Understanding Fertilizer Material

Understanding Fertilizer Material

There is great variety among fertilizer materials. In general, fertilizers fall within two major categories: commercial fertilizer sources and organic sources. While it is difficult to make direct comparisons between these two sources, a few loose comparisons can be made.

First, commercial sources are typically high analysis fertilizers, while organic sources are low analysis. This means that commercial fertilizers contain a larger percentage of a given nutrient than organic sources. As a result, commercial fertilizers are applied in lesser amounts than organic sources, since it take less commercial fertilizers to achieve a given rate.

Secondly, composition of organic fertilizer is generally much more varied than commercial fertilizers. This lack of consistency can make it difficult to predict how much organic fertilizers should be applied in order to obtain a desired rate.

Thirdly, commercial fertilizer production is fossil fuel intensive. As a result, the price of commercial fertilizer can be relatively expensive.

Commercial fertilizer sources


Anhydrous ammonium is the starting block for most inorganic nitrogen fertilizers. Anhydrous ammonium is manufactured by reacting N2 with H2 under extreme heat and pressure in the presence of a catalyst, known as the Haber-Bosch technology. The Haber-Bosch technology requires large energy input, but allows for the manufacture of high N analysis fertilizers.

Anhydrous Ammonium

  • Anhydrous ammonium has the highest nitrogen analysis out of all inorganic fertilizers
  • It is comprised of 82% nitrogen.
  • It must be kept under pressure since it evaporates under normal atmospheric pressure.
  • It is very harmful to human tissue, such as eyes, skin, and lungs. Thus, there are many safety precautions associated with the handling of NH3.

Ammonium sulfate

  • Contains 21% nitrogen and 11% sulfur
  • Sugarcane and pineapple production
  • Ammonium sulfate is acid forming and lowers soil pH.

Ammonium phosphate

Monoammonium phosphate (MAP)

  • 11-18% nitrogen and 48-55% P2O5
  • MAP is a water soluble fertilizer
  • The soil pH temporarily lowers to about 3.5 in areas where MAP initially reacts with soil.

Diammonium phosphate (DAP)

  • 18-21% nitrogen and 46-53% P2O5
  • DAP is a water soluble fertilizer.
  • The soil pH temporarily reduces to 8.5 in areas where DAP initially reacts with soil.
  • DAP may produce free ammonia in high pH soils, which may cause seed injury if placed too close to seed rows.

Potassium nitrate

  • 13% nitrogen and 44% K2O
  • Provides soil with readily available nitrate, which generally increases soil pH.

Calcium nitrate

  • 15% nitrogen and 34% CaO
  • Provides soil with readily available nitrate.
  • However, calcium nitrate is hygroscopic (absorbs moisture from air) and must be kept under air-tight storage conditions.


  • 45-46% nitrogen
  • Advantages of urea over other nitrogen sources include:
    • reduced caking of fertilizer material
    • less corrosion on equipment
    • decreased costs associated with storage, transportation, and handling
  • Once applied to the soil, an enzyme known as urease transforms urea to NH4+ and HCO3-.
    • This transformation readily occurs under warm, moist conditions.
  • Urea temporarily increases the pH of the soil it contacts, due to the initial release of NH3. However, the soil pH may ultimately decrease as the NH4+ nitrifies to NO3-, which is an acid producing reaction.
  • In soils with high pH, NH4+ may volatilize and escape from the soil in the form of NH3. Volatilization losses are reduced by incorporating or washing urea into the soil.
  • Urea can contain biurate, which is phytotoxic to most plants.
    • Although most plants tolerate up to 2% biurate levels, pineapple and citrus are sensitive to biuret. The urea should contain less than 0.25% biuret.

Sulfur-coated urea

  • 22-38% nitrogen and 12-22% sulfur
  • Sulfur-coated urea is a controlled release fertilizer.
    • It contains a coat of sulfur that surrounds a urea granule, which controls its release.
    • Urea is only released after the sulfur coat is oxidized by microorganisms.
    • The rate at which urea becomes available depends on the thickness of the sulfur coat.
  • Sulfur coated urea is advantageous in coarse textured soils and/or soils that have a great nitrate leaching potential.


The major source of inorganic phosphorus fertilizers is rock phosphate. Rock phosphate is a naturally occurring mineral, which is mined from the earth. Deposits of rock phosphate occur around the world, such as in the United States, Russia, Morocco, and China.

Rock phosphate (RP)

  • 27-41% P2O5 and 25% Calcium
  • The minerals that make up RP are various forms of apatite. The reactivity of RP depends on the type of apatite and its inherent purity. RP is not water soluble and only becomes available to plants under acidic conditions. RP is most reactive when it is finely ground and incorporated into warm, moist, acidic soils with long growing seasons. Although the availability of RP is slow, it has a great long term residual effect.


