too often can cause sap to ooze from the trunk or large limbs. Realize that this is a desert tree and that watering too frequently can damage or kill this tree.

Sometimes you can diagnose problems by looking at the sap. If the sap is clear and not cloudy or murky than this can be a good sign. However, if the sap is cloudy or murky or filled with debris, then this can be a sign something destructive is happening inside the tree.

At this point, just keep an eye on it and be careful of your irrigations. When you irrigate, put a lot of water on it once and then don’t irrigate again for a week or two. Palo verde responds to water by growing more and having a fuller canopy.

When water is limiting, growth begins to slow down and the leaves drop from the tree. Let the tree dictate how much water it needs by observing its growth and shade from its canopy.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to [email protected]

Understanding and Applying Chelated Fertilizers Effectively Based on Soil pH1

Guodong Liu, Edward Hanlon, and Yuncong Li2

Plant nutrients are one of the environmental factors essential for crop growth and development. Nutrient management is crucial for optimal productivity in commercial crop production. Those nutrients in concentrations of ≤ 100 parts per million (ppm) in plant tissues are described as micronutrients and include iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chlorine (Cl), molybdenum (Mo), and nickel (Ni). Micronutrients such as Fe, Mn, Zn, and Cu are easily oxidized or precipitated in soil, and their utilization is, therefore, not efficient. Chelated fertilizers have been developed to increase micronutrient utilization efficiency. This publication provides an overview of chelated fertilizers and considerations for their use to county Extension faculty, certified crop advisers (CCAs), crop consultants, growers, and students who are interested in commercial crop production.

What is chelated fertilizer?

The word chelate is derived from the Greek word chelé, which refers to a lobster’s claw. Hence, chelate refers to the pincer-like way in which a metal nutrient ion is encircled by the larger organic molecule (the claw), usually called a ligand or chelator. Table 1 lists common natural or chemical synthetic ligands (Havlin et al. 2005; Sekhon 2003). Each of the listed ligands, when combined with a micronutrient, can form a chelated fertilizer. Chelated micronutrients are protected from oxidation, precipitation, and immobilization in certain conditions because the organic molecule (the ligand) can combine and form a ring encircling the micronutrient. The pincer-like way the micronutrient is bonded to the ligand changes the micronutrient’s surface property and favors the uptake efficiency of foliarly applied micronutrients.

Why is chelated fertilizer needed?

Because soil is heterogeneous and complex, traditional micronutrients are readily oxidized or precipitated. Chelation keeps a micronutrient from undesirable reactions in solution and soil. The chelated fertilizer improves the bioavailability of micronutrients such as Fe, Cu, Mn, and Zn, and in turn contributes to the productivity and profitability of commercial crop production. Chelated fertilizers have a greater potential to increase commercial yield than regular micronutrients if the crop is grown in low-micronutrient stress or soils with a pH greater than 6.5. To grow a good crop, crop nutrient requirements (CNRs), including micronutrients, must be satisfied first from the soil. If the soil cannot meet the CNR, chelated sources need to be used. This approach benefits the plant without increasing the risk of eutrophication.

Several factors reduce the bioavailability of Fe, including high soil pH, high bicarbonate content, plant species (grass species are usually more efficient than other species because they can excrete effective ligands), and abiotic stresses. Plants typically utilize iron as ferrous iron (Fe2+). Ferrous iron can be readily oxidized to the plant-unavailable ferric form (Fe3+) when soil pH is greater than 5.3 (Morgan and Lahav 2007). Iron deficiency often occurs if soil pH is greater than 7.4. Chelated iron can prevent this conversion from Fe2+ to Fe3+.

Applying nutrients such as Fe, Mn, Zn, and Cu directly to the soil is inefficient because in soil solution they are present as positively charged metal ions and will readily react with oxygen and/or negatively charged hydroxide ions (OH-). If they react with oxygen or hydroxide ions, they form new compounds that are not bioavailable to plants. Both oxygen and hydroxide ions are abundant in soil and soilless growth media. The ligand can protect the micronutrient from oxidization or precipitation. Figure 1 shows examples of the typical iron deficiency symptoms of lychee grown in Homestead, Florida, in which the lychee trees have yellow leaves and small, abnormal fruits. Applying chelated fertilizers is an easy and practical correction method to avoid this nutrient disorder. For example, the oxidized form of iron is ferric (Fe3+), which is not bioavailable to plants and usually forms brown ferric hydroxide precipitation (Fe(OH)3). Ferrous sulfate, which is not a chelated fertilizer, is often used as the iron source. Its solution should be green. If the solution turns brown, the bioavailable form of iron has been oxidized and Fe is therefore unavailable to plants.

