What Happened to My Plants
January/February 1998 African Violet Magazine, pgs 43-45
By Dr. Charles Cole
Providing good nutrition for our African violet plants involves more than purchasing a fertilizer product and applying it to the plants. We need a basic knowledge of what a plant needs and how a specific nutrient effects a plant under a given set of conditions. If we understand how to use specific fertilizer elements we may use them to obtain a desired response from our plants. A familiar example of this is seen when we reduce the use of nitrogen in our fertilization program in an effort to enhance variegation in certain cultivars.
There are 16 chemical elements which are essential for plant growth. Often we see them grouped into two groups, the non- mineral elements and the mineral elements.
The 3 non-mineral elements are Carbon (C), Hydrogen (H), and Oxygen (0). These elements are obtained from water and from the air. They are utilized in the form of H20, water and C02, Carbon dioxide, in the process of photosynthesis. A deficiency of carbon dioxide, water or light can result in reduced growth but may produce no other visible symptoms.
The 13 mineral elements essential for normal plant growth are absorbed from the soil (potting media). These elements are divided into 3 groups; the primary nutrients, the secondary nutrients and the micronutrient.
Primary Nutrients are often called the fertilizer nutrients. They consist of Nitrogen (N), Phosphorus (P) and Potassium (K). The percentages reported on many commercial fertilizer containers refer to these nutrients. For example, 5-10-5 refers to the percent of N, P & K respectively in the product.
Secondary Nutrients are often deficient in soils but not nearly so often as the primary nutrients. These nutrients are: Calcium (Ca), Magnesium (Mg) & Sulfur (5). These nutrients are utilized in many processes which takes place in the plant and deficiencies seriously effect plant health.
Micronutrient are often called minor elements or trace elements. Many commercial products have one or more of these elements added. Micronutrient included; Mn - Manganese, Iron (Fe), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo) and Chlorine (Cl).
Although essential in trace amounts these micronutrient in excess amounts can be toxic to plants, resulting in damage to the plants which is as serious or more serious than if they occurred in deficient amounts.
The availability and utilization of all plant nutrients are affected by water, temperature, light and pH.
In general water which is often called the universal solvent is necessary for dissolution and transport of nutrients throughout the plant system and for the completion of many of the continuous processes which go on within a plant. Temperature, within its tolerant range regulates the speed of reactions within a plant; initiating some reactions, speeding up reactions, slowing reaction and stopping some reactions. Light acts as a power source, also effecting reactions.
These 3 factors have been discussed in detail in a previous article in the AVSA Magazine (Vol. 50, No. 6, pp 12-14).
The pH is a measure of the acidity or alkalinity of a substance; soil, water, etc. It is measured on a scale of from 0 -14. A pH of 7 is neutral. A pH above 7 is alkaline, like ammonia and a pH below 7 is acid, like vinegar.
When soil particles are saturated with ions of calcium, magnesium, potassium or sodium it has a high pH and is said to be basic or alkaline. These soils are often referred to as 'sweet' soils. When these ions are replaced with hydrogen ions the soil has a low pH and is said to be acid. These soils are often referred to as 'sour' soils. Leaching is a common cause of sour soils, as the ions creating a high pH are leached out and are replaced with H ions.
The pH of the media in which plants are grown can greatly affect their health. The pH plays an important role in determining which nutrients are available and in what amounts.
This is especially true in the case of K, C, Mg and S. Nutrients can either be tied up and unviable or released in toxic amounts, depending upon the pH.
The most favorable pH for nutrient uptake by plants ranges from 6.3 - 6.7. However, certain plants prefer more acid conditions while others thrive in higher alkaline conditions. African violets prefer a pH of 6.5-6.7.
It is extremely difficult to induce nutrient deficiency symptoms in the African Violet. Research has shown that you may grow AV's in sterile soil for 18-24 mos. and still show no symptoms and a specific nutrient deficiency.
The African violet stores nutrients in its stems, petioles and leaves. This makes the plant a very well buffered system which is capable of 'borrowing' nutrients from one part of the plant to feed another part. This movement of nutrients and 'food' from one part of the plant to another is known as translocation. Seldom do symptoms of nutrient deficiencies appear in AV's while the deficiency occurs, however symptoms may occur much later, sometimes even after the problem has been corrected.
When we fertilize African violets we put nutrients into the soil not plant food. African violets, like other plants, manufacture their own food. Nutrients are taken up by the roots and transported to the leaves. Here in the presence of light, using chlorophyll as a catalyst the nutrients are, through the process of photosynthesis, manufactured into amino acids, proteins, starches, sugar, carbohydrates and other products that plants use as food for plant growth and development. The products of photosynthesis, plant food, is then translocated to other areas of the plant where they are used by the plant or stored for future use.
