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Feeding Your Plants

Here, you’ll find essential information about plant nutrition in terms of fertilizers—aka NPK—as well as the necessary micronutrients for optimal growth and development.

Fertilizing is the practice of providing plants with the nutrients they need to grow, develop, and perform at their best. Fertilizers are products formulated to supply these essential nutrients, either individually or in specific combinations, depending on the needs of the plant and growing environment.

Fertilizers come in different forms and types, including liquid fertilizers, water-soluble products, slow-release formulations, and more, derived from either organic or synthetic sources. They can be applied directly to, or mixed into, the soil or growing medium, delivered through irrigation, or applied to the foliage, depending on the product and its intended use.

Understanding what nutrients a fertilizer provides, how much it provides, and how it should be applied is crucial for making informed and safe decisions about plant nutrition.

Understanding NPK

NPK stands for nitrogen (N), phosphorus (P), and potassium (K)—the three primary nutrients plants require in the greatest amounts, also known as the primary macronutrients. The three numbers you see on a fertilizer label represent its NPK ratio, always listed in that order. These numbers indicate the percentage of each nutrient in the fertilizer by weight, giving you a clear picture of the fertilizer’s primary nutrient composition - For example, a 6-4-8 fertilizer provides 6% Nitrogen(N), 4% Phosphorus(P), and 8% Potassium(K). Together, they play a fundamental role in supporting healthy plant growth, development, and overall performance. The different ratios allow fertilizers to be formulated for different plant needs, growth stages, and growing conditions.

N Nitrogen (N)

What is it?

Nitrogen is an essential macronutrient that plays a key role in plant growth and development. It is involved in the production of chlorophyll, amino acids, proteins, and DNA, making it important for healthy growth and development.

How it works

Plants mainly take up nitrogen in the forms of nitrate and ammonium. Once absorbed, nitrogen becomes part of compounds the plant uses to produce proteins, support growth, and carry out essential processes.

Why plants need it

  • Chlorophyll formation and photosynthesis: Nitrogen is needed to produce chlorophyll, which allows plants to capture light energy for photosynthesis.
  • Amino acid and protein production: Nitrogen is a building block of amino acids, which plants use to make proteins needed for growth and normal plant functions.
  • Enzyme production and activity: Nitrogen is part of many enzymes that help control important chemical reactions inside the plant.
  • DNA and RNA formation: Nitrogen is part of DNA and RNA, which carry genetic information and help regulate growth and development.
  • Leaf and vegetative growth: Adequate nitrogen supports healthy leaf, stem, and shoot growth, especially during active vegetative growth.
  • Overall plant growth and development: Because nitrogen is involved in many essential plant processes, an adequate supply is important for healthy growth and development.

Deficiency symptoms

General chlorosis of older, lower leaves, with uniform yellowing across the entire leaf. Because nitrogen is mobile within the plant, symptoms usually appear on older leaves first. As deficiency worsens, plants may show slow or stunted growth, smaller leaves, thin stems, and premature leaf drop.

P Phosphorus (P)

What is it?

Phosphorus is an essential macronutrient that plays an important role in plant growth and development. It is involved in energy transfer, root development, cell growth, and the formation of DNA and RNA. It also supports reproductive growth, including the development of flowers, fruits, and seeds.

How it works

Plants mainly take up phosphorus in the form of phosphate. Once absorbed, phosphorus becomes part of compounds the plant uses to store and transfer energy, build cells, and support growth and reproduction.

Why plants need it

  • Energy transfer: Phosphorus is part of ATP (adenosine triphosphate), which helps store and transfer energy throughout the plant.
  • Root development: Phosphorus supports healthy root growth and development, especially during early plant growth.
  • DNA and RNA formation: Phosphorus is part of DNA and RNA, which are essential for cell growth and development.
  • Cell formation: Phosphorus is part of cell membranes and supports the formation and function of plant cells.
  • Flower, fruit, and seed development: Phosphorus supports reproductive growth and helps with the development of flowers, fruits, and seeds.
  • Photosynthesis and metabolism: Phosphorus is involved in processes that allow plants to capture, transfer, and use energy.

Deficiency symptoms

Dark green or dull-looking leaves and slow, stunted growth, usually appearing first on older leaves. As the deficiency becomes more severe, plants may develop reddish-purple coloration, poor root growth, delayed maturity, and reduced flower, fruit, or seed development. Older leaves may eventually develop brown or dead areas.