In the soil, plant roots can release exudates that contain natural chelates. The nonprotein amino acid, mugineic acid, is one such natural chelate called phytosiderophore (phyto: plant; siderophore: iron carrier) produced by graminaceous (grassy) plants grown in low-iron stress conditions. The exuded chelate works as a vehicle, helping plants absorb nutrients in the root-solution-soil system (Lindsay 1974). A plant-excreted chelate forms a metal complex (i.e., a coordination compound) with a micronutrient ion in soil solution and approaches a root hair. In turn, the chelated micronutrient near the root hair releases the nutrient to the root hair. The chelate is then free and becomes ready to complex with another micronutrient ion in the adjacent soil solution, restarting the cycle.

Figure 1.

Typical iron deficiency symptoms of lychee (Litchi chinensis, the soapberry family).

Credit:

Yuncong Li, UF/IFAS

Chemical reactions between micronutrient chelates and soil can be avoided by using a foliar application. Chelated nutrients also facilitate nutrient uptake efficiency for foliar application because crop leaves are naturally coated with wax that repels water and charged substances, such as ferrous ions. The organic ligand around the chelated micronutrient can penetrate the wax layer, thus increasing iron uptake (Figure 2). Compared to traditional iron fertilization, chelated iron fertilization is significantly more effective and efficient (Figure 3) than non-chelated fertilizer sources.

Figure 2.

Schematic diagram of chelated fertilizers facilitating nutrient uptake for foliar application. Without chelation (aqua), micronutrients stay on the leaf surface. With chelation (aqua surrounded by blue), micronutrients first move into the mesophyll and then release micronutrients. Color key: aqua = a micronutrient ion; blue = organic ligand; dark green = wax layer on leaves; light green = mesophyll.

Credit:

Fullerton (2004)

Figure 3.

Comparison of foliar applications of chelated Fe, regular iron fertilizers, and no iron fertilization for correcting iron deficiency of lychee (Litchi chinensis, the soapberry family).

Credit:

Yuncong Li, UF/IFAS

Therefore, chelated fertilization can improve micronutrient use efficiency and make micronutrient fertilization more cost effective. The images in Figure 3 show the difference in three treatments with lychee: chelated Fe(II) is greener than FeSO4 plus sulfuric acid, and FeSO4 plus sulfuric acid is greener than no iron fertilization (Schaffer et al. 2011).

Which crops often need chelated fertilizers?

Vegetable and fruit crop susceptibility to micronutrients differs significantly (Table 2). For those in the highly or moderately susceptible categories, chelated fertilizers are often needed. For those with low susceptibility, no chelated fertilizers are needed unless the soil is low in micronutrient bioavailability, as demonstrated by a soil test. Soil pH is a major factor influencing micronutrient bioavailability; therefore, if soil pH is greater than 6.5, then the soil may have limited micronutrient bioavailability (Poh et al. 2009), and chelated fertilizers may be needed.

Which chelated fertilizer should be used?

Each of the ligands (Table 1) can form a chelated fertilizer with one or more micronutrients. The effectiveness and efficiency of a particular chelated fertilizer depends on the pH of the plant growth medium.

The ligands EDTA, DTPA, and EDDHA are often used in chelated fertilizers (Table 4). Their effectiveness differs significantly. EDDHA chelated Fe is most stable at soil pH greater than 7 (Figure 4, A and B). Chelated fertilizer stability is desired because it means the chelated micronutrient will remain in a bioavailable form for a much longer time period, thus increasing micronutrient use efficiency in vegetable and fruit production. The stability of three typical chelated Fe fertilizers varies at different pH conditions (Figure 4, A). The Y-axis represents the ratio of chelated Fe to total chelate and ranges from 0 to 1.0. A value of 1.0 means the chelate is stable. The X-axis represents soil pH. At 6.0, the ratios for all three chelated Fe fertilizers are 1.0 (stable), but at pH 7.5, only the ratio of EDDTA chelated Fe is 1.0. That of DTPA chelated Fe is only 0.5, and that of EDTA chelated Fe is only 0.025. So, in practice, EDDTA chelated Fe fertilizer is most effective when pH is greater than 7 but most costly. Accordingly, crop yields of these three chelated fertilizers are in this order: FeEDDHA > FeDTPA > FeEDTA (Figure 4, B). See Micronutrient Deficiencies in Citrus: Iron, Zinc, and Manganese (http://edis.ifas.ufl.edu/ss423) for effective pH ranges of iron chelates. Table 3 shows the relationship between soil pH and chelated fertilizer requirement.

Correction of Fe deficiency depends on individual crop response and many other factors. For instance, for vegetables, the rate is usually 0.4–1 lb. chelated Fe in 100 gal. of water per acre. Deciduous fruits need 0.1–0.2 lb. chelated Fe in 25 gal. of water per acre (Table 5). Foliar application is more effective than soil application. For foliar application, either inorganic or chelated Fe is effective, but for fertigation, chelated Fe should be used. In high pH soil, crops are also vulnerable to Cu deficiency stresses. Chelated Cu is significantly more effective than inorganic Cu. A commonly used copper chelate is Na2CuEDTA, which contains 13% Cu. Natural organic materials have approximately 0.5% Cu (Table 5).

In addition to soil pH, Mn is also influenced by aeration, moisture, and organic matter content. Chelated Mn can improve Mn bioavailability. Mn deficiency occurs more often in high pH and dry soil. Similar to other micronutrients, foliar spray is much more effective than soil application. For commercial vegetable production, 0.2–0.5 lb. MnEDTA in 200 gal. of water per acre can effectively correct Mn deficiency (Table 5). Zinc is another micronutrient whose bioavailability is closely associated with soil pH. Crops may be susceptible to Zn deficiency in soil with pH > 7.3. Spraying 0.10–0.14 lb. chelated Zn in 100 gal. of water per acre is effective (Poh et al. 2009). Animal waste and municipal waste also contain Cu, Mn, and Zn micronutrients (Table 5). For more information about micronutrient deficiency in crops, see Plant Tissue Analysis and Interpretation for Vegetable Crops in Florida (http://edis.ifas.ufl.edu/ep081), Micronutrient Deficiencies in Citrus: Iron, Zinc, and Manganese (http://edis.ifas.ufl.edu/ss423), and Iron (Fe) Nutrition of Plants (http://edis.ifas.ufl.edu/ss555).

Practical Take-Home Message

  • High pH soil (pH > 6.5) often has low bioavailability in micronutrients such as Fe, Mn, Zn, and Cu, and micronutrient fertilizers are needed for commercial crop production.

  • Crop susceptibility to the above micronutrient deficiencies depends on the plant species and cultivar. Commercial crops can be categorized into three susceptibility groups: high, medium, and low. The first two groups often need chelated fertilizers.

  • Inorganic water-soluble micronutrient application to the soil is often ineffective for correcting micronutrient disorders.

  • Chelated fertilizers are less reactive to soil conditions and can significantly enhance nutrient uptake and utilization efficiencies.

  • Chelate fertilization rates range from 0.2 to 1 lb. micronutrient per acre for vegetable production and 0.1–0.5 lb. micronutrient per acre for fruit production.

  • Foliar application of chelated fertilizers is often more effective than soil application.

Lindsay, W. L. 1974. “Role of Chelation in Micronutrient Availability.” In The Plant Root and Its Environment, edited by E. E. Carson, 507−524. Charlottesville: University Press of Virginia.

Morgan, B., and O. Lahav. 2007. “The Effect of pH on the Kinetics of Spontaneous Fe (II) Oxidation by O2 in Aqueous Solution – Basic Principles and a Simple Heuristic Description.” Chemosphere 68(11): 2080–2084.

Tables

Table 1.

Common synthetic and natural chelate compounds (ligands).

Abbreviation

Name

Formula

CDTA

Cyclohexanediaminepentaacetic acid

C14H22O8N2

CIT

Citric acid

C6H8O7

DTPA

Diethylenetriaminepentaacetic acid

C14H23O10N3

EDDHA

Ethylenediaminediaminedi-o-hydroxyphenylacetic acid

C18H20O6N2

EDTA

Ethylenediamintetraacetic acid

C10H16O6N2

EGTA

Ethylene glycol bis(2-aminoethyl ether) tetraacetic acid

C14H24O10N2

HEDTA

Hydroxyethylenediaminetriacetic acid

C10H18O7N2

NTA

Nitrilo-triacetic acid

C6H9O6N

OX

Oxalic acid

C2H2O4

PPA

Pyrophosphoric acid

H4P2O7

TPA

Triphosphoric acid

H5P3O10

Source: Havlin et al. (2005); Sekhon (2003)

Table 2.

