Basic Plant NUTRITION
Dr. Ryan Lee, PhD
Symptoms of Nutrient Deficiency and Excess
An understanding of basic plant nutrition is recommended for those with a serious interest in gardening. The purpose of this article is to explain the function of the essential nutrients in plants and to provide information about recognizable symptoms in plant material when there is a nutrient deficiency or excess. Following diagnosis it may be possible to improve plant health and vitality by adjusting nutrient levels.
Click on a nutrient box to learn more about the most
commonly associated plant symptoms
Primary NutrientsN Nitrogen P Phosphorus K Potassium
Secondary NutrientsCa Calcium Mg Magnesium S Sulfur
NUTRIENTS MUST BE “PLANT AVAILABLE”
All of the nutrients listed here are essential - plants cannot live without even the least of these. It is not enough that the nutrients are present – they also must be “plant available”. Availability depends largely on soil texture, organic matter, and pH. Therefore it is highly recommended that gardeners start their nutritional program with a high-quality soil test from a reputable testing facility. While Osmocote® Plant Food, the sponsor of this website, provides several essential nutrients and / or brings the concentration of certain nutrients to levels that are available to the plant, its ability to do so is dependent on the soil’s characteristics.
WHERE DEFICIENT/EXCESS NUTRITION FIRST APPEARS IN A PLANT MATTERS
A key concept in understanding plant nutrition is “mobility”. For example, Nitrogen is a very mobile nutrient. When the soil is lacking sufficiently available Nitrogen, a plant will rob available Nitrogen from its old leaf material and move it into actively growing points (from source to sink). Therefore, the deficiency develops on the old leaves first. They turn yellow between the veins as the Nitrogen is wicked out of the cells towards the needy, new growth. Calcium on the other hand, is immobile. Therefore, if a plant finds itself in an environment that has low available Calcium, the symptoms will most likely manifest in the newest growth, as the plant is unable to shunt this nutrient easily. Plants deficient in Calcium will display irregular growth in the newest leaves.
UNDERSTANDING BASIC PLANT PHYSIOLOGY IS KEY IN DIAGNOSIS
From the two examples above concerning Nitrogen and Calcium it is easy to see that diagnosing nutrient deficiency (or excess) requires not only characterizing the symptom but also understanding some basic plant nutrition physiology. If symptoms develop on the old growth, the nutrient is mobile. If symptoms develop on new growth, you are likely dealing with an immobile nutrient. Armed with this knowledge and a good soil test, any gardener should be able to diagnose nutrient related diseases.
DIFFERENCE BETWEEN PLANT ESSENTIALS AND “BENEFICIALS”
Before turning to the review of specific nutrients, there is another category of materials that gardeners give to their plants. Let’s call them “beneficials”, that is, things that might improve plant growth but are not required (things like giving sugar water to a pumpkin). As interesting and helpful as such things may be, they are not essential to plant life and are not reviewed in this article.
PRIMARY NUTRIENT DEFICIENCY AND EXCESS SYMPTOMS IN PLANTS
FUNCTION OF NITROGEN IN PLANTS
Plant uptake of Nitrogen depends upon its chemical form. For example, while the atmosphere is comprised largely of Nitrogen, gaseous Nitrogen is not available to plants unless it has been converted into an inorganic form by microorganisms in the soil. Nitrogen is the most heavily used nutrient thus it tends to be the most limiting nutrient. In addition, there is competition for this nutrient in the soil from both plants and microbes. The addition of Nitrogen tends to give the greatest response of any single nutrient. For that reason Nitrogen is often the most over-applied nutrient. Gardeners wish to see “big, healthy, green” plants. But, there can be too much of a good thing. Excess levels of Nitrogen in grasses like corn, wheat, rye, etc. will lead to lodging (i.e., falling over). Excess Nitrogen in tomatoes, cucumbers, melons and squash, will drive excessive vine growth at the expense of fruiting. Since Nitrogen is highly mobile, it is susceptible to being washed through the soil column if not taken up by plants. Ultimately this free Nitrogen ends up in bodies of water where it upsets the ecosystem causing algal blooms and subsequent fish-kills. It is important to apply only the necessary amount of fertilizer to your gardens. The amount of Nitrogen required depends on the plant species. For example, starches like potatoes and corn are heavy feeders and can benefit from higher Nitrogen levels whereas trees and shrubs can thrive with lower Nitrogen concentrations.