K Potassium (K)

What is it?

Potassium is an essential macronutrient that helps regulate many important processes in plants. It supports water balance, enzyme activity, photosynthesis, root growth, and the plant's ability to handle environmental stress.

How it works

Plants mainly take up potassium in the form of potassium ions. Once absorbed, potassium helps regulate water balance, activate enzymes, and support many processes involved in plant growth and development.

Why plants need it

  • Water regulation: Potassium helps maintain water balance within plant cells and reduces water loss
  • Root growth: Potassium supports healthy root growth and helps plants make better use of available water.
  • Enzyme activity: Potassium activates many enzymes involved in plant growth and metabolism.
  • Photosynthesis: Potassium supports photosynthesis and helps regulate the processes involved in producing and using plant sugars.
  • Sugar and carbohydrate transport: Potassium helps move sugars and other products of photosynthesis from leaves to growing and storage tissues.
  • Stomatal regulation: Potassium helps control the opening and closing of stomata, which regulate gas exchange and water loss.
  • Stress tolerance: Adequate potassium helps plants better tolerate stresses such as drought and water loss.

Deficiency symptoms

Yellowing and browning along the edges and tips of older leaves, often progressing inward toward the center of the leaf. As the deficiency becomes more severe, the leaf edges may become dry or scorched, and plants may show slow or stunted growth and reduced overall health.

Secondary Macros

Ca Calcium (Ca)

What is it?

Calcium is an essential secondary macronutrient that plays an important role in plant structure and growth. It becomes part of cell walls, helps maintain cell membranes, and supports the development of new tissues, roots, and growing points.

How it works

Calcium is absorbed by the roots and transported mainly with water through the plant. Because calcium is relatively immobile within plant tissues, a steady supply is especially important for actively growing areas, where it helps maintain cell structure and support new growth.

Why plants need it

  • Cell wall formation: Calcium becomes part of cell walls, helping give plant tissues strength and structure.
  • Cell membrane function: Calcium helps maintain the structure and stability of cell membranes.
  • New growth: Calcium is important for the development of new leaves, shoots, and growing points.
  • Root development: Calcium supports healthy root growth and the development of root tips.
  • Cell growth and division: Calcium is involved in processes that support cell division and the formation of new plant tissue.
  • Plant signaling: Calcium helps transmit signals inside plant cells, allowing plants to respond to changes in their environment.

Deficiency symptoms

Distorted, curled, or damaged new growth, often with browning or dead areas on young leaves and growing points. Because calcium is relatively immobile within the plant, deficiency symptoms usually appear first in actively growing tissues. Severe deficiency can damage or kill growing points and root tips. In crops such as tomatoes and peppers, inadequate calcium reaching developing fruit can contribute to blossom-end rot. However, blossom-end rot does not necessarily mean that the soil lacks calcium; fluctuations in soil moisture, root damage, rapid growth, and other factors can interfere with calcium uptake and movement to the fruit.

Mg Magnesium (Mg)

What is it?

Magnesium is an essential secondary macronutrient that plays an important role in photosynthesis and plant growth. It is a central part of the chlorophyll molecule and helps activate enzymes involved in many processes within the plant.

How it works

Magnesium is absorbed by the roots and transported throughout the plant. It becomes part of chlorophyll and supports enzyme activity involved in photosynthesis, metabolism, and the production and use of energy.

Why plants need it

  • Chlorophyll formation: Magnesium is a central part of chlorophyll, allowing plants to capture light energy for photosynthesis.
  • Photosynthesis: Magnesium supports the processes plants use to convert light energy into chemical energy.
  • Enzyme activation: Magnesium activates many enzymes involved in plant metabolism and growth.
  • Energy production: Magnesium supports processes involved in producing and using energy within plant cells.
  • Protein formation: Magnesium supports enzyme systems involved in the production of proteins and other plant compounds.
  • Plant growth: Magnesium contributes to healthy growth and development by supporting photosynthesis and other essential plant processes.

Deficiency symptoms

Interveinal chlorosis, where the areas between the leaf veins turn yellow while the veins remain green. Because magnesium is mobile within the plant, deficiency symptoms usually appear first on older leaves as magnesium is moved to younger, actively growing tissues. Severe deficiency can cause leaves to develop brown or dead areas, curl, and eventually drop.

S Sulfur (S)

What is it?