The soil or potting media in which plants grow serves as a pantry to accumulate and store nutrients for use by plants.
Of all of the essential nutrient elements only Nitrogen moves freely through the soil in the form of nitrates. Nitrogen is readily water soluble and can travel anywhere water can go. The other nutrients move little to none and are available only where plant roots reach them. The availability of nutrients in the soil is effected by temperature and soil pH.
Nitrogen is abundantly available in nature but not in a form available to plants. Plants take up N in the form of nitrate salts and ammonium salts. These are converted into amino acids. Amino acids are combined to form proteins. Proteins are used to build plant tissues.
Nitrogen is often referred to as the 'foliage' nutrient. Fertilizing a plant deficient in N often results in a quick spurt of plant growth and an intensification of the green color as N is found in the chlorophyll molecule which gives a plant its green color.
A deficiency in N produces a condition called chlorosis. This is manifest in a loss of green color and the plants appear 'yellowed' or faded in color. The older leaves of a plant are the first affected because nitrogen, is translocated from older tissue to the younger actively growing tissue in the crown of a plant, leaving the older leaves deficient in the element.
Phosphorus is necessary for the utilization of energy in plant metabolism. It is necessary for the photosynthetic reaction which transforms the energy of light into carbohydrates. Phosphorus is essential for proper cell division. A deficiency in P results in reduced growth, thin stalks, small leaves and in severe deficiencies a stunned growth.
A deficiency in P often results in a reddish, purplish or brown color developing in plant leaves, especially along the leaf veins. Phosphorus is often referred to as the 'root' nutrient and is often applied to give the root system of young plants a boost.
Potassium is needed for protein and carbohydrate formulation. Potassium activates specific enzymes in a plant and regulates a number of chemical reactions necessary for
metabolism and growth. Potassium enhances the plant's ability to resist disease, cold temperature and other adverse conditions.
Plants deficient in K may show a dark green or blue- green color. Necrotic (dead) spots may occur on leaves or along the leaf margin. Plant growth is slowed under severe conditions. Blossom and seed formulation can be affected.
Symptoms will appear on the older leaves first as K is translocated from the older to the younger leaves.
Potassium is often referred to as the blossom or seed nutrient.
Calcium is a component of the cell wall. It is necessary for cell division and elongation. Calcium acts as a cement to hold cell walls together and to hold one cell to another, building tissue.
As Ca is not translocated in appreciable amounts, symptoms are found first and most severely in the youngest leaves or crown of a plant. In severe deficiencies the growing part of plants may die. Plants deficient in Ca may have very poor root growth and damaged roots making them very susceptible to infection by bacteria and fungi.
A delicate balance in Ca is necessary in plants. A deficiency may create a toxicity of aluminum, boron, magnesium or potassium.
Magnesium is the key element in the chlorophyll molecule. It is often called the 'companion for phosphorous' as the two combine, facilitating their movement to their proper site in a plant for utilization. Magnesium is necessary for amino acid and fat synthesis. It also affects the viability of seeds.
Magnesium is readily translocated so symptoms will be found in the oldest leaves first. Deficient plants may show marginal chlorosis or chlorosis may appear as yellowish blotches on a leaf. Damaged leaves often show a yellow, orange or red pigmentation.
Sulfur is needed for the formation of new cells and chlorophyll. Sulfur is a component of certain amino acids which are found in most protein molecules.
Symptoms of S deficiency appear much like those of N. deficiency. Plants are chlorotic, spindly and grown poorly.
Iron, although needed in very small amounts, is most essential to the health of plants. Iron functions as a catalyst in the formation of chlorophyll. It also acts as an oxygen carrier within the plant. In acid conditions iron is readily available but under alkaline conditions iron is held in a form not available to most plants.
Deficient plants show symptoms in the youngest tissue first, as iron is not readily translocated within the plant.
The first signs of a deficiency appears as a pale green color of the tissue between the leaf veins while the veins themselves remain green. Under severe deficiency entire leaves or even an entire plant will become yellow to almost white and the leaves may begin to die from the tip back.
Manganese activates enzymes involved in chlorophyll formation. Symptoms appear in the youngest leaves first and look much like iron deficiency with yellowing between the leaf veins. Sometimes brownish or blackish spots may occur along a leaf. The tissue in the spots may eventually die causing dead spots or streaks between leaf veins.
Zinc deficiency may cause conditions called 'little leaf' and 'rosette'. These conditions are the result of abnormal tissue growth. Leaves may become twisted and may have necrotic spots within the leaf.