GENERAL SYMPTOMS OF NITROGEN DEFICIENCY IN PLANTS
(Nitrogen is mobile so symptoms show on old leaves first):
Appearance of leaves:
- Uniformly yellow-green
- Early drop in fall
- Increase in occurrences of disease
Shoots may be:
- Short and small in diameter
- Overly reddish or reddish brown (in some plants)
Flowers and Fruits may show:
- Delayed bloom, early maturity
- Undersized blossoms or fruit
GENERAL SYMPTOMS OF NITROGEN EXCESS IN PLANTS
Symptoms include absence of fruits / flowers accompanied by an abundance of leaves with weak stems. Over-feeding of Nitrogen makes the plant more susceptible to diseases and pests.
FUNCTION OF PHOSPHORUS IN PLANTS
Phosphorus is necessary for seed germination and root development. Deficiencies most likely occur in where the soil has little organic material. Phosphorus is less available in cooler soil temperatures therefore the deficiency may manifest during a cold spring and disappear when the soil warms. Symptoms of Phosphorus deficiency may be difficult to diagnose because other factors may yield similar symptoms. Phosphorus is mobile so old leaves turn purple first.
GENERAL SYMPTOMS OF PHOSPHORUS DEFICIENCY IN PLANTS
- Red or purple leaves
- Purplish lower stems
- Poor root development
- Loss or absence of lower leaves
- Stunting and delayed maturity
- Reduced flowering
GENERAL SYMPTOMS OF PHOSPHORUS EXCESS IN PLANTS
Too much Phosphorus can suppress the uptake of micronutrients such as Iron and Zinc. An overabundance of Phosphorus can also interfere with Nitrogen absorption.
FUNCTION OF POTASSIUM/POTASH IN PLANTS
Potassium is absorbed in larger quantities than any nutrient other than Nitrogen. It supports photosynthesis. It also increases drought tolerance by reducing water loss in leaves. Potassium deficiencies can occur in new gardens and/or sandy soils low in organic matter. The classic Potassium deficiency symptom is “burnt edges”. Leaf margins look like they have been scorched. Potassium is mobile so the symptom shows up on the old leaves first.
GENERAL SYMPTOMS OF POTASSIUM/POTASH DEFICIENCY IN PLANTS
- Chlorosis (yellowing) between leaf veins
- Brown spots or yellowing edges on leaves
- Scorching and curling of leaf tips
- Older leaves will be affected first
- Reduced plant growth and root development
- Small, poorly colored fruit
GENERAL SYMPTOMS OF POTASSIUM/POTASH EXCESS IN PLANTS
When plants get too much Potassium, the absorption of other nutrients is inhibited. That’s why the condition is so difficult to diagnose. Excess potash may also lead to elevated levels of salt.
SECONDARY NUTRIENT DEFICIENCY AND EXCESS SYMPTOMS IN PLANTS
FUNCTION OF CALCIUM IN PLANTS
Calcium is an essential ingredient in cellular structure. It is important in both leaf and root development. Calcium does not migrate easily from older to younger tissue so look for symptoms at the growing points. Leaves may be distorted and brown with curled tips. Malformation is the classic Calcium symptom.
GENERAL SYMPTOMS OF CALCIUM DEFICIENCY IN PLANTS
- Brown leaves or bleaching of leaves
- Deformed growth (twisting and bending)
- Reduced plant height
- Poorly developed roots
- Poor fruit development
- Cracking in tomatoes; brown heart in leafy vegetables
GENERAL SYMPTOMS OF CALCIUM EXCESS IN PLANTS
Calcium excess may cause deficiencies in Magnesium and Potassium. It can prevent the germination of seeds and reduce plant growth.
FUNCTION OF MAGNESIUM IN PLANTS
Magnesium is essential for photosynthesis and is an important part of chlorophyll. It also participates in many enzyme activities. Magnesium is often deficient within sandy soils as may be found in coastal areas due to low levels of organic material. It may also occur where high levels of N and K have been applied. Magnesium deficiency is commonly associated with yellowing leaves. It is most often visible during wet and cold periods. Over-watering a plant can look like Magnesium deficiency.