Sulfur is an essential secondary macronutrient that plays an important role in protein formation and plant growth. It is a component of certain amino acids and is used to produce proteins, enzymes, and other compounds needed for healthy plant development.

How it works

Sulfur is absorbed mainly through the roots and becomes part of important compounds within the plant, where it supports protein formation, enzyme activity, and other processes involved in growth and development.

Why plants need it

  • Protein formation: Sulfur is part of amino acids that plants use to build proteins needed for growth and development.
  • Enzyme function: Sulfur is part of compounds involved in the formation and function of certain enzymes.
  • Plant metabolism: Sulfur supports metabolic processes that help plants grow and develop.
  • Photosynthesis: Sulfur supports the formation of proteins and enzymes involved in photosynthesis.
  • Plant growth: Sulfur contributes to healthy growth by supporting protein production and other essential processes.
  • Plant compounds: Sulfur is used to produce compounds that play important roles in plant function and responses to environmental conditions.

Deficiency symptoms

Uniform yellowing or pale green coloration of younger leaves, often accompanied by reduced or slow growth. Because sulfur is relatively immobile within the plant compared with nutrients such as nitrogen, deficiency symptoms commonly appear first in young leaves and growing tissues. Severe deficiency can result in smaller, thinner leaves, overall pale coloration, and reduced plant growth.

Essential Micronutrients

Micronutrients are essential elements that plants need in much smaller amounts than NPK, but still play an important role for healthy growth, development, and overall plant function. While NPK provides the primary nutrients plants need in larger quantities, micronutrients support many of the processes that allow plants to properly use those nutrients and function efficiently. They are included in fertilizers to help maintain a more complete nutrient profile and to prevent deficiencies that can affect plant health and performance.

Fe Iron (Fe)

What is it?

Iron is an essential micronutrient best known for its role in photosynthesis and chlorophyll production. Although plants need only very small amounts, iron is critical for proteins and enzymes involved in the processes that keep photosynthesis and plant metabolism functioning.

How it works

Iron supports processes involved in photosynthesis and energy transfer within the plant. It is also required for the biochemical processes involved in making chlorophyll, which is why a plant can contain iron in its tissues yet still develop iron deficiency when that iron is not available for use.

Why plants need it

• Chlorophyll production: Iron is required for the processes that produce chlorophyll and maintain healthy green foliage.
• Photosynthesis: Iron supports processes that allow photosynthesis to function properly.
• Energy production: Iron-containing proteins help transfer energy within plant cells.
• Nitrogen use: Iron is involved in enzymes that help plants process nitrogen.
• Plant metabolism: Iron supports several enzyme systems essential for normal plant function.

Deficiency symptoms

Young leaves develop strong interveinal chlorosis, with the tissue between the veins turning yellow while the veins remain green. In severe cases, new leaves can become very pale or almost white. Because iron is relatively immobile within the plant, symptoms generally show up first on young, actively growing tissue.

Mn Manganese (Mn)

What is it?

Manganese is an essential micronutrient with a particularly important role in photosynthesis and enzyme activation. It is also involved in nitrogen metabolism, lignin formation, and root development.

How it works

One of manganese's most distinctive jobs occurs inside the photosynthetic machinery, where it is essential to the process that splits water during photosynthesis. Manganese also activates enzymes that control a wide range of plant reactions.

Why plants need it

• Photosynthesis: Manganese is essential to the water-splitting reaction that supplies what the plant needs to keep photosynthesis going.
• Enzyme activation: It activates numerous enzymes involved in plant metabolism.
• Nitrogen metabolism: Manganese contributes to how plants process and use nitrogen.
• Lignin formation: It supports the production of lignin, which contributes to plant structural strength.
• Root development: Adequate manganese supports healthy root growth.
• Plant defense: Manganese contributes to systems that help protect plant cells from oxidative damage.

Deficiency symptoms

Interveinal chlorosis develops on younger leaves, often producing a fine, checkered or fishbone-like pattern because the smaller veins remain green. As the deficiency progresses, small brown or gray necrotic spots may appear within the yellow areas, followed by reduced growth in more severe cases.

Zn Zinc (Zn)

What is it?

Zinc is an essential micronutrient that helps regulate plant growth, protein production, and enzyme activity. It is particularly important in the processes that control how plants develop new tissue and use genetic information.

