Plant nutrition

Like us, plants need a variety of nutrients to stay healthy and thriving. Most of us are aware of the N-P-K needs of plants (these values are clearly listed on the labels of most commercial fertilisers), but there are also several trace minerals and nutrients that are just as important to healthy plant growth. Figuring out what your plants need, how much, and when your plants are deficient can be tricky. A soil test, an eye for symptoms of deficiency, and the appropriate soil additives can help you remedy these problems before they kill your garden.

Below we have created two charts listing the major nutrients necessary to the health of a plant. These nutrients are broken into two categories: macronutrients and micronutrients. Macronutrients, like the N, P, and K, are the nutrients plants use the most. Of these macronutrients, there are those used more, primary, and those used less, secondary. Micronutrients are the nutrients used in very small trace amounts, but play integral roles in plant processes. The tables below explain how each nutrient is used, how to spot a deficiency, and what you can add to your soil to increase the availability of that nutrient to your plant. Some nutrients are readily available in substances that you might find around the home, and others will need to be introduced to your soil via a commercial fertiliser or compost.

Note: Before you begin making amendments to soil—especially if planting in the ground—it is imperative that you obtain a soil test kit confirm deficiencies. In many cases, adding too much of a nutrient can be as detrimental to the plant as a deficiency, preventing it from absorbing all of the nutrients it needs to survive or becoming toxic. Over fertilisation also contributes to runoff pollution in waterways, and can disrupt the microbial balance in your soil. Use a soil test to determine what your soil is lacking with certainty, and use only the fertilisers and supplements that you need to maintain soil nutrition. Some of the supplements suggested in this chart will have an effect on the pH of your soil.

Plant Macronutrients

Primary Nutrients Function in Plant Signs of Deficiency Sources for Fertiliser
Nitrogen (N) Chlorophyll production; promotes rapid growth and maturation; major component of plant proteins and genetic material Pale to yellow leaves; slow or stunted growth; brown or dry leaf tips; low yield
  • Coffee grounds
  • Blood meal
  • Alfalfa meal
  • Seaweed
  • Pee (yes, really)
Phosphorus (P) Helps to stimulate new growth and cell division; assists in protein synthesis; promotes early growth; required for transfer of energy during photosynthesis Slow or stunted growth; unusually dark green leaves and foliage; reddening of leaves and foliage
  • Bone meal
  • Rock phosphate
Potassium (K) Controls opening and closing of stomata; allows efficient use of water; stabilises plant pH; prevents heat stress and drought damage Chlorosis (yellowing between veins in leaves); brown or dry leaf tips; yellow, brown, or purple spots in leaves; sickly overall appearance
  • Greensand
  • Manure
  • Wood ash
  • Seaweed
Secondary Nutrients Function in Plant Signs of Deficiency Sources for Fertiliser
Calcium (Ca) Building structure of plant cells, including walls and membranes New growth or growing tips stunted, malformed or dead; blossom end rot in tomatoes
  • Lime
  • Gypsum
  • Eggshells
Magnesium (Mg) Component of chlorophyll; aids in enzyme functions; assists in metabolism and processing nutrients; involved in synthesis of fats, sugars, and oils Chlorosis (yellowing between veins in leaves); leaf drop
  • Epsom salt
  • Coffee grounds
  • Matches
Sulfur (S) Synthesis of proteins; involved in photosynthesis and enzyme activities Stunted or reduced growth; paling or yellowing of leaves, particularly new leaves; purpling of leaves or leaf edges
  • Gypsum
  • Epsom salt

Plant Micronutrients

Nutrient Function in Plant Signs of Deficiency Sources for Fertiliser
Boron (B) Involved in reproduction, pollination, and seed production; component of cell structure and division Malformed or withered yellow new growth; poor yield; unusually dark and leathery leaves
  • Borax
  • Boric acid
Copper (Cu) Neutralises radicals; necessary for respiration and photosynthesis; aids in the metabolism of nutrients Decaying or aborting blooms; poor growth overall; bluish tips on leaves; black spots on leaves; poor seed production or sterility
  • Copper fertiliser
Zinc (Zn) Forming chlorophyll; component of protein and involved in protein synthesis Chlorosis (yellowing between veins in leaves); poor growth of roots and stems; purpling or blackening of leaves; leaf puckering
  • Rock phosphate
  • Manure
  • Zinc fertiliser
Manganese (Mn) Aids in the movement and accessibility of P, Fe, and Ca; a component of enzymes involved in photosynthesis; regulates hormones required for growth and maturation Yellow spotting in leaves; greying at base of leaves; brown spotting may occur in leaves
  • Dolomitic limestone
  • Manganese fertiliser
Iron (Fe) Required for respiration, metabolism, and photosynthesis; aids in chlorophyll synthesis and energy transfer Chlorosis (yellowing between veins in leaves); leaves are yellow, pale, and nearly white in extreme cases; paling of leaves affects new growth; new growth appears stunted
  • Iron fertiliser
  • Blood meal
  • Bone meal
Chlorine (Cl) Works with K to control stomata and regulate water usage in the plant; helps to move other nutrients through the plant Yellow spotting or mottling on the leaves of the plant; wilting
  • Chloride fertiliser
Molybdenum (Mo) Required for nitrogen fixation and nitrate reduction in legumes; required for the absorption and conversion of nitrogen in the plant Stunted leaves; chlorosis (yellowing between veins in leaves); burned leaf margins or edges; whiptail in cauliflower
  • Molybdenum fertiliser

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