Understanding Fertilizers

Understanding Fertilizers by Tex Norwood

I’ve always been interested in developing a better fertilizer to use on plumeria and I love research and experimenting. After I started growing Plumeria it was only natural from me to start experimenting with different fertilizers, soil mixes and nutrients. After years of experimenting and not coming up with what I wanted, I began to look into custom mixes, but soon realized they required investing even more time and money.

After joining Florida Colors Nursery in 2012, what seemed to be a daunting to impossible task became a necessity. The task of developing a custom fertilizer mix was necessary to provide the best possible care for our 14,000 plus plumeria plants. Our goal was to develop a fertilizer designed specifically for plumeria for our own use and to reduce the work load of applying it.

We spent over a year researching and meeting with fertilizer companies. Frustrated and beginning to wonder if we were just dreaming, we finally found a company with quality ingredients, the experience and willingness to produce a quality custom blend to our specifications. The blend turned out to be a slow moisture activated fertilizer that lasted 9 months, releasing specific nutrients as our plumeria growth habits dictated. After field testing, we decided to share it with our customers and Excalibur Plumeria Fertilizer was born. Needless to say, it has exceeded our expectations.

The follow information is a summary of conclusions to help you provide what your plumeria needs to grow healthy and bloom the way they should.

Plumeria Fertilization & Nutrition

Fertilization is one of the most important aspects of plumeria care. All plumeria require nutrients to survive and grow. The quantity of nutrients available to the Plumeria is affected by soil quality and water quality.

Plumeria require micro and macro nutrients for good health. Whether you’re planting a delicate young seedling or tending a mature plumeria, the health of the roots is of utmost concern for its future growth. Plumeria trees are often surviving in soils that do not contain enough available nutrients for satisfactory growth and development. Fertilizers and soil amendments help to alleviate some of the stress caused by the environment and severe weather conditions.

There are two sorts of mineral nutrients: Macronutrients, are required in large quantities and Micronutrients, are required in small quantities. The big three macronutrients, nitrogen (N), phosphorus (P) and potassium (K), together comprise over 75% of the mineral nutrients found in Plumeria. Calcium (Ca), Magnesium (Mg) and Sulphur (S) are also macronutrients required in smaller quantities. Micronutrients are required in very small quantities are Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B) and Chlorine (Ci). All nutrients are abbreviated by one or two letters, their chemical symbols that are based on their Latin names. The symbols are the same in all languages.

Plumeria get nutrients from the air, the soil and the water. Plumeria use photosynthesis to convert light energy into chemical energy stored in carbohydrate molecules, such as sugars, which are synthesized from carbon dioxide and water.

It is important for plumeria to receive at least six hours of direct sunlight every day for them to be healthy and properly produce blooms. Three to four hours is not enough. Bright, indirect sunlight also counts but contributes significantly less energy to the plant than direct sunlight. Sugars and carbohydrates are combined with nutrients to produce protein, enzymes, vitamins and other elements essential to plumeria growth.

Nutrients are taken up by the fine root hairs, not by the big roots. Even the very largest of trees have many small, fine root hairs to absorb the nutrients and water they need. The larger roots are used for supporting the tree and for storage of water and other Plumeria food. The root hairs can also excrete liquids that affect the acidity of the soil (pH). When the pH changes, the amount of nutrients available may also change.

Why is the pH important?

Substrate pH is a measure of the acidity and alkalinity in soils. pH levels range from 0 to 14, with 7 being neutral, below 7 acidic and above 7 alkaline. The optimal pH range for most plumeria is between 6.5 and 7.0; however, many plumeria have adapted to thrive at pH values outside this range. Because pH levels control many chemical processes that take place in the substrate, specifically, plant nutrient availability, it’s vital to maintain proper levels for your plumeria to reach their full bloom potential.

What is considered a balanced diet of fertilizer and nutrients?