Single superphosphate (SSP)

  • 16-22% P2O5, 11-12% sulfur, and 20% calcium
  • SSP is manufactured by reacting RP with sulfuric acid.
  • SSP does not have a great influence on soil pH.

Triple superphosphate (TSP)

  • 44-52% P2O5, 1-1.5% sulfur, and 13% Ca
  • TSP is produced by treating RP with phosphoric acid
  • Like SSP, TSP does not have a great effect on soil pH.

Ammonium phosphate

Monoammonium phosphate (MAP)

  • 11-13% N, 48-62% P2O5, and 0-2% S
  • MAP is water soluble.
  • MAP temporarily lowers the soil pH to 3.5 in areas where MAP initially reacts with the soil.

Diammonium phosphate (DAP)

  • 18-21% N, 46-53% P2O5, and 0-2% S
  • DAP are water soluble.
  • The soil pH temporarily lowers to 8.5 in areas where DAP initially reacts.
  • DAP may produce free NH3 in soils with a high pH, which may cause seed injury if placed close to seed rows.


Potassium is mined from the earth as soluble potassium salts, or potash, with varying degree of purity. Canada is home to the world’s largest potash deposit.

Potassium chloride (muiate of potash)

  • 60-63% K2O
  • KCl is the most commonly used K fertilizer.
  • KCl readily dissolves in water

Potassium sulfate (sulfate of potash)

  • 50-53% K2O, 17% S K2SO4-
  • Potassium sulfate is completely water soluble.
  • In comparison to KCl, potassium sulfate:
    • has a lower salt index
    • may be used on crops that are sensitive to Cl- (i.e. avocado).

Potassium nitrate

  • 44% K2O and 13% N
  • Potassium nitrate is also water soluble.
  • Increases soil pH
  • Potassium nitrate is also a source of nitrogen.

Potassium-magnesium sulfate

  • 22% K2O, 11% Mg, and 22% S
  • This inorganic fertilizer does not have a significant effect on soil pH



  • Soil amendment which is commonly used to raise the pH of the soil.
  • Ground coral in Hawaii contains 38% Mg and 0.6% Mg

Calcium Carbonate

  • Approximately 38% Ca, depending upon its source
  • A common liming material, calcium carbonate also supplies calcium to the soil.


  • 22% Ca and 12% Mg, depending upon the dolomite source
  • In addition to raising the pH, dolomite is a source of calcium and magnesium.


  • 23% Ca and 19% S
  • Unlike liming materials, gypsum does not increase the soil pH.
  • In addition to providing calcium and sulfur, gypsum may be used to correct soil physical problems and/or aluminum toxicities.

Calcium nitrate

  • 15% N and 20% Ca
  • Calcium nitrate is very soluble in water.


Single (SSP)

  • 18-21% Ca
  • SSP supplies both calcium and phosphate.

Triple (TSP)

  • 12-14% Ca
  • Like SSP, TSP supplies both calcium and phosphate



  • 22% Ca and 12% Mg, depending upon the source
  • Dolomite is a source of both Ca and Mg, in addition to its liming affect.

Magnesium sulfate (Epsom salt)

  • 9.8% Mg and12% S
  • Epsom salt is very soluble and does not alter soil pH.

Magnesium oxide

  • 55% Mg
  • Magnesium oxide increases soil pH.
  • It is not highly water soluble. For maximum reactivity, it is often mixed into the soil.


Elemental sulfur

  • In its elemental form, sulfur is a solid
  • Elemental sulfur is insoluble in water.
  • When finely-ground elemental sulfur is incorporated into the soil, microorganisms oxidize and convert it to sulfate.
    • The finer the sulfur, the greater its oxidization potential when incorporated into the soil.

Ammonium sulfate

  • Contains 24% S and 21% N
  • Ammonium sulfate can have a strong acidifying effect on soil



  • Iron (ferrous) sulfate
    • Contains19% Fe
    • May be used as a foliar spray to correct Fe deficiencies
  • Iron chelate (iron EDTA)
    • Contains 5-14% Fe
    • May be used as foliar spray or directly applied to the soil
    • Though expensive, chelates prevent the formation of insoluble Fe compounds


  • Zinc sulfate
    • Contains 35% Zn
    • Due to its low soil mobility, zinc sulfate should be mixed into the soil when broadcasted
    • Band placement is favorable in finely textures soils that are low in Zn
    • Available as a foliar spray
  • Zinc chelate (EDTA)
    • Contains 14% Zn
    • May be applied as a foliage spray or directly to the soil
    • Zn chelates are very soluble and may be incorporated into liquid fertilizers