Selected vegetable and fruit crop species’ relative susceptibility* to some micronutrient deficiencies.

Cu

Fe

Mn

Zn

Vegetable

Asparagus

Medium

Low

Bean

Low

High

High

High

Broccoli

Medium

High

Medium

Cabbage

Medium

Medium

Medium

Medium

Cauliflower

Medium

High

Medium

Carrot

High

Medium

Low

Celery

Medium

Medium

Cucumber

Medium

High

Lettuce

High

High

Medium

Mustard/crucifers

Low

Onion

High

High

Pea

Low/medium

Medium

High

Low

Potato

Low

Low

High

Medium

Radish

Medium

High

Spinach

High

High

High

Medium

Sweet corn

Medium

Medium

Medium

High

Tomato

Medium

High

Medium

Medium

Turnip

Medium

Fruit

Apple

Medium

High

High

Deciduous

Medium

High

High

High

Citrus

High

High

High

High

Grape

Medium

High

High

High

Raspberry

High

High

Strawberry

Medium

High

High

* The high category needs micronutrient fertilization; the medium category probably needs fertilization; the low category usually does not need fertilization.

Note: Cultivars often respond differently to low soil micronutrient conditions. Check with your seed or transplant supplier about the attributes when selecting a cultivar source.

Source: Alloway (2008); Havlin et al. (2005)

Table 3.

Soil pH and chelated fertilizer requirements in commercial crop production.

Soil pH < 5.3

Soil pH ranges from 5.3 to 6.5

Soil pH > 6.5

No chelated fertilizers are needed.

Chelated fertilizers may be needed.

Chelated fertilizers are needed.

At soil pH 5.3 or lower, soil can generally provide sufficient Fe, Cu, Mn, and Zn. In the soil pH range from 5.3 to 6.5, highly susceptible crop species may need chelated fertilizers. At soil pH 6.5 or greater, most crops need chelated fertilizers.

Table 4.

Chelated fertilizers, formula, and nutrient content (%).

Source

Formula

Nutrient (w/w, %)

Iron chelates

NaFeEDTA

5–14

NaFeEDDHA

NaFeDTPA

Copper chelates

Na2CuEDTA

13 Cu

Na2CuHEDTA

Manganese chelates

Na2MnEDTA

5–12 Mn

Zinc chelates

Na2ZnEDTA

14 Zn

Na2ZnHEDTA

9–13 Zn

Natural organic materials

5–10 Fe, 0.5 Cu, 0.2 Mn, 1–5 Zn

Table 5.

Examples of chelated fertilization rates for selected commercial vegetable and fruit crops.

Footnotes

This document is HS1208, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date November 2012. Revised September 2015 and December 2018. Visit the EDIS website at https://edis.ifas.ufl.edu for the currently supported version of this publication.

Guodong Liu, associate professor, Horticultural Sciences Department; Edward Hanlon, professor emeritus; and Yuncong Li, professor, Department of Soil and Water Sciences; UF/IFAS Extension, Gainesville, FL 32611.

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.

Milorganite’s Iron Guarantee

By Jaime Staufenbeil – Milorganite Agronomist
June 13, 2017

Nutrient amounts in Milorganite, including iron, are guaranteed

Milorganite’s iron guarantee recently changed from 4% to 2.5%. Our faithful customers have expressed concern that less iron in Milorganite may not produce the same green lawns they’ve grown to expect. We’d like to address your concerns and explain the change in analysis.

The analysis on every bag of fertilizer, including Milorganite, guarantees the minimum amount of specific nutrients. The analysis is highly regulated, so rest assured, it’s accurate. The analysis for Milorganite, 6­–4–0, guarantees there’s a minimum of 6% nitrogen, 4% phosphorus, and less than one percent potassium in each bag. There’s one additional nutrient in Milorganite that has made it so popular among homeowners for decades: iron. Iron helps promote the green lawn homeowners desire.

