Macro Nutrients Explained

Macro Nutrients
and their role in plants

Plants are bio-factories. In order for these factories to work/manufacture, they require raw materials such as: Light, Oxygen, Hydrogen (Water), Carbon Dioxide and Nutrients (both macro and micro). In this article we will be taking a closer look at the macro nutrients such as Nitrogen, Phosphates, Potassium, Calcium, Magnesium and Silicon. It is important for gardeners to be able to identify any nutritional disorders and how they can be rectified. A quick liquid nutrient reference guide can be found at the end of the article for different systems and growing mediums.

N – Nitrogen

Nitrogen is a unique element, as plants are able to take up nitrogen in the form of an anion (a negatively charged molecule) or a cation (a positively charged molecule). Plants are able to take nitrogen in as NO 3 or Nitrates and NH 4 Ammonium. Plants require or consume more nitrates than ammonia. A well balanced nutrient solution will have less than 10% of available nitrogen in the form of ammonia. Nitrogen has many functions in the plant; it is found in proteins, chlorophyll, protoplasm and plant hormones.

Source – All premixed nutrients will have adequate nitrogen levels. If a grower wishes to give his plants extra nitrogen in the vegetative stage then he can use Cal Mag Plus at a rate of 1-2 teaspoons (5-10ml) per gallon. This will supply the plant with 25 – 50ppm extra nitrogen, which will be more than adequate. Using Cal Mag Plus will also supply the plant with extra Calcium, Magnesium and Iron. If a grower wishes to use an organic source of nitrogen then they can use Mexican Bat Guano. Note that only 1% of the 10% of nitrogen in Mexican Bat Guano is readily available to the plant, the other 9% will slowly be released over a few weeks as the organic nitrogen is broken down. Bat Guano cannot be used in NFT or aeroponic systems; it will also have a limited affect in ebb and flow and drip systems. Bat Guano is ideal for soil growers.

Deficiency – Growth is slow, sparse and spindly the older leaves turn yellow and will eventually dry out and die. The complete leaf will turn yellow, with no green veins.

Toxicity – The plants will produce excess foliage that will be dark green. The plants will also be softer, disease and insect outbreaks will be severe (this will be due to a weaker softer plant). The root system will also be underdeveloped. High nitrogen levels can also retard flowering and fruiting, lower fruit quality and decrease yields as flowers don’t set. Nitrogen deficiency and toxicity is rare and will not be a problem if growers use premixed nutrients and follow the directions for these nutrients.

P – Phosphorus

Phosphorus is a very important nutrient for plants. It is required by seedlings, newly rooted clones and flowering and fruiting plants. Phