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Organic Plant Nutrients for Vegetable Gardens

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Plants require nutrients to grow and for good health. Most plant nutrients are common natural organic chemical elements. Sixteen organic chemical elements are the nutrients necessary for plant growth. Three are non-mineral elements that come from air and water; thirteen are mineral elements that come from the soil. All of these elemental nutrients in varying amounts are needed for plant life.

Elemental organic plant nutrients are generally used in one of three ways:

  • They become part of plant cells and are basic to the structure of plants.
  • They are metabolic, required for biochemical functions within the plant such as photosynthesis or reproduction.
  • They are catalysts that assist metabolic functions.

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Being familiar with the elements necessary for plant growth will help you diagnose many plant problems and aid you in the selection of plant foods and fertilizers and soil amendments

Most of the elements that plants need to grow come from the soil. Keeping the soil healthy is the quickest and least expensive way to ensure healthy and productive crops.

Here is a primer on elements necessary for plant growth, the basic plant nutrients.

Non-mineral nutrients: elements from air and water

  • Carbon (C)
  • Hydrogen (H)
  • Oxygen (O)

Plant photosynthesis converts carbon dioxide (CO2–carbon and water) and water (H2O –hydrogen and oxygen) into starches and sugars that plants use as food.

Mineral nutrients

Elements from air and soil:

  • Nitrogen (N)
  • Elements from soil and fertilizers:
  • Phosphorus (P)
  • Potassium (K)
  • Calcium (Ca)
  • Magnesium (Mg)
  • Sulfur (S)
  • Boron (B)
  • Chlorine (Cl)
  • Copper (Cu)
  • Iron (Fe)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Zinc (Zn)

Mineral nutrients from the soil are dissolved in water and absorbed through plant roots. These elements are responsible for plant growth, plant functioning, leaf, flower, and fruit production, and plant health. When soil does not contain all of these elements or nutrients, gardeners add natural soil amendments or fertilizers to make up for the deficiency.

Mineral macronutrients and micronutrients

Mineral nutrients are divided into major or macronutrients and minor or micronutrients. Macronutrients are further divided into primary macronutrients and secondary macronutrients.


The primary macronutrients are:

  • Nitrogen (N)
  • Phosphorus (P)
  • Potassium (K)

These nutrients are usually in the soil in some amount unless plants have already used them. When the soil lacks these nutrients, they can be added with natural soil amendments–such as aged compost or aged manure–or specific natural or synthetic fertilizers.

The secondary macronutrients are:

  • Calcium (Ca)
  • Magnesium (Mg)
  • Sulfur (S)

These nutrients are usually in the soil. When they are lacking, they can be added with natural soil amendments–such as aged compost–or specific natural or synthetic fertilizers.


Micronutrients are also known as minor nutrients or trace elements. Plant micronutrients include:

  • Boron (B)
  • Chorine (Cl)
  • Copper (Cu)
  • Iron (Fe)
  • Manganese (Mn)
  • Molybdenum (Mo)
  • Zinc (Zn)

Micronutrients are needed only in very small amounts. When micronutrients are lacking, they can be added with natural soil amendments–such as grass clippings or leaves–or natural or synthetic fertilizers.

Nutrients in the soil and air

Plants require the macronutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S) from the soil. Plants also need micronutrients from the soil: iron (Fe), boron (B), copper (Cu), zinc (Zn), and manganese (Mn). From the air, plants require carbon (C), hydrogen (H), and oxygen (O).


Of the macronutrients, nitrogen is essential for shoot and leaf growth especially in the early part of the growing season. Phosphorus is important in the formation of roots. Potassium aids flower and fruit formation and general plant health.

Plant nutrients to grow vegetables
Mineral elements for plant growth

Feeding the soil

The regular addition of organic material to the garden—aged compost and manure—provides almost all the minerals required to support vegetable, herb, and fruit growth. A soil’s structure, moisture-holding capacity, and drainage are improved with the addition of compost and manure and so is its store of essential plant nutrients.


Additional soil additives and fertilizers are seldom required once the soil is fertile and receives light composting and manuring regularly. Additives and fertilizers added to a balanced soil are akin to seasonings added as a finishing touch to a meal. They are best used on a plant by plant basis to supplement the work of healthy soil. 

Organic soil amendments

Few gardeners have perfect soil. Almost all soils can be improved with the addition of organic amendments. An organic soil amendment is any natural material that improves soil structure. Organic amendments not only improve soil structure but also increase soil fertility by releasing nutrients as the organic matter decomposes.

The best soil amendments are finished compost, rotted manure, chopped leaves, straw, and grass clippings. Adding one inch of nearly fully decomposed organic matter to the garden once or twice a year will improve and refresh the soil almost immediately.

How amendments help the soil

Organic soil amendments increase the moisture and nutrient-holding capacity of sandy soils and allow water and air to flow easily through clay soils. Adding partially decayed organic compost will increase soil fertility by releasing nutrients, particularly nitrogen, as the organic matter decomposes.