Why is there less iron in Milorganite?

Nutrient levels in Milorganite have fluctuated throughout its 90-year history as a result of the wastewater reclamation and Milorganite production processes. Iron, which doesn’t naturally occur in high quantities in wastewater, has traditionally been used as an effective additive to bind and recover phosphorus and continues to be the primary source of iron in Milorganite. Improvements to our water reclamation operations have reduced the amount of iron needed to maximize phosphorus recovery, improving overall water quality and increasing the phosphorus (P) guarantee of Milorganite from 2% to 4%. As a result, Milorganite’s guaranteed iron has changed from 4% to 2.5%. The overall benefits of Milorganite to lawns, landscapes, and gardens remain the same.

Research demonstrates Milorganite’s ability to green-up lawns doesn’t change with a revised iron guarantee

We conducted independent research a few years ago to ensure that, despite any changes in the iron guarantee, Milorganite continues to provide homeowners the outcomes they expect— lawns that are healthy, with a long-lasting, deep-green color.

We studied both northern and southern grasses to determine how various amounts of iron and nitrogen in Milorganite affected the greenness of lawns. The study of northern grasses was conducted through the University of Wisconsin – Madison, Department of Soil Science.

Two measures were used to evaluate how green the lawn was for each fertilizer mix: one electronic (color index) and the other visual. Under the conditions of the study, both measures were found to be statistically similar to the Milorganite mix with 5.1% iron, as well as the mix with 2.3% iron (see table below). The different levels of iron “…did not significantly affect the color response of the grass.”

Average Color Index

Treatment Color Index Visual Quality
Milorganite 2.3% Iron 394 6.7
Milorganite 5.1% Iron 406 6.8

A 2015 study conducted in Florida by George H. Snyder, Ph.D. compared Bahiagrass grown with various fertilizer treatments, including three of Milorganite with varying amounts of iron—2%, 2.7%, and 4%. The year-long study concluded that “Throughout the study, no differences in leaf appearance or growth were observed among the three Milorganite sources.”

Iron in Milorganite

There are benefits for your lawn when using chelated iron—iron treated to make it water-soluble, which can be expensive. Iron salts are less expensive but have drawbacks, including the potential for burning plants and staining concrete surfaces.

The iron in Milorganite works like chelated iron, but without the expense. It also won’t burn your lawn and releases into the soil where plants need it, compared to foliar applications (applying liquid directly to leaf) of iron that is gradually removed when the lawn is mowed. Milorganite, including its iron, breaks down slowly and is available to plants as microorganisms in the soil use it as a food source. It’s non-staining, so there’ll be no rust stains on your driveway or walkways. It’s also long-lasting, which means fewer applications compared to other types of iron. Best of all, with Milorganite’s iron, you’ll have a deep green lawn!

We don’t recommend using a variety of iron supplements on your lawn. Lawns can use only a limited amount of any nutrient, including iron. Over application can result in run-off into waterways and it’s a waste of money.

Lawn visual quality impacted by more than iron

There are a number of factors that can affect the visual quality of your lawn aside from iron, including temperature, moisture, weeds, diseases, insects, and even cloud cover.

Continue to use Milorganite with confidence

None of us like change, even changes in a product like Milorganite, which you’ve trusted for years. There have always been fluctuations in Milorganite’s nutrient guarantee and we may see changes in the future as processes continue to improve. We will always be honest with you—our faithful customers—and provide accurate information.

Along with Milorganite’s nutrient guarantee, we guarantee we will continue to provide a high-quality product that produces the healthy, green lawns you’ve all grown to expect.

Chelated Iron EDTA Fertilizer – 13% Fe

Iron (Fe) is one of the most important micro-nutrients required for plants, trees, and lawn. Although most soils have plenty of Iron (Fe), usually it’s not available for plants and that’s why Iron (Fe) deficiency is very common in plants and it is also known as chlorosis (yellowing of leaves). Some of common Iron Chelate EDTA features:

  • Great To Improve or Prevent Chlorosis (Yellowing of Leaves)
  • Great For Foliage Usage (100% Water Soluble)
  • Contains 13% Iron EDTA
  • Suitable for Hydroponics and Soil Usage

NOTE: Your choice of Nitrogen (N) fertilizer is also very important for Iron (Fe) uptake in plants. Ammonium Nitrogen (N) is the most efficient form of Nitrogen (N) because it lowers the pH level in roots; therefore, increase Iron (Fe) uptake. In contrast, Nitrate Nitrogen (N) would increase the pH level and lower the Iron (Fe) uptake in plants.