  • Copper sulfate
    • Contains 25% Cu
    • May be applied to the soil and/or foliage
    • Incorporating Cu into the plant root zone increases the efficiency of Cu
  • Copper chelate (EDTA)
    • Contains 13% Cu
    • Very soluble
    • May be applied as a foliar spray


  • Mangenese sulfate
    • Contains 26-28% Mn
    • May be applied as a foliar spray and/or directly to the soil in a band application
  • Manganese chelate (EDTA)
    • Contains 5-12%
    • Not recommended as a broadcast


  • Sodium borate, or borax
    • Contains 11% B
    • May be applied to soil as a band or broadcast
    • Available as a foliar spray
    • Since boron has a small sufficiency range, it should be mixed uniformly into the soil
    • Care should be taken to prevent B toxicity.
  • Sodium tetraborate
    • Contains14-15%
    • Most widely used B fertilizer


  • A manufactured product that contains 5.4% Fe, 5.2% Zn, 5.6% Mn, 5.4% Mg, 2.6% Cu, and 0.5% B. Since it is largely insoluble, it should be incorporated into the soil.

Blends (Mixed Fertilizers)

There are many available inorganic fertilizers that contain various combinations of N, P, and K fertilizers. If a particular formulation of N, P, and K is desired, a blend can conveniently meet the needs of the farmer or gardener, while reducing the costs associated with buying and applying multiple fertilizers.

Fertilizer Calculations

When applying fertilizers to your field or garden, you will add fertilizers at a specific rate of application. To accomplish this goal, it is necessary that you can perform two calculations:

  • First, you must know how to determine the percentage of nutrients, particularly N, P, and K, that a particular fertilizer contains.
  • Secondly, you must know how to calculate the quantity of fertilizer that must be added to a given area in order to achieve the recommended rate of fertilization for a particular nutrient.

The following provides a detailed explanation of how to perform these calculations, which was prepared and written by Jay Deputy of Tropical Plants and Soil Science.

Fertilizer Application Calculations

The major nutrients

A complete fertilizer contains all three of the major nutrient elements nitrogen (N), phosphorus (P), and potassium (K).
The total percentage of the nutrients contained in a fertilizer is given as three numbers, which together is known as the analysis. These numbers are usually in large print on the front of the container or bag. An example would be 10-30-10.

Nitrogen (N)

Nitrogen is reported as total N and may take one of three chemical forms:

  • NO3 or nitrate-N
  • NH4 or ammonium-N
  • Urea-N

Most fertilizers contain a mixture of two or all three of these N forms.

The percent of total-N is represented by the first of the three analysis numbers. For example, a bag with an analysis of 10-30-10 contains 10% N by weight of all nitrogen forms. Therefore, a 50 pound bag of 10-30-10 contains 5 pounds of total-N, which accounts for 10% of the bag’s 50 pounds weight.

Calculation of %N: 10% of 50 pounds = (.10 x 50 pounds) = 5 pounds of total N

Phosphorus (P)

Phosphorus is never present as pure elemental P. Instead, P is reported in fertilizers as the chemical compound P2O5 or ortho-phosphate. The percent of P2O5 in a complete fertilizer is represented by the second of the three analysis numbers. For example, a bag with the analysis of 10-30-10 contains 30% P2O5 by weight. Therefore, a 50 pound bag of 10-30-10 contains 15 pounds of P2O5.

Calculation of % P2O5: 30% x 50 pounds = (.30 x 50 pounds) = 15 pounds of P2O5

However, notice that the above calculation determines the amount of P2O5 in the bag of fertilizer, rather than the amount of total P. To report the quantity of total P, the percent of elemental, or pure, P must be determined.

To calculate elemental P, we must determine the percent by weight of P in P2O5, which is 44%. Thus, 44% of P2O5 is elemental P. To convert the percent of P2O5 to percent elemental P, multiply the percent P2O5 by 44%.

Therefore, a bag of 10-30-10 contains 15 pounds of P2O5 (see above calculation) and 6.6 pounds elemental P (15 pounds P2O5 x .44 = 6.6 pounds P)

Calculation of % P = % P2O5 x 44% = 15 pounds P2O5 (see above calculation) x .44 = 6.6 pounds of P

Potassium (K)

Potassium is also never present as pure elemental K, but is reported as its oxide form of K2O, commonly called potash. The percent of K2O in a bag of blended fertilizer is represented by the third of the three numbers of the analysis. For example, a bag of fertilizer with an analysis of 10-30-10 contains 10% K2O by weight. Therefore, a 50 pound bag of 10-30-10 contains 5 pounds of K2O 10% of 50 pounds.

Calculation of % K2O = 10% of 50 pounds = (.10,x 50) = 5 pounds of K2O

As with P, in some cases potassium is reported as percent elemental (or pure) K. To calculate elemental K, we must determine what percentage (by weight) of K2O is elemental K, which we know to be 83%. This means that 83% of K2O is elemental K. To convert percent K2O to percent elemental K, multiply the percent K2O by 83%.