Organic matter helps stimulate the growth and reproductive capacity of soil microorganisms and worms that in turn add humus to the soil. (Keep in mind that worms and soil microorganisms work more quickly to decompose organic matter in warm weather than in cool weather.)

Soil nutrients for vegetables
Mineral elements in the soil help plants grow.

How chemical elements help plants

Here are key elements from the soil and how they help plants:

  • Nitrogen (N): essential to plant growth; part of the chlorophyll molecule, which gives plants their green color and is involved in creating food for the plant through photosynthesis.
  • Phosphorus (P): essential for plant cell division and development of new tissue; aids in complex energy transformations in the plant that help convert other nutrients into usable building blocks for growth.
  • Potassium (K): an essential element for plant growth; helps plants use water and resist drought and enhances fruits and vegetables. 
  • Sulfur (S): essential for the growth and development of plants; a key to the formation of chlorophyll that permits photosynthesis through which plants produce starch, sugars, oils, fats, vitamins, and other compounds.
  • Magnesium (Mg): essential for photosynthesis in plants; without magnesium, chlorophyll cannot capture sun energy needed for photosynthesis. 
  • Calcium (Ca): crucial for plant growth and makes plants less susceptible to diseases and pests.
  • Iron (Fe):  enzyme and chlorophyll production, nitrogen-fixing, and development and metabolism are all dependent on iron.
  • Boron (B): increases flower production and retention, pollen tube elongation and germination, and seed and fruit development
  • Copper (Cu): required in the process of photosynthesis, is essential in plant respiration, and assists in plant metabolism of carbohydrates and proteins.
  • Zinc (Zn): helps the plant produce chlorophyll; when the soil is deficient in zinc and plant growth is stunted. 
  • Manganese (Mn): contributes to biological systems including photosynthesis, respiration, and nitrogen assimilation, and also is involved in pollen germination, pollen tube growth, root cell elongation, and resistance to root pathogens.

Here are key elements from the air or atmosphere and how they help plants:

  • Carbon (C): plants take carbon dioxide from the atmosphere and turn it into sugars through photosynthesis; the carbon that plants absorb from the atmosphere in photosynthesis becomes part of the soil when they die and decompose.
  • Hydrogen (H): combines with carbon during the photosynthesis process and releases oxygen into the atmosphere which is used by all living beings; all living beings need oxygen for respiration. 
  • Oxygen (O): essential because it makes the process of plant cell respiration more efficient (known as aerobic respiration).

Plant nutrients, organic sources, signs of deficiency

When vegetables and other plants lack essential nutrients or elements they will not look themselves; they will look unhealthy and they may even die. The symptom of a nutrient deficiency can range from yellowing and poor growth to flower and fruit failure.

Nutrient deficiency symptoms in plants can be confusing. Many plant nutrient deficiencies share the same or very similar symptoms. What is more, symptoms of nutrient deficiency can be similar to symptoms of many plant diseases.

A certain way to know if a plant or crop is suffering from a nutrient deficiency is to have a soil test. Ask the tester to recommend the nutrients and amount necessary to rectify the deficiency.

Here are important mineral plant nutrients, their function, symptoms of deficiency, and fertilizers to help correct deficiencies:

Nitrogen (N)

  • Function: Necessary for rapid green, leafy growth; part of chlorophyll necessary for photosynthesis; part of a protein.
  • Organic source: Manure, bonemeal, blood meal (dried blood), fish meal, fish emulsion (also contain phosphorus and potassium, in small amounts), cottonseed meal (also contains a small amount of phosphorus and an even smaller amount of potassium), coffee grounds (also contains very small amounts of phosphorus and potassium), soybean meal (also contains a small amount of potassium and an even smaller amount of phosphorus), composted legumes (peas, beans, peanuts), ammonium sulfate or nitrate.
  • Signs of deficiency: Lower leaves pale green or bluish then turn yellow (chlorosis); leaves drop, the oldest leaves fall first; leaves are small; stems are thin; plant lacks vigor; growth is spindly or stunted.
  • Signs of excess: Leaves dark green; the plant has excessive leaf growth at the expense of buds and fruits.

Phosphorus (P)

  • Function: Essential to photosynthesis; enables strong growth; encourages blooming and root development, cell wall structure development; moisture conservation; necessary for photosynthesis.
  • Organic sources: Bonemeal, colloidal phosphate, rock phosphate (contains slightly more phosphorus than colloidal phosphate, breaks down more slowly), New Jersey greensand, superphosphate.
  • Signs of deficiency: Lower leaves and stem look reddish or purplish; young leaves look pale; shoots are thin; plants don’t flower or form fruits; premature fruit drop; roots are stunted; cell division is slowed.
  • Signs of excess: Essential elements may be tied up.