How it works

Rather than being associated with one major visible process like chlorophyll production, zinc works largely through zinc-containing proteins and enzymes that regulate cellular activity. It also contributes to the production of auxin, a plant hormone involved in shoot and cell growth.

Why plants need it

• Growth regulation: Zinc supports normal development of shoots and leaves.
• Protein production: Zinc is needed for processes involved in making proteins.
• Plant hormones: Zinc contributes to the production of auxin, which regulates growth.
• Enzyme activity: Zinc is part of enzymes responsible for important metabolic reactions.
• Leaf development: Adequate zinc is important for normal leaf size and shape.
• Reproductive growth: Zinc contributes to normal flowering, fruit development, and seed production.

Deficiency symptoms

Young leaves become small, pale, and sometimes distorted, while the spaces between leaves become unusually short. This can produce a compact or rosetted appearance. Interveinal chlorosis may also develop, and severe deficiency can cause pronounced stunting and reduced reproductive growth

Cu Copper (Cu)

What is it?

Copper is an essential micronutrient involved in photosynthesis, enzyme activity, and the development of strong plant tissues. It is needed in very small amounts, but too little can seriously affect new growth and reproduction.

How it works

Copper is part of proteins involved in photosynthesis and is also associated with several enzymes involved in important chemical reactions. It therefore helps the plant carry out processes necessary for growth and development.

Why plants need it

• Photosynthesis: Copper-containing proteins participate in important processes during photosynthesis.
• Enzyme function: Copper is required by several important enzymes.
• Structural development: Copper contributes to the formation and strengthening of plant tissues.
• Reproductive growth: Adequate copper supports flowering, pollen development, and seed formation.
• Shoot development: Copper is particularly important for healthy new growth and growing points.

Deficiency symptoms

Deficiency tends to show up first in young growth because copper is relatively immobile within the plant. New leaves may be small, twisted, bluish-green, or wilted, while leaf tips and margins can develop yellowing and necrosis. Severe deficiency can cause the growing point to stop developing and can reduce normal reproductive development.

B Boron (B)

What is it?

Boron is an essential micronutrient that is especially important for actively growing tissues, cell wall development, and reproduction. Its effects are most noticeable where plants are producing new cells, roots, flowers, pollen, and developing fruit.

How it works

Boron helps maintain the structure of growing cells and plays an important role in cell wall formation and membrane function. It is also critical during flowering because it supports pollen germination and pollen tube growth.

Why plants need it

• Cell wall development: Boron helps maintain the structure and integrity of growing plant cells.
• Growing points: It is particularly important for meristems, root tips, and other actively dividing tissues.
• Root growth: Boron supports healthy root elongation and development.
• Flowering: Boron is important for pollen germination and pollen tube growth.
• Fruit and seed development: Adequate boron supports normal reproductive development.
• Plant metabolism: Boron supports several processes involved in healthy growth and development.

Deficiency symptoms

Deficiency typically affects growing points first. Young leaves may become distorted, brittle, thickened, or develop dead areas, while shoot tips and root tips can stop growing or die. Poor flowering, pollen development, fruit set, or seed development can also occur. Because boron has limited mobility in most plants, symptoms are generally concentrated in new growth and reproductive tissues. Grower note: boron has a particularly narrow range between deficiency and toxicity, so more is definitely not better.

Mo Molybdenum (Mo)

What is it?

Molybdenum is an essential micronutrient with a very specific connection to nitrogen use. Plants need it in tiny amounts, but without enough molybdenum they cannot properly process nitrate nitrogen.

How it works

Molybdenum is part of enzymes involved in nitrogen metabolism, most importantly nitrate reductase, which allows plants to convert nitrate into forms they can use to build amino acids and proteins. In legumes, molybdenum is also important to the nitrogen-fixing process carried out by root-nodule bacteria.

Why plants need it

• Nitrate utilization: Molybdenum allows plants to process nitrate nitrogen.
• Protein formation: By supporting nitrogen metabolism, it indirectly enables the production of amino acids and proteins.
• Nitrogen fixation: Molybdenum is important for biological nitrogen fixation in legumes.
• Nodule function: Adequate molybdenum supports effective nitrogen-fixing nodules.
• Reproduction: Molybdenum also contributes to pollen viability and seed production.