GENERAL SYMPTOMS OF MAGNESIUM DEFICIENCY IN PLANTS
- Yellowing leaves
- Curling leaves (downward or upward)
- Premature shedding of leaves
- Early dropping of Immature fruit
- In conifers, orange-colored needles
GENERAL SYMPTOMS OF MAGNESIUM EXCESS IN PLANTS
Too much Magnesium may cause deficiencies in other nutrients, such as Calcium and Potassium.
FUNCTION OF SULFUR IN PLANTS
Though Sulfur is rarely deficient, when the condition does occur, it will probably be where the soil is sandy or where the level of organic material is especially low. Sulfur plays a variety of roles in plant life but is generally associated with chlorophyll formation. It also enhances root growth, seed production and the plant’s ability to withstand cold. Sulfur deficiency is most likely visible in leaves. Plant available Sulfur comes from microbial activity breaking down organic material and from acid rain. As control of pollution improves, horticulturalists are beginning to see Sulfur deficiencies in production fields. A word of caution, soil Sulfur is an acid. Addition of this nutrient will likely decrease soil pH.
GENERAL SYMPTOMS OF SULFUR DEFICIENCY IN PLANTS
- Yellowing of young leaves; then the entire plant
- Slow growing, rounded leaves that roll upwards
- Stiff and brittle leaves
- Dropping leaves & dead bud tips
- Small, hard and woody roots
GENERAL SYMPTOMS OF SULFUR EXCESS IN PLANTS
May be induced from air pollution so difficult to control. Results in premature dropping of leaves.
MICRONUTRIENT DEFICIENCY AND EXCESS SYMPTOMS IN PLANTS
FUNCTION OF BORON IN PLANTS
Boron helps with the development of cell walls and in the production of fruits and vegetables. Boron is essential but in very small quantities. The line between deficiency and excess is narrow. Boron is extremely mobile in soil. As a result, deficiency often occurs in areas of high rainfall. Deficiencies may also occur if soil pH is 6.0 and 7.5, in deeply sandy soils, or when high Levels of Nitrogen, Potassium and Calcium are present. Deficiency will be more noticeable during drought conditions.
GENERAL SYMPTOMS OF BORON DEFICIENCY IN PLANTS
- Stunted and distorted growth -- new tissue is affected first
- Scorched and curled leaves
- Smallish leaves; may also be thick and brittle
- Reduced flowering; failure to set seed
- Discoloration in vegetable plants -- produce poorly developed
GENERAL SYMPTOMS OF BORON EXCESS IN PLANTS
Scorched leaf edges; eventually, prematurely dropped leaves.
FUNCTION OF COPPER IN PLANTS
Copper functions as a catalyst in plant photosynthesis and respiration. It affects the formation of lignin in cell walls and contributes to the structural strength of the plant. Copper also affects the flavor and sugar content of fruit. Copper deficiency occurs more often in highly organic and/or very sandy soils than in loam that contains a good amount of clay. Because Copper is relatively immobile a constant supply is needed throughout the growing season. Symptoms appear on new growth first.
GENERAL SYMPTOMS OF COPPER DEFICIENCY IN PLANTS
- New growth is small/stunted, or is misshapen/twisted or is wilted
- Inter-vein chlorosis in young leaves while tips of older leaves remain green
- Vegetable leaves become a bluish-green color, become chlorotic, then curl
- Prone to disease
GENERAL SYMPTOMS OF COPPER EXCESS IN PLANTS
Toxic levels of Copper rarely occur naturally. Excess can result, however, when large quantities of sewage sludge are present. Excess may also occur from use of copper-containing fungicides or fertilizers.
FUNCTION OF IRON IN PLANTS
Iron enables other nutrients (elements) to travel through the plant’s circulatory system. Without Iron, a plant cannot produce chlorophyll, cannot get oxygen and will not be green. Iron deficiency produces yellow leaves but that is a not enough for a diagnosis because yellow leaves are a common result when many nutrients are deficient. Symptoms may appear on a single branch or on the entire plant. Iron deficiency is likely to occur in areas with high pH soils such as exist in the western USA (pH 7.0 and above). Iron may be unavailable for plant uptake when the soil is high in lime content (calcium carbonate). Iron chlorosis can also be a symptom of springtime over-watering and soil compaction.