Therefore, a bag of 10-30-10 contains 5 pounds of K2O (see above calculation) and 4.15 pounds elemental K

Calculation of % K = % K2O x 83% = 5 pounds K2O x .83 = 4.15 pounds elemental K

Calculating fertilizer application rates

The recommended amount of fertilizer to be applied to a crop at any one time has been experimentally determined for the major nutrients. In most cases, the most essential nutrient under consideration is nitrogen. In the case of turfgrass nutrition, the recommended amount of fertilizer per application is given in terms of pounds of nitrogen per acre or per 1000 square feet. The normal recommended rate for turf is one pound N per 1000 sq. ft. The frequency of applications will vary with the species of turfgrass.

In order to calculate the total amount of fertilizer being applied at any one time, several things need to be considered. These are:

  • Recommended rate in terms of pounds of N per 1000 square foot.
  • The analysis of the fertilizer being used. (The quantity of N that the fertilizer contains, which is indicated by the first number of the analysis.) Keep in mind — the lower the N %, the more fertilizer that will be required.
  • The total area being fertilized.
  • Must be mathematically calculated depending upon the overall shape of the plot

Once these have been determined, the following calculation will give the total amount of fertilizer needed to cover the designated area.
(Rate of N / 1000 sq. ft) X (Area in sq. ft) / (% N in fertilizer) = Pounds of fertilizer

Remember that when working with percentage figures, convert to a decimal before calculating. Therefore, convert 33% N to .33 for the calculation

Example 1 
Using a fertilizer with analysis 33-5-5 at a rate of one pound N/1000 ft2, how much fertilizer is required to cover a turf plot that measurers 100 ft x 50 ft.
First calculate the area of the plot,
area = L x W 100 x 50 = 5000 ft2
(Rate of N / 1000 sq. ft) X (Area in sq. ft) / (% N in fertilizer) = Pounds of fertilizer

Example 2 
(1 lb /1000 sq ft) X 5000 sq. ft / .33 = 15.15 lb of 33-5-5 fertilizer
This time use a different fertilizer, 20-5-10 at the same rate on the same plot of turf
(1 lb /1000 sq ft) X 5000 sq. ft / .20 = 25 lb of 20-5-10 to cover the same area

Why the difference?

33-5-5 contains more N per pound of fertilizer, and therefore, requires less material to provide one pound of N / 1000 ft2. However, this is not the only criteria that should be used in deciding what analysis to use. The nitrogen formulation is often a more important consideration.

Organic sources

Proper maintenance of soil organic matter is an important part of nutrient management, as increasingly supported by the scientific community. Organic matter enhances both chemical and biological soil properties, as well as supplying sources as macro- and micronutrients. The most stable form of organic matter—humus—plays an all-important role in improving soil structure, nutrient retention, and water storage. Additionally, it has been shown that additions of animal and green manures, as well as compost, enriched microbial diversity and populations.


Animal manure

The amount of nitrogen that manure provides and its subsequent availability to plants is influenced by a several factors:

  • Nutrient analysis of the animal feed
  • Storage and handling procedures of the manure
  • Amount and type of materials added to the manure
  • Timing and method of application
  • Properties of the soil
  • Choice of crop

Nitrogen Analysis

  • Manures can contain between 0.5 and 6% total nitrogen, though typical values range from 0.5 to 1.5%.
  • Of the total nitrogen, approximately only 25% to 50% is in the form of ammonium and directly available to plants./li>
  • The remaining 50-75% is organic nitrogen and must be mineralized before it is utilized by plants. Thus, the same conditions for optimal mineralization of organic matter are the same for the optimal mineralization of organic nitrogen in manure.

Organic Nitrogen

Organic nitrogen is further divided into two categories:

  • unstable organic nitrogen
  • stable organic nitrogen

Unstable organic nitrogen

  • urea or uric acid are the primary forms of unstable organic nitrogen
  • mineralization into ammonium occurs rapidly
  • highly vulnerable to volatilization and denitrification losses
  • it is recommended that manure be incorporated into the soil to prevent nitrogen losses to the atmosphere

Stable organic nitrogen

  • mineralizes at much slower rates than the unstable fraction
  • the stable nitrogen that is less resistant to decomposition (approximately 30% to 60% of the total nitrogen) mineralizes during the first year of application
  • the stable nitrogen that is more resistant to decomposition mineralizes during the following years with declining rates of mineralization each year that passes

The following table contains nutrient analysis information for various types of animal manures and composts.

Table 9. Nutrient Composition of Various Types of Animal Manure and Compost (all values are on a fresh weight basis).