Deficiency symptoms

Molybdenum deficiency can look surprisingly similar to nitrogen deficiency: plants become pale, stunted, and lack vigor, often with symptoms beginning on older or middle-aged leaves. Marginal yellowing or scorching can develop, and some crops develop characteristic leaf distortion. In cauliflower and related crops, severe deficiency can produce “whiptail,” where leaves become narrow and distorted. In legumes, poor nodulation and reduced nitrogen fixation can make the plant appear nitrogen deficient even when nitrogen is present in the soil.

Cl Chlorine (Cl)

What is it?

Chlorine is an essential micronutrient that is often overlooked because plants require it in very small amounts and deficiency is uncommon. Its main roles are connected to water balance, cell pressure, and photosynthesis.

How it works

Chlorine helps regulate water balance within plant cells. It contributes to maintaining cell turgor, supports photosynthetic reactions, and helps maintain the chemical balance needed for normal cell function.

Why plants need it

• Water balance: Chlorine helps plants maintain proper water status within their cells.
• Cell turgor: It contributes to the internal pressure that keeps plant tissues firm.
• Photosynthesis: Chlorine participates in photosynthetic reactions.
• Cell function: It helps maintain the chemical balance needed for normal cellular activity.
• Root development: Adequate chlorine supports normal root growth and development.

Deficiency symptoms

Chlorine deficiency is rare in most growing systems, but when it occurs, plants may wilt despite adequate water, followed by chlorosis, bronzing, and eventually necrosis of the leaves. Leaf growth and root development may also be reduced.

Ni Nickel (Ni)

What is it?

Nickel is an essential micronutrient required in extremely small amounts. Its clearest and best-established role is in nitrogen metabolism, particularly through its function in the enzyme urease.

How it works

Nickel is required for urease to break down urea into forms the plant can use. This matters both when urea is supplied as a nitrogen source and because plants naturally produce urea during normal nitrogen metabolism. Nickel also has important connections with nitrogen fixation in legumes.

Why plants need it

• Urea metabolism: Nickel enables urease to break down urea so nitrogen can be properly recycled and used.
• Nitrogen metabolism: It supports normal processing of nitrogen within plant tissues.
• Nitrogen fixation: Nickel contributes to efficient nitrogen fixation in legumes.
• Seed development: Adequate nickel is important for normal seed development and viability.
• Plant growth: Severe nickel deficiency can disrupt normal growth because nitrogen metabolism becomes impaired.

Deficiency symptoms

Nickel deficiency is uncommon, but when it occurs, plants can accumulate excess urea in their tissues. This can lead to brown or dead leaf tips, chlorosis, and premature leaf drop. One of the most recognizable examples is “mouse-ear” in pecans, where new leaflets are unusually small with rounded or blunt tips. In legumes, poor nodulation and reduced nitrogen fixation may also occur.

Co Cobalt (Co)

What is it?

Cobalt is a trace element with an important role in biological nitrogen fixation, but its status is different from the other micronutrients in this list. Cobalt is not universally recognized as an essential nutrient for all higher plants. Its strongest established importance is to the microorganisms that fix atmospheric nitrogen, particularly bacteria associated with the root nodules of legumes.

How it works

In nitrogen-fixing systems, cobalt is needed by microorganisms involved in producing and using vitamin B12-dependent enzymes. These microorganisms use those systems to support nitrogen fixation, allowing legumes to obtain usable nitrogen from atmospheric nitrogen.

Why plants need it

• Nitrogen fixation: Cobalt supports the microorganisms responsible for biological nitrogen fixation.
• Root nodules: It helps maintain the activity of nitrogen-fixing bacteria associated with legumes.
• Nitrogen supply: By supporting these microorganisms, cobalt can indirectly improve the plant's access to biologically fixed nitrogen.
• Microbial activity: Cobalt is particularly relevant where plant growth depends on beneficial nitrogen-fixing microbial relationships.

Deficiency symptoms

This is not as straightforward as diagnosing an iron or zinc deficiency. There is limited evidence for a distinct, universal cobalt-deficiency symptom in higher plants. Where cobalt is limiting nitrogen-fixing systems, the more meaningful effect can be poor nodulation, reduced nitrogen fixation, and symptoms resembling nitrogen deficiency, particularly in legumes. Cobalt itself can also become toxic at excessive concentrations, so it should not be treated as a nutrient where “more is better.”

Grower note: Cobalt should be thought of primarily in the context of plant–microbe relationships and nitrogen fixation, rather than as a conventional essential micronutrient required by every crop.