Copper deficient plants often have leaves which are dark green in color and have their margins rolled up. Flowering and fruiting are curtailed.
Boron deficiency may be seen as damaged plant terminals. Tissue may appear hard, dry and brittle. Leaves may become distorted and the stems may be rough and cracked: Corky ridges or spots may appear on the plant stem.
Molybdenum deficiency will appear as a chlorosis between leaf veins. Leaves often appear mottled and their margins tend to curl or roll up.
Chlorine deficiencies apparently do not occur naturally. Only artificially induced deficiencies have been observed in plants.
When all of the above information has been digested you may want to go to the following key to plant-nutrient deficiencies and try your hand at identifying some plant- nutrient problems.
To use this key read 1 a and l b. Observe your problem plant and see which of the statements your plant fits. Then proceed to the next couplet of statements as directed by your choice (1 a or 1 b). Continue in this manner until a statement indicates the specific nutrient responsible for your set of plant symptoms.
Key to Plant-Nutrient Deficiencies
lb. Problem effect is localized on younger (terminal) leaves or plant.....6
2a. Problem effect general on entire plant; lower leaves shows yellowing and drying up (firing). Acute stages develop reddish to purplish color on lower leaves.....3
2b. Problem effects localized, appears as a loss of green color or mottling (chlorosis). May have dead (necrotic) spots on lower leaves. Very little if any drying-up of lower leaves.....4
3a. Color is faded, beginning with tips and margins of leaflets until all foliage becomes a lighter green than normal. Over time, the color may fade to pale yellow. In extreme cases margins of lower leaves become devoid of chlorophyll and curl, sometimes the leaves will 'fire-up'. Stunted growth and defoliation are characteristics of prolonged problems.....Nitrogen
3b. Foliage crinkly and dark green. In acute cases lower leaves become purplish. Plants stand stiffly erect. Leaflets, leaf margins and petioles take an upward direction. Leaflets are often cup-shaped. Leaves fail to expand to normal size. With acute deficiency growth is seriously affected.....Phosphorus
4a. Foliage darker green than normal. Leaf reduced in size. Internodes short. Plants have a humped-up, recurved appearance. Foliage becomes crinkled and veins become sunken. If prolonged the deficiency causes a slight yellowing of the leaves, then a bronzing develops from the tips of the plant. Plants become weakened and are more susceptible to disease organisms....Potassium
4b. Lower leaves lighter green than normal....5
5a. Chlorosis begins at tips and margin of leaves and progresses between the veins toward the center of the leaflet. If prolonged the tissue between the veins is filled with brown and dead areas. A definite bulging between veins and thickening of the leaves occurs. Effected leaves are brittle.....Magnesium
5b. The lower leaves are chlorotic and may develop grayish-brown to bronze irregular spots. This usually occurs first on leaves mid way into the center of the plant (midway up the stem) but will eventually affect most of the plant. Spots become sunken and the tissue eventually dies. Leaves may be small, thick. Spots may develop on leaf petioles and stem. Margins of leaves may curl upward....Zinc
6a. Unusual distortions at the tips or bases of young leaves making up the terminal bud. Terminal bud dies.....7
6b. Terminal bud remains alive. Chlorosis occurs on newer leaves. Chlorotic leaves may have spots of dead tissue. Veins light to dark green.....8
7. The young leaves of the terminal bud are lighter green than normal. The lighter color is more pronounced at the base of the leaves. Stem tip may die or have distorted growth. Leaves become thickened and curl upward. The leafstalks become brittle. Purple coloration may develop. Tips and margins of leaves (especially lower leaves) die prematurely.....Boron
8a. No pronounced general or uniform yellowing of the leaves.....9
8b. If chlorosis is present it is only slight and uniform through out the leaf.....10
9a. No pronounced chlorosis. Young leaves become limp and remain permanently wilted. Terminal leaves wilt as flower buds are being produced. Tips of leaves dry up and turn brown if deficiency persists.....Copper
9b. If leaves turn yellow it is a slight, general yellowing similar to nitrogen deficiency and leaves do not dry up. Growth is stunted. Some spotting of leaves occurs in advanced stages of deficiency.....Sulfur
10a. A slight uniform chlorosis on young leaves. Tips and margins of leaves remain green longest. Principle veins retain normal green color. Tissue gradually becomes pale yellow, almost white in extreme cases. No dead spots are found in leaves.....Iron
10b. Leaves become lighter green than normal between the leaf veins. This is most pronounced in the center of the plant. These areas may become yellow to white in severe cases and may develop small brown spots. The outer leaves are the last to be affected.....Manganese