All 3 non-mineral nutrients hydrogen (H), oxygen (O) and carbon (C) and all 13 mineral nutrients are needed for healthy plumeria growth in the correct amounts, and the three mineral nutrients needed in the largest amounts are nitrogen (N), phosphorus (P) and potassium (K). These are the three numbers on fertilizer containers and are often abbreviated NPK.

This is confusing, because different people use the word “balance” differently when discussing nutrient management. I have seen articles that suggested using a “balanced” fertilizer that has equal amounts of the three macronutrients: nitrogen (N), phosphate (P), and potash (K).

To me, a “balanced diet” for plumeria means a fertilizer or combination of fertilizers and soil amendments that provides nitrogen, phosphate, potash and micronutrients in the ratios that the plumeria needs when they need them.

Nitrogen is important for leafy growth and energy production, phosphorus is key for the storage and transfer of energy, and potassium is essential for many aspects of metabolism. Nitrogen is water soluble and that which is not used by plants may be leached from the soil. Phosphorus is tightly bound by soil particles and remains in place unless used by the plant or is washed into gutters and streams. Potassium is bound to soil less tightly than phosphorus and potassium excesses are not usually harmful.

Plumeria need all 13 mineral nutrients to remain healthyIf one is missing, your plumeria will not grow well. It is easy to confuse the symptoms of nutrient deficiencies with those of too much or not enough shade or water. In fact, all three factors, shade, water and nutrients affect your plumeria growth, and interact to produce a healthy plumeria. Plumeria that grow in full light with abundant moisture and receives all the 13 mineral nutrients will grow normally, have healthy green leaves and bloom normally. Together, water, sun and nutrients must be monitored and adjusted with the weather to produce a healthy plan.

Do my plumeria need a lot of phosphorus to produce more blossoms? 

In a word, no. The effect of phosphorus on a plant’s metabolism and the amount needed by all plumeria is greatly misunderstood and misstated.

Well-qualified horticulturists have reviewed the status of phosphorus as it relates to plant function and have stated there is no scientific evidence that excessive phosphorus is needed by plants for any reason. There is no evidence that excesses have any beneficial effect on blooming or healthy roots of plants in general, in fact, too much appears to be harmful.

No doubt all plants need phosphorus for normal function. Typically, USDA soil tests will show adequate or more often excessive amounts of phosphorus. The excess of phosphorus has several undesirable effects. It has been shown to interfere with a plant’s absorption of iron, manganese and zinc, resulting in yellowing of leaves and poor health of the plant. Excesses may also interfere with the growth of beneficial fungi, called mycorrhizae. These fungi are normally present on most plant roots and assist the plant in absorbing water and nutrients. Without these fungi, plants must work harder than they would otherwise.

It takes practice to learn the signs identifying a missing nutrient or nutrients, but you can learn to do so, and some of the signs are common. A good practice is to carefully monitor the leaves of your plumeria for signs of nutrient deficiency and correct them with a better soil mix or with fertilizer.

Types of Fertilizers

Fertilizers are organic or inorganic. Organic fertilizers contain only plant or animal-based materials that are either a byproduct of naturally occurring processes, such as manures, leaves, and compost. Inorganic fertilizers also referred to as synthetic fertilizers, are manufactured artificially and contains minerals or synthetic chemicals. Inorganic fertilizers contain only nutrients; they are not used to combat Plumeria diseases or insects. Inorganic fertilizers do not improve the soil’s physical properties, whereas organic material such as compost does.

Granular fertilizers commonly have the NPK in the names such as “11-11-13”, or “6-12-6”. The numbers represent the percentages of nitrogen (N), phosphorus (P), and potassium (K) in the fertilizer — 11% N, 11% P, 13% K. In this case, 34% of the mixture is made up of N-P-K, and the rest is inactive material used to help spread the fertilizer evenly or coating to extend the application rate.

Granular fertilizers are typically mixed into the potting mix, dissolved into the irrigation water or be applied on the soil surface. It is better to mix the fertilizer directly into the potting mix before planting or in the top few inches of soil, because the roots can avoid or seek the fertilizer as they need it. It is better to add too little then too much. When applying fertilizer think about the size of your root system. A mature plumeria root system will need more fertilizer and a young seedling will need less fertilizer. Plumeria typically respond to granular fertilizers within two weeks.