Manure Type

Dry Matter


Total Na





————————- lb/ton —————————

Swine, no bedding






Swine, with bedding






Beef, no bedding






Beef, with bedding






Dairy, no bedding






Dairy, with bedding






Sheep, no bedding






Sheep, with bedding






Poultry, no litter






Poultry, with litter






Turkey, no litter






Turkey, with litter






Horse, with bedding






Poultry compost






Dairy compost






Mixed compost: Dairy/Swine/Poultry






aTotal N = Ammonium-N plus organic N 
Sources: Livestock Waste Facilities Handbook, 2nd ed., 1985, Midwest Plan Service; Organic Soil Amendments and Fertilizers, 1992, Univ. of Calif. #21505.

Legume /green manure

A particular advantage of implementing a legume/green manure rotation into the soil/cropping system is the added source of organic matter. However, green manures also improve soil structure by reducing bulk density. Green manures are generally grown for less than a growing season and are plowed under before producing seeds. Examples of common green manure crops are sunnhemp, annual ryegrass, sudangrass, sudex, and sesbania. Legumes, such as sunnhemp and sudex, are particularly beneficial since they are nitrogen fixing species and are a good source of nitrogen.

Management of organic matter also helps to reduce the occurrence of soil erosion, thus improving soil conservation. In addition to rotations of green manures, cover crops, companion plantings, mulching, and stripcropping with grass species can help minimize the depletion of soil resources, as well as providing a good source of organic residue on the soil surface.

Sewage sludge

  • Sewage sludge consists of the solid products formed during sewage treatment
  • It is not uniform in mineral composition
  • Generally, it contains less than 1 to 3% total nitrogen


Animal manure

  • Animal can contain 0.1 to 0.4% phosphorus.
  • Like nitrogen, the amount of phosphorus in animal manure depends upon several factors, including type of animal feed, handling, and storage of manure.
  • Out of the total amount of phosphorus in fresh manure, approximately 30 to 70% is organic. Thus, mineralization must occur before the organic phosphorus becomes available to plants.

Sewage sludge

  • Sewage sludge contains approximately 2 to 4 % total phosphorus.

Microbial Phosphorus

  • Certain bacteria in the soil are capable of increasing the availability of phosphate, by increasing its solubility.
  • The most abundant P-solubilizer is Bacillus spp.



  • Potassium content may range between 0.2 and 2% in manures.

Sewage sludge

  • Potassium primarily exists as soluble, inorganic K+.


  • Animal manure and Sewage sludge: 0.2-1.5%


  • Animal and municipal wastes: 2-5% (dry)


  • Animal and municipal wastes: 0.2-1.5%


Animal wastes and municipal wastes

Fe: 0.02% – 0.1% (benefit increased chelation)
Zn: 0.01-0.05%, municipal (up to 0.5%) (benefit chelation)
Cu: Animal small (0.002-0.03%), municipal (0,1%) (natural chelation)
Mn: animal (0.01-0.05%) municipal (0.05%) (chelation)
B: animal (0.001-0.005%) municipal (0.01%) (chelation)
Cl: most low because Cl is highly soluble and mobile
Mo: animal (0.0001-0.0005%) municipal (0.0001%)

Distinctions between manure fertilizers and commercial fertilizers

  • Nutrient analysis: While commercial fertilizers may have a relatively high analysis of the major macronutrients (nitrogen, phosphorus and potassium), the nutrient content of manures is much less.
    • As a result, a larger quantity of manure must be applied to the soil as compared to the addition of commercial fertilizer at an equivalent rate. It may take up to 30 tons of manure per acre to achieve the desired nutrition.
  • The nutrient content of manure fertilizers is highly variable.
    • Factors that affect nutrient content include animal type and diet, handling, storage, and water content.
    • Chicken manure generally contains more nitrogen, but also quickly decomposes and subsequently releases ammonia.
    • Since manure is an organic source, the availability of nutrients is also largely influenced by the biological processes of mineralization and immobilization.



  • Provides a source of ammonium
  • Increases the availability of certain essential elements, including phosphorus and various micronutrients
  • Increases the mobility of phosphorus and micronutrients in the soil
  • Increases soil organic matter content
  • Improves water holding capacity
  • Increases water infiltration rates
  • Improves soil structure
  • Reduces aluminum toxicity
  • Recycles nutrients


  • Contains variable nutrient analysis
  • Requires high rates of application due to lower analysis (especially N)
  • Variable quality
  • Undergoes variable rates of mineralization, therefore difficult to predict nutrient availability
  • Less flexibility involved in applying specific nutrient combinations
  • Risk of nitrogen losses volatilization during handling and placement
  • High costs associated with transportation
  • Has relatively low nutrient content per unit weight as compared to mineral fertilizers
  • Potential weed problem through the transfer of weedy seeds which can be minimized through composting

How To Foliar Feed Plumeria

Foliar Feeding

When Dr. Tuckey and his colleagues discovered that plant nutrients could be absorbed through a different part of the plant, besides just the roots, they in turn sparked new testing, new practices and a new debate. Even now, 60 years later, the conversation continues on the effectiveness and benefits of foliar feeding.