Potassium (K)

  • Function: Promotes disease resistance; necessary for root development and cell wall structure development; moisture conservation; promotion of photosynthesis.
  • Organic sources: Potash rock, manure, granite dust or meal (also contains trace elements), greensand (also contains trace elements), New Jersey greensand, fish meal, seaweed, kelp meal (also contains small amounts of nitrogen, smaller amounts of phosphorus and trace elements) wood ashes (also contains some phosphorous, raises soil pH), potassium sulfate or nitrate.
  • Signs of deficiency: Lower leaves spotted, mottled, or curled; leaf tips and edges turn yellow and bronze, then brown and appear dry and scorched; stems are weak; root system is small; plant vigor reduced; plant susceptible to wilting and wilt diseases; fruit is small; fruit is thin-skinned; fruit color is poor; the flavor is poor.
  • Signs of excess: Fruit coarse and poorly colored fruit; reduced absorption of magnesium and calcium.

Calcium (Ca)

  • Function: Cell division, building plant proteins, flowering, fruiting.
  • Organic sources: Calcitic limestone, dolomitic limestone, gypsum, eggshells, oyster shells, fish meal, wood ashes, and slag.
  • Signs of deficiency: The growing tip of a plant is damaged or dies back; tips of new leaves are yellow and appear scorched; young leaves and buds die back; stems are weak; blossom-end of fruit rots; cavities in tomatoes; black heart; black roots.
  • Sign of excess: Intake of potassium and magnesium is reduced.

Magnesium (Mg)

  • Function: Plant strength.
  • Organic sources: Dolomitic limestone, manure, New Jersey greensand, talc, magnesium sulfate (Epsom salts), and green plants.
  • Signs of deficiency: Lower leaves and older leaves mottled–yellow and white patches between green veins of leaves; brownish or purplish patches may form on leaves; old leaves white or yellow; leaves fall prematurely; growth is stunted; poor flower and fruit quality.
  • Signs of excess: Absorption of calcium and potassium is reduced.

Sulfur (S)

  • Function: Healthy growth.
  • Organic sources: Gypsum, composted legumes, composted cabbage leaves; sulfur, superphosphate.
  • Signs of deficiency: Deficiency is rare; young leaves are pale green to yellow; growth is stunted.
  • Signs of excess: Sulfur burn from too low pH.

Boron (B)

  • Function: Important to plant growth.
  • Organic sources: Clover, composted melon plants, borax (add only if prescribed), granite dust.
  • Signs of deficiency: Young leaves are pale green at the base, develop yellow spots, then become twisted, thickened, and curl under; leaves are small; multiple buds; dieback from terminal buds; heart rot (corkiness); internal cork of apples, cracked stem in celery, heart rot and girdle of beets.
  • Signs of excess: Leaves turn yellowish red.

Copper (Cu)

  • Function: Plant growth, utilization of iron.
  • Organic sources: Manure, rock powders, copper sulfate (use with care), neutral copper, composted dandelions, grass clippings, and sawdust.
  • Signs of deficiency: Young leaves turn pale and may become mottled and wilt; leaves develop brown spots; leaf tips dieback; leaves may not grow; growth slows or stops; multiple buds; gum pockets; lack of leaf development in citrus.
  • Signs of excess: Iron uptake blocked

Iron (Fe)

  • Function: Plant growth, chlorophyll, and carbohydrate production.
  • Organic sources: Humus, manure, compost, blood meal, New Jersey greensand; chelated iron, iron sulfate (copperas).
  • Signs of deficiency: Young leaves turn yellow or very pale but veins remain green (chlorosis); growth is weakened and stunted.
  • Signs of excess: None known.

Manganese (Mn)

  • Function: Growth and plant maturation.
  • Organic sources: Oak leaves, leaf mold, carrot tops, alfalfa; manganese sulfate (tecmangam).
  • Signs of deficiency: Leaves mottled yellow and white; brown spots may develop on leaves; plant growth stunted or plant slow to mature.
  • Sign of excess: Tissue dieback in the leaves; dieback surrounded by a yellow border.

Molybdenum (Mo)

  • Function: Essential to many plant functions, converting nitrates into amino acids, and conversion of phosphorus into plant forms.
  • Organic sources: Sodium molybdate.
  • Signs of deficiency: Leaves turn yellow and pale between veins; leaves may become bluish-green; leaves do not open completely; plant growth is stunted.
  • Signs of excess: Poisonous to livestock.

Zinc (Zn)

  • Function: Fruit development.
  • Organic sources: manure, composted corn, ragweed, vetch; zinc sulfate.
  • Signs of deficiency: Young leaves mottled yellow, plant tips stop growing; plants wilt easily. Occurs in peat and alkaline soils: abnormally long, narrow, mottled, yellowed leaves, poor fruiting, dieback. Small, thin, and yellow leaves; yield low; Deficiency leads to iron deficiency, which it resembles. Also, leaves are thickened and malformed, small and narrow. Growth is stunted.
  • Signs of excess: None known.

Related articles:

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Epsom Salt, Milk, and Organic Fertilizers for Tomatoes and Peppers

Vegetable Garden Organic Pest Control

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Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. has more than 10 million visitors each year.

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