Note to Pin Oak fans. This popular tree is prone to iron deficiencies. It is often seen with yellow leaves and dead patches in the branches. Pin Oak should be planted in a moist, well drained area with plenty of organic matte (and not along the sidewalk or roadside).
GENERAL SYMPTOMS OF IRON DEFICIENCY IN PLANTS
- Yellowing of leaves while veins remain green
- Stunted development of plant’s new growth and its youngest leaves
- Poor fruit production
GENERAL SYMPTOMS OF IRON EXCESS IN PLANTS
Plants don’t require much Iron so an excess can kill a plant. Excess affects a plant’s ability to draw in other essential nutrients, such as Phosphate and Nitrogen, without which a plant cannot function.
FUNCTIONS OF MANGANESE IN PLANTS
Manganese contributes to photosynthesis, accelerates germination and pollination, increases the availability of Phosphorus and Calcium, and supports the movement of Iron. Manganese deficiency symptoms are similar to those of Iron deficiency or toxicity. The deficiency occurs in soils that have high pH (6.5, or more) or have substantial amounts of organic material. Excessive water, poor aeration, and excess heavy metals also influence Manganese uptake.
GENERAL SYMPTOMS OF MANGANESE DEFICIENCY IN PLANTS:
- Yellowing of leaves
- Reduced or stunted plant growth
- Reduced level of germination
- Poor number of blooms and size of blooms
GENERAL SYMPTOMS OF MANGANESE EXCESS IN PLANTS
Results in brown spotting of leaves; mimics symptoms of Iron deficiency. Zonal geraniums, marigolds and impatiens are especially susceptible to excess Manganese excess.
FUNCTION OF MOLYBDENUM IN PLANTS
Molybdenum absorption is very sensitive to soil pH. Absorption increases with increases in pH. Legumes, cabbage and cauliflower require relatively high levels of the nutrient. Molybdenum affects pollen and fruit formation. Molybdenum deficiency resembles Nitrogen deficiency. Molybdenum is highly mobile so symptoms are typically seen on old growth first. Most soils contain enough Molybdenum in available form to adequately meet plant needs. Molybdenum deficiency most often occurs in regions of acid, sandy soils, particularly when pH is greater than 5.5.
GENERAL SYMPTOMS OF MOLYBDENUM DEFICIENCY IN PLANTS
- Reduced growth
- Pale and withered leaves
- Poorly developed product (beans, cabbage, etc.)
- See Nitrogen deficiency for more symptoms
GENERAL SYMPTOMS OF MOLYBDENUM EXCESS IN PLANTS
Most plants are very tolerant of excessive amounts of Molybdenum in the tissue without any harmful effects.
FUNCTION OF ZINC IN PLANTS
Zinc performs many functions. It is necessary for proper root development, influences the rate of stalk and seed maturity and enables the plant to survive lower air temperatures. Zinc deficiency is the most widespread micronutrient deficiency problem. Chalky, sandy soils, peat soils, and soils with high phosphorus and silicon content is likely to be Zinc deficient. Soils low in organic material (typical of new yards where topsoil has been removed) are also susceptible. Stunted growth is a common symptom of Zinc deficiency.
GENERAL SYMPTOMS OF ZINC DEFICIENCY IN PLANTS
- General stunting of plant; discoloration of leaves
- Chlorosis in lower leaves (other nutrient deficiencies tend to begin in upper leaves)
- Plants especially sensitive to insufficient levels of Zinc: snap beans, dry beans, sweet corn, citrus, most orchard crops, and pecans
GENERAL SYMPTOMS OF ZINC EXCESS IN PLANTS
Zinc toxicity in plants is rare. If it occurs, it is likely to restrict uptake of other nutrients. That complicates a diagnosis because what becomes visible are symptoms associated with the other nutrients.
“Plant Nutrition” - Colorado Master Gardener Program
“Nutrient Deficiency Symptoms - Barbara J. Bromley, Mercer County Horticulturist 10
“Action Mode, Deficiency and Toxicity Symptoms of the 17 Essential Nutrients” - Erv Evans, Consumer Horticulturalist, NC State University