NOTE: Applying Chelated Iron EDTA could definitely solve Iron (Fe) deficiency problems in the short term but it is very important to identify the problem and prevent it from happening instead of applying Iron (Fe) fertilizer which could become very expensive.

APPLICATION RATE:

Soil Application: 13% Chelated Iron is recommended for use on acid and mildly alkaline soils. To ensure uniform coverage, IRON CHELATE should be dissolved in water or fluid fertilizer, or dry blended with water soluble fertilizers. For trees or individual plants, the chelate may be blended with an inert (such as soil or sand) or sprinkled directly on the soil uniformly under the plant’s drip line, then watered in. Soil applications may also be made by dissolving in water and then mixing or metering into drip, sprinkler or furrow irrigation systems.

Foliar Application: Iron Chelate may be applied in water or in combination with most pesticides. After the correct dilution has been made, the spray solution should be buffered to pH 6-6.5. Thorough coverage and the use of wetting agents often enhance nutrient uptake from foliar sprays. Application rates and dilution factors depend on crop sensitivity, the amount of foliage to be sprayed and the application method. Avoid applying this product when plants are suffering from moisture stress. If there is any doubt, apply the spray solution to a small test area of the crop or foliage to assess any undesirable effects or phytotoxicity before general application.

SOIL APPLICATION RECOMMENDATIONS:

Ornamental Shrubs and Trees: including azaleas, gardenias, junipers, pines, roses: 2 Tbsp. for small shrubs and up to 2 Tbsp. per inch of tree diameter for large trees and shrubs

Turf: 3/4 lb. per 1,000 sq. ft. or 33 lbs. per acre

NOTE: The rates given above are based on broadcast application. If broadcast rates are used for spot or banded applications, phytotoxicity may result.

FOLIAR APPLICATION RECOMMENDATIONS:

Trees (Citrus): Apply 1 – 2 lbs. per 100 gallons of cover spray any time except during bloom.

Trees & Vine Crops (Excluding Citrus Trees): Apply 1 – 2 lb. per acre in sufficient spray volume for thorough coverage (25-gallon minimum) at dormant/delayed dormant before bloom, then after full bloom at 2 3-week intervals as needed. NOTE: For smooth skinned fruit (peach, pear, apple, etc.) apply 1 lb. per acre in 50-100 gal. of water.

Vegetable & Field Crops: Apply a third – one and a third lb. per acre in sufficient spray volume for thorough coverage (25-gallon minimum)

Related Blog Posts:

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Documentations:

  • Material Safety Data Sheet

Iron is an essential nutrient needed by plants to function. Chelated iron like this is water soluble iron supplements plants can easily use. But we’re getting ahead of ourselves.

Iron is used up in some of the most vital functions of plants, such as:

  • Chlorophyll and enzyme production
  • Nitrogen fixation
  • Metabolism and development

For this reason, plants simply cannot function as they should without the presence of iron or iron supplementation.

The symptoms of iron deficiency in plants can be spotted with yellow leaves, usually between the dark green veins, which gives the leaf a spidery look. Plants and leaves lack that “healthy green” appearance.

This commonly referred to as lime chlorosis or iron chlorosis. With time, the leaves appear whitish, and start to die; resulting in stunted growth of the entire plant.

This can be quite frustrating to a gardener, especially with the unsightly yellow or whitish leaves. Chelated iron supplement is your best bet when treating iron chlorosis.

What Is Chelated Iron?

This is a soluble iron complex, primarily designed to make iron soluble in water for use in agricultural purposes.

In most cases, it comes as a darkish brown powder, and it can potentially be a mild irritant to the skin, eyes, and the respiratory membranes depending on the person.

A chelated iron fertilizer is one of the most popular and efficient methods of treating chlorosis.

In horticulture, chelated iron fertilizer is referred to as sequestered iron and serves as a plant tonic, where its mixed with other plant food products and nutrients.

For those who practice ornamental horticulture, iron chelate is widely recommended to feed plants such as Rhododendrons when the soil is calcareous.

Causes of Iron Chlorosis

Iron deficiency in plants is rarely caused by lack of iron in soil, because it is typically abundant in soil.