The main point of absorption for elemental nutrients is through a plant’s roots. However, sometimes the nutrients can become “locked up” with other elements in the soil, rendering them unusable by the plants. There are many factors that can contribute to nutrients becoming immobile in the soil. If the fertilizer solution you are using is imbalanced or if its pH is too high or too low, the plant may not absorb the nutrients. Poorly managed soils, damaged root-zones, excessive watering: all of these situations can lead to lowered rates of absorption of vital plant nutrients. When a nutrient doesn’t seem to be working effectively through soil applications, using the foliar feeding method is a possible solution.

The leaves, and sometimes even the stems, of many plants are equipped with tiny, pore-like apparatuses called stomata. The word stomata stems from the Greek word ‘stoma,’ meaning mouth. That is essentially how they work. Regulated by task-specific cells, appropriately referred to as “guard cells,” a plant’s stomata will open and close at certain parts of the day. Stomata are essential for two main reasons. The first is to allow oxygen and water vapor to leave the plant (transpiration), which, in turn, cools the plant down and allows for more water and nutrients to flow from the roots to the leaf cells (translocation). The other is to provide a point of entry for carbon dioxide, from the air, to come into the leave and make photosynthesis possible. Stomata can also act as a passage way for getting liquid plant nutrients into a plant. But, as is true with many aspects of life, timing is everything.

The opening and closing of stomata is directly affected by certain environmental conditions. As far as I can tell this is not an exact science yet, but some basic principles seem to be regarded as true. Stomata are generally open during periods of high light intensity. A reason for this could be that the high level of light is causing a high level of photosynthesis and the stomata are open to allow more carbon dioxide in, a fuel for the photosynthesis process. Stomata also open during times of high humidity, when water is plentiful and plants don’t need to worry about conserving. However, stomata remain closed when conditions are exceedingly hot, above 80° Fahrenheit, or very dry. In these conditions, a plant will keep its stomata closed in order to conserve any available water. If you plan on foliar feeding in the hot summer months, it is recommended to feed in the morning or early evening. At these times, the sun is out, but the weather is still relatively cool. Understanding when the window of opportunity is for open stomata to occur is only one part of the picture. The next part is figuring out how to get the nutrients in.

Successful foliar feeding is not as simple as just spraying the liquid on the leaves; it is a process that involves careful technique and a little bit of grace. The following is a small list of tips I’ve compiled to help you along the way.

  • Avoid foliar feeding when temperatures are above 80° Fahrenheit. In the summer, it’s best to spray either in the morning or early evening, when temperatures are lower.
  • If possible, foliar feed when the weather is humid.
  • Check the pH of your nutrient solution before spraying. The ideal pH is right around 7.0, which is referred to as a neutral pH.
  • Mix your solution at a more diluted rate than if you were root feeding. If the directions call for 1 oz. of fertilizer per gallon of water for regular feeding, use 1 tsp per gallon of water when foliar feeding. The smaller the particles are, the more likely they are to enter into the stomata.
  • When spraying the solution, use a sprayer that creates the finest mist possible. This will ensure a better and more even spread of the solution on the leaf.
  • Use a wetting agent or surfactant. Water has a high surface tension rate, causing it to bead up when sprayed. Adding a wetting agent will lower the water’s surface tension, allowing it to thin and spread out.
  • Spray both the tops and bottoms of the leaf, until they are completely covered and excess solution runs off. On most plants, the stomata are on the underside of a leaf, but, at times, they reside on the top. So, just in case, spray both sides.

Possibilities & Realities

A trend that has been occurring in the liquid fertilizer industry for some time now is to market foliar feeding as a simple fix for what may be a major problem. Many companies include language like, “maximizes plant health” or “increases yields” in their literature regarding foliar feeding. I remember reading an advertisement once that said, in so many words, that foliar feeding is effectively the best way to battle bad soils. At that point, I took a step back and thought to myself, is it really?

My feeling is that “bad soils” need to be carefully amended in order to obtain maximum plant growth. However, it is true that foliar feeding can achieve much higher nutrient absorption percentages than root feeding. But it is also true that nutrients absorbed through the stomata do not travel throughout the plant as extensively as nutrients absorbed through the roots do. Also, it is impossible to get significantly large amounts of nutrients through the stomata. Essential elements such as nitrogen (N) and phosphorus (P) are needed by plants in high quantity levels, which are only achievable through root entry. Minor elements, such as iron (Fe) and magnesium (Mg), are needed in smaller amounts that may be obtained through foliar feeding.