Foliar fertilizers are used in order to get the nutrients to the Plumeria quickly. They are specially formulated to apply directly on the leaves and be absorbed by the leaves, not by the roots. When Plumeria are acutely deficient in nutrients, foliar fertilizers often help ‘green them up’. Frequently, foliar fertilizers will only contain the micronutrients, since it is assumed that the macronutrients are available in the soil. 

Because foliar fertilizers are expensive, a short-term solution and they do not encourage strong root growth, they should be used in combination with granular fertilizers for a long-term solution.

When do Plumeria need nutrients?

Plumeria need nutrients most in the spring and summer during their most vigorous growing and need less and less as they slow down and start going into dormancy. Growth virtually ceases for winter in non-tropical regions when they need no water and no nutrients.

Dormancy is the state in which a plumeria exhibits little or no growth and in which most, if not all, metabolic activity ceases or slows down for a period of time. Dormancy evolved as a means of surviving unfavorable environmental conditions such as short days, cold temps and or drought.

Dormancy levels vary between by plumeria locations. In general, the number of plumeria that may acquire dormancy shows a trend to increase with geographical distance from the equator and correlates with the occurrence of seasons. Variation can also be found within different plumeria varieties.

I hope this information makes it easier to choose the right fertilizer and nutrients for your plumeria.

Common nutrient deficiency symptoms

Macronutrients

Nitrogen: This is a mobile nutrient, which means that when nitrogen is deficient, Plumeria move it from the older foliage to the younger, actively growing leaves. The older leaves (the ones lower on the stem of the tree) become yellow first, while the new leaves remain green.

Phosphorus: The entire plumeria is stunted, especially during early growth. Too much Phosphorus will not allow the fine roots to grow and take up nutrients. Depending on the cultivar, the leaves may become dull green, yellow or purple-tinged. The purpling of leaves is a classic symptom, but sometimes there are no color differences in leaves, so visual diagnosis is not always reliable. The purple color should not be confused with new leaves that often appear purple or red when they first flush out.

Potassium: Symptoms appear in older leaves first. These start to yellow at the edges and have some green at the base. Later, leaf edges turn brown and may crinkle or curl and small necrotic (dead) spots may appear. Plumeria may wilt, even though sufficient water is available in the substrate. When deficiencies are severe, leaves will die.

Calcium: This is difficult to detect because signs include slow growth and die-back of bud or root tips. Seedlings will have stubby little roots with brownish discoloration. The problem is most common in very acidic soils. A well-developed root system with many fine root hairs is important for calcium uptake.

Magnesium: This nutrient is commonly deficient in coarse-structured soils and in acidic soils. Uptake may be blocked if there is too much potassium in the soil. Like nitrogen, magnesium is a mobile nutrient, so deficiency symptoms show up in the older leaves first. These leaves show a very characteristic yellowing between the veins or ribs, and they appear streaked.

Sulphur: Plumeria will be slightly stunted. This is not a mobile nutrient, so the symptoms show up on younger leaves which are initially light green, but eventually develop scorched and curled margins. Dry areas can form along the margins and then spread inward to the leaf midrib.

Some Common nutrient deficiency symptoms

Micronutrients

Micronutrient deficiencies are difficult to diagnose because often more than one nutrient is missing. Only the most common symptoms are listed below.

Iron: Deficiency is common on alkaline or calcareous soil (pH above 7). Younger leaves become yellow to white and dry up.

Manganese: The tissue between the vein’s mottles, while the veins remain green and are surrounded by a band of green tissue.

Copper: New leaves are yellow at the tips and often become twisted.

Boron: The deficiency affects the terminal bud which yellows, dries out and dies. Plumeria grow slowly.

Plumeria require 13 nutrients in different quantities to grow well. Common deficiency symptoms help identify which nutrients are missing. Nutrient deficiencies should not be confused with the effects of too much or too little shade and water.