There are 13 mineral nutrients known to be important to a plant’s health. The 3 you will be most familiar with are: Nitrogen (N), Phosphorus (P) and Potassium (K)
They are collectively classified primary macronutrients. (Macronutrients being nutrients that are consumed in larger quantities while micronutrients are those consumed in smaller quantities). These 3 plant nutrients are essential for plant growth, health and for the process of photosynthesis. Plants use larger amounts of these 3 nutrients than any other nutrient and as such the soil can easily become depleted of them, requiring fertilizers (either natural or synthetic) to add the nutrients back into the soil. The numbers you see represented on fertilizer packages and containers correspond to these 3 nutrients. The first number representing Nitrogen the second number representing Phosphorus and the third number Potassium.
Nitrogen stimulates early spring growth and helps to promote deep green colour as well as root, stem and leaf growth. Without nitrogen plants cannot grow.
Symptoms of Nitrogen deficiency: overall plant growth will be slow or stunted with lower older leaves turning to yellow, followed by browning then dying.
Sources of Nitrogen: blood meal, fish emulsion, fish meal, cottonseed meal, soybean meal and alfalfa meal are also good natural sources. Plants such as legumes get their Nitrogen from the atmosphere. They then fix that nitrogen in the soil for use by future plantings.
Phosphorus is essential to seed development, disease resistance and plant growth. It is necessary for producing sugar during photo-synthesis and it encourages root growth, flower and fruit production. It also strengthens stems, helps in resistance to pests and diseases and increases the rate of vegetable crop maturity.
Symptoms of Phosphorus deficiency: plant growth will be stunted, foliage will appear dull with reddened undersides and fruit and flowers will be small or few.
Sources of Phosphorus: bone meal is an excellent source of phosphorus as is rock phosphate. Try to stay away from super phosphate as it contains harmful salts that can cause an imbalance in your soils micro organisms. Phosphorus breaks down very slowly and can take years to move through the soil down to the root level where it is needed (it travels at a rate of about 1” per year). Therefore it is best to dig your phosphorus into the soil well before planting or apply it to the bottom of your planting holes.
Potassium helps to regulate a plants metabolism and contributes to early growth, stem strength, hardiness, vigour, good flower colour and disease resistance. It is essential for the proper development of root crops.
Symptoms of Potassium deficiency: leaves turn yellow at the tips and between the veins. Leaves tend to curl under then dry black or brown spots appear in the yellowed areas. Fruits may become deformed and yields may be low.
Sources of Potassium: seaweed, cocoa bean hulls, manure, compost, dried banana peels, wood ashes and granite dust.
The second group of soil nutrients are classified secondary MACRONUTRIENTS. They include: Calcium (Ca), Magnesium (Mg) and Sulfur (S)
While each of these soil nutrients are essential to your plants health, there are usually enough of them in the soil so fertilization is not always necessary. If you suspect a nutrient deficiency you may want to have to have your soil tested before you begin adding these nutrients.
Calcium is essential not only for healthy plants but also for balancing soils chemistry. Calcium helps to unlock other nutrients and any imbalances with this nutrient can cause imbalances with other nutrients.
Symptoms of Calcium deficiency: Terminal buds die; older leaves become dull and the leaf margins turn brown; the edges of younger leaves develop a light green edge; stems become weakened.
Sources of Calcium:Dolomitic lime, gypsum, crushed oyster shells, egg shells and superphosphate, Potassium-Magnesium Sulfate, Mg Chelates, Magnesium Oxide/Magnesia (low solubility)
Is essential for leaf and protein production. It is essential for photosynthesis and helps to activate many plant enzymes needed for growth.
The soils most likely to be deficient are sandy soils. Excessive amounts of calcium or potassium in the soil can lock magnesium up creating a temporary deficiency. Adding more magnesium isn’t the answer. Either of these conditions causes the soil to be to alkaline. Correcting the alkalinity by adding sulfur is the best way to fix this temporary deficiency. An excess of magnesium will lock up potassium, zinc, boron and manganese. It can also interfere with soil structure making it sticky.
Symptoms of Magnesium deficiency: The classic deficiency symptom is interveinal chlorosis of the lower/older leaves. However, the first symptom is generally a more pale green color that may be more pronounced in the lower/older leaves. In some plants, the leaf margins will curve upward or turn a red-brown to purple in color. Full season symptoms include preharvest leaf drop, weakened stalks, and long branched roots. Conifers will exhibit yellowing of the older needles, and in the new growth the lower needles will go yellow before the tip needles
Yellowing between the veins of older lower leaves, starting at the leaf tips and proceeding toward the middle, followed by browning and dying; leaves are thick and brittle; plants are stunted and produce little new growth.
Sources of Magnesium: Dolomitic limestone, epsom salts, sulfate of potash-magnesia soil minerals (and according to the U.S. Geological Survey magnesium is found in over 60 minerals),
Promotes root growth and seed production, and helps to maintain a dark green colour; it helps with vigorous plant growth and resistance to cold; and it is also used to acidify soil. Sulfur is slowly released from organic matter by microbial activity.
Symptoms of Sulfur deficiency: Yellowing of older leaves without browning and dying; stems are slender and brittle.
Sources of Sulfur : Gypsum, epsom salts, elemental (agricultural) sulfur, rain water, organic matter
The remaining 7 soil nutrients are classified MICRO NUTRIENTS. They include:
Boron (B), Copper (Cu), Chloride (CI), Iron (Fe), Manganese (Mn), Molybdenum (Mo), Zinc (Zn)
Even though these nutrients are used in very small amounts they are non-the-less all essential for plant growth.
Sources of Micronutrients: Organic matter is an excellent source of micro nutrients. Spreading a layer of compost or manure every spring will usually provide adequate amounts of all of these nutrients. Deficiencies are more likely to occur on sandy soils, acid soils with abundant rainfall or in very alkaline soil. Correcting soil pH is the key to unlocking these nutrients. Other sources of micronutrients are liquid seaweed, granite dust, chelates of the mineral and rock phosphate.
Photo Credit: This photo/slide was created by the author.
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For photos: Kimberley Pacholko 13 Essential Soil Nutrients For Plant Health – Horticulture For Home Gardeners
For content: Kimberley Pacholko 2021, Ornamental Garden Specialist, 13 Essential Soil Nutrients For Plant Health – Horticulture For Home Gardeners