If your plant is showing signs of iron deficiency, cut a leaf of the plant and dip half of it in the nutrient solution you plan on using. If, after a few hours, the symptoms begin to subside, go ahead and use the solution on the whole plant. Another element that can become immobile in the soil and may be of benefit in foliar feeding is calcium (Ca). Using calcium in a foliar treatment can help battle blossom end rot in tomatoes and peppers. Foliar feeding can be an effective way of supplying a plant with micronutrients and as a short-term solution to many different nutrient deficiencies. However, if you are experiencing the same nutrient deficiencies on a consistent basis, foliar feeding may not be the answer. Foliar feeding is usually more of a temporary fix, instead of a solution to a problem. This fix can be labor intensive and, at times, can become rather expensive, especially when used on a large scale. I’ve always believed that healthy plants come from healthy soils. Properly amending the soil in your garden should be your first step. Perhaps get your soil tested to see what it is lacking or what there is too much of. If minor nutrient issues arise along the way or if you just want to give your plants a little boost, foliar feeding, when done correctly, can be an effective addition to your gardening repertoire.

Related Images:

Fertilizer Basics

Fertilizer Nutrients

Plumeria need to be fertilized because most soil does not provide the essential nutrients required for optimum growth. Even if you are lucky enough to start with great garden soil, as your plants grow, they absorb nutrients and leave the soil less fertile. Remember those beautiful blooms and leaves you grew last year? It took nutrients from the soil to build those plant tissues. By fertilizing your plumeria, you replenish lost nutrients and ensure that this year’s plumeria have the food they need to flourish.

There are six primary nutrients that plants require. Plants get the first three—carbon, hydrogen and oxygen—from air and water. The other three are nitrogen, phosphorus and potassium.

Nitrogen helps plumeria make the proteins they need to produce new tissues. In nature, nitrogen is often in short supply so plumeria have evolved to take up as much nitrogen as possible, even if it means not taking up other necessary elements. If too much nitrogen is available, the plumeria may grow abundant foliage but not produce flowers. Growth may actually be stunted because the plumeria isn’t absorbing enough of the other elements it needs.

Phosphorus stimulates root growth, helps the plant set buds and flowers, improves vitality and increases seed size. It does this by helping transfer energy from one part of the plumeria to another. To absorb phosphorus, most plumeria require a soil pH of 6.5 to 6.8. Organic matter and the activity of soil organisms also increase the availability of phosphorus.

There are three additional nutrients that plumeria need, but in much smaller amounts: Potassium improves overall vigor of the plumeria. It helps plumeria make carbohydrates and provides disease resistance. It also helps regulate metabolic activities.

Calcium is used by plumeria in cell membranes, at their growing points and to neutralize toxic materials. In addition, calcium improves soil structure and helps bind organic and inorganic particles together.

Magnesium is the only metallic component of chlorophyll. Without it, plumeria can’t process sunlight.

Sulfur is a component of many proteins.

Finally, there are eight elements that plumeria need in tiny amounts. These are called micronutrients and include boron, copper and iron. Healthy soil that is high in organic matter usually contains adequate amounts of each of these micronutrients.

Organic vs. Synthetic

Do plumeria really care where they get their nutrients? Yes, because organic and synthetic fertilizers provide nutrients in different ways. Organic fertilizers are made from naturally occurring mineral deposits and organic material, such as bone or plant meal or composted manure. Synthetic fertilizers are made by chemically processing raw materials.

In general, the nutrients in organic fertilizers are not water-soluble and are released to the plumeria slowly over a period of months or even years. For this reason, organic fertilizers are best applied in the fall so the nutrients will be available in the spring. These organic fertilizers stimulate beneficial soil microorganisms and improve the structure of the soil. Soil microbes play an important role in converting organic fertilizers into soluble nutrients that can be absorbed by your plumeria. In most cases, organic fertilizers and compost will provide all the secondary and micronutrients your plumeria need.

Synthetic fertilizers are water-soluble and can be taken up by the plumeria almost immediately. In fact applying too much synthetic fertilizer can "burn" foliage and damage your plumeria. Synthetic fertilizers give plumeria a quick boost but do little to improve soil texture, stimulate soil life, or improve your soil’s long-term fertility. Because synthetic fertilizers are highly water-soluble, they can also leach out into streams and ponds. Synthetic fertilizers do have some advantages in early spring. Because they are water-soluble, they are available to plumeria even when the soil is still cold and soil microbes are inactive. For this reason, some organically-based fertilizers, such as PHC All-Purpose Fertilizer, also contain small amounts of synthetic fertilizers to ensure the availability of nutrients.

