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Plants’ nutrient requirements

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Rhododendron.
Photo: Jardin botanique de Montréal (Michel Tremblay)

Plants need 16 essential nutrients, or elements. These include the carbon (C), oxygen (O) and hydrogen (H) they draw from water and the air. The remaining elements are drawn from the soil. These nutrients can be divided into three categories: primary (macronutrients), secondary and minor (micronutrients).

Primary elements (macronutrients)

Plants need large quantities of these elements. That is why they are called “primary” or “macronutrients.”

Element Role in plant growth
Nitrogen (N) Basic component of proteins and chlorophyll (the pigment that gives plants their green colour). Plays an essential role in plant growth. Also feeds microorganisms in the soil.
Phosphorous (P) Plays an important role in root growth and promotes the establishment of young plants, flowering, fruiting and ripening, photosynthesis, respiration and overall plant growth.
Potassium (K) Moves through the plant. Promotes the movement of sugars, turgor and stem rigidity. Also increases the plant’s overall resistance to cold, diseases, insect pests, etc. Promotes the formation of flower buds, the hardening-off of woody plants and fruiting.

Secondary elements

Less of these elements is required than of primary elements.

Element Role in plant growth
Calcium (Ca) Plays a vital role in plant structure, because it is part of cell walls and holds them together. Promotes the development of the root system and the ripening of fruit and seeds. Found in the growing parts of plants (apex and buds).
Magnesium (Mg) An important part of chlorophyll. Helps fruit ripen and seeds germinate. Reinforces cell walls and promotes the absorption of phosphorous, nitrogen and sulphur by plants.
Sulphur (S) A component of several proteins, enzymes and vitamins. Contributes to chlorophyll production. Helps plants absorb potassium, calcium and magnesium.

Minor elements (micronutrients)

Although only small quantities of these elements are required, they are essential to plant growth.

Element Role in plant growth
Iron (Fe) Essential to chlorophyll production. Also contributes to the formation of some enzymes and amino acids.
Boron (B) Essential to overall plant health and tissue growth. Promotes the formation of fruit and the absorption of water.
Manganese (Mn) Promotes seed germination and speeds plant maturity. Plays an important role in photosynthesis by contributing to chlorophyll production. Essential for nitrogen assimilation and protein formation.
Molybdenum (Mo) Essential for nitrogen assimilation by plants and nitrogen fixation by bacteria. This means that it is needed for the production of nitrogen-based proteins.
Chlorine (Cl) Stimulates photosynthesis.
Copper (Cu) Activates various enzymes. Also plays a role in chlorophyll production.
Zinc (Zn) Plays an important role in the synthesis of proteins, enzymes and growth hormones.

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