However, a variety of soil conditions may restrict the nutrient uptake of a plant to get iron from the soil. Here are some of the causes of iron chlorosis:

  • Too much clay in the soil
  • A very high pH for the soil
  • High phosphorous content in the soil
  • Overly wet or compacted soil

The first step in diagnosing chlorosis is by performing a soil test. Your local agricultural extension center should help with this.

Keep in mind that they can also test leaf samples to determine exactly what nutrient, micronutrient or mineral is missing.

Although you may find out that your soil lacks iron, the problem could be from one of the causes listed above.

Leaves bein to turn yellow with an Iron deficiency of Hydrangea macrophylla leaf – Iron chlorosis

Managing Iron Chlorosis

So, how to add iron to soil?

After iron deficiency is diagnosed, you can treat iron deficiency by applying an iron foliar spray. But always remember that the best solution is prevention.

In this case, you should determine the underlying cause of the deficiency, and focus on treating it so you prevent the same problem from occurring later.

Evaluating the different causes of iron deficiency and correcting them can save you a lot of time and money spent on unnecessary and ineffective iron applications.

In general, iron can be applied in chelated form or as a ferrous sulfate. Ferrous sulfate or ferric iron is comprised of about 20% iron. It’s quite an inexpensive fertilizer with iron, mainly used in foliar spraying.

In pH of above 7.0, it can be ineffective when applied as a soil application, since iron will quickly transform to Fe3, which precipitates as iron oxides do.

Iron chelates are much better because the compound has stabilized iron ions, ideally preventing it from oxidizing and in turn precipitating away. The chelates contain three components in their formula:

  • Fe3 ions
  • Ammonium (NH4 ) or Sodium (Na ) ions
  • A complex like DTPA, EDTA, EDDHA, citric acid, amino acid, or humic-fulvic acid

In essence, different iron chelators will hold different strength depending on the given pH levels.

Related Reading –> Lemon Trees Leaves Turning Yellow

Moreover, they differ in their vulnerability to iron ions replacement by other competitive ions. At high concentrations, magnesium or calcium ions can replace the iron ions in the chelate.

Chelated Iron EDTA: This compound is stable at a pH of below 6.0, and at levels above 6.5, almost 50% of the iron will be unavailable. This means that this chelating agent will be ineffective in alkaline soils.

Additionally, this chelate has a high affinity for calcium, and it should not be used in soils (or water) rich in calcium.

Iron DTPA chelate: Stable in pH levels of below 7.0. It’s also not as vulnerable to iron replacement by calcium as the ETDA.

Iron EDDHA chelate: usually stable at pH levels up to 11.0. however, it’s one of the most expensive chelates available.

Be sure to use chelates during spring, before growth starts with the correct application rates.

Sprinkle some dry chelated iron for plants on the soil and irrigate, or dissolve in water and apply the chelated liquid iron around the base of the plants.

Iron chelates can also be applied in the holes surrounding the drip line of the affected plants.

Correcting Iron Deficiency

Sophie Thomson

SOPHIE THOMSON: If you’ve got yellow leaves on your plant, there can be a number of causes. This one is showing signs of lime induced chlorosis. What we look for is plants with yellow leaves, but darker green veins. It occurs on the new growth and when it’s severe, it can actually cause the whole leaf to go pale yellow or almost white. It happens when the iron in the soil is locked up and not available to the plant and it affects many different plants.

It’s caused by alkaline soil, the application of alkaline water, putting on compost or mulch that’s quite alkaline such as spent mushroom compost and even the lime leeching out of the render on walls and buildings.

To correct this, apply iron chelates. This can be done as a folia spray where we simply put it in a sprayer bottle and spray it all over the leaves or mix it in a watering can and water it around the root zone. Within a week, the leaves will start to green up in the warmer weather and you’ll know you’re on the right track, however it will probably take a couple more applications every two to four weeks until you see the leaves go back to the dark green that they should be.

Treating your plants with iron chelates is, however, only a short-term solution to the symptoms of chlorosis and it doesn’t actually treat the soil. For a long-term solution, apply agricultural sulphur.

Treating iron induced chlorosis is easy and very quickly, you’ll see your plants greener and look great again.

STEPHEN RYAN: And now it’s off to the beach at Byron Bay where Colin discovered a native grass that’s helping to preserve our precious coastal environment.

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