For the long-term health of your garden, feeding your plumeria by building the soil with organic fertilizers and compost is best. This will give you soil that is rich in organic matter and teeming with microbial life.

Foliar Feeding?

Plumeria can absorb nutrients eight to 20 times more efficiently through their leaf surfaces than through their roots. As a result, spraying foliage with liquid nutrients can produce remarkable yields. For best results, spray plants during their critical growth stages such as transplanting time and blooming time.

What About pH?

Even if proper nutrients are present in the soil, some nutrients cannot be absorbed by plumeria if the soil pH is too high or too low. For most plumeria, soil pH should be between 6.0 and 7.0. A soil test will measure the pH of your soil. You can send a sample to a lab (contact your local extension service for a low-cost kit) or buy a home kit and do it yourself. Lime or wood ash can be used to raise pH; sulfur or aluminum sulfate can lower pH. Keep in mind that it’s best to raise or lower soil pH slowly over the course of a year or two. Dramatic adjustments can result in the opposite extreme, which may be worse than what you started with. Once again, a helpful solution is to apply compost. Compost moderates soil pH and is one of the best ways to maintain the 6.5 ideal.

Slow-release, granular Excalibur 11-11-13 or similar fertilizer gives your plumeria all the nutrients they need, including plenty of phosphorus for big, abundant flowers. For a healthy start, mix a handful into the soil at transplant time and at the beginning of your growing season.

How to Choose a Fertilizer

In most cases, an all-purpose, 11-11-13 fertilizer with micronutrients such as Excalibur will provide the nutrients all plumeria need for healthy growth. If a soil test reveals certain nutrient deficiencies, or if you want to tailor your fertilizer to the needs of particular plumeria, you can select a special formulation. What you choose will depend on your soil and what you are growing.

The three numbers that you see on a fertilizer label, such as 11-11-13, tell you what proportion of each macronutrient the fertilizer contains. The first number is always nitrogen (N), the second is phosphorus (P) and the third is potassium (K). This "N-P-K" ratio reflects the available nutrients —by weight—contained in that fertilizer. For example, if a 100-pound bag of fertilizer has an N-P-K ratio of 11-11-13, it contains 11 pounds of nitrate, 11 pounds of phosphate (which contains phosphorus), 13 pounds of potash (which contains potassium) and 84 pounds of filler.

Note that the N-P-K ratio of organic fertilizers is typically lower than that of a synthetic fertilizer. This is because by law, the ratio can only express nutrients that are immediately available. Most organic fertilizers contain slow-release nutrients that will become available over time. They also contain many trace elements that might not be supplied by synthetic fertilizers.

To build the long-term health and fertility of your soil, we recommend using granular slow release fertilizers with micronutrients. Supplemented with a water-soluble fertilizer ensures that your plants have the nutrients they need when they’re in active growth.

Potassium (K)

Potassium is a chemical element with symbol K (derived from Neo-Latin kalium) and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction and burning with a lilac flame. Naturally occurring potassium is composed of three isotopes, one of which, 40K, is radioactive. Traces (0.012%) of this isotope are found in all potassium making it the most common radioactive element in the human body and in many biological materials, as well as in common building substances such as concrete.


Because potassium and sodium are chemically very similar, their salts were not at first differentiated. The existence of multiple elements in their salts was suspected in 1702, and this was proven in 1807 when potassium and sodium were individually isolated from different salts by electrolysis. Potassium in nature occurs only in ionic salts. As such, it is found dissolved in seawater (which is 0.04% potassium by weight), and is part of many minerals.

Most industrial chemical applications of potassium employ the relatively high solubility in water of potassium compounds, such as potassium soaps. Potassium metal has only a few special applications, being replaced in most chemical reactions with sodium metal.

The Role of Potassium (K)

Potassium is a chemical element with symbol K (derived from Neo-Latin, kalium) and atomic number 19. It was first isolated from potash, the ashes of plants, from which its name derives.

Phosphorus (P) Fallacies

A brief review of the macronutrients included in complete fertilizers: nitrogen (N) is involved in photosynthesis as part of the chlorophyll molecule and promotes vegetative growth; phosphorus (P) supports the transfer of energy throughout the plant for root development and flowering; and potassium (K) is an important part of plant metabolism, strengthening its overall health.

Too Much Nitrogen in Plumeria

Nitrogen is a key player in producing chlorophyll; this pigment absorbs sunlight for basic photosynthesis needs. Gardeners must make sure that nitrogen, one of the three macronutrients in soil, is available for root uptake by choosing the right fertilizer. Saturating a garden with high nitrogen levels, however, does not improve plant growth. In fact, it can actually harm a garden more than leaving it to its natural elemental state. Too much nitrogen in plants is apparent both above and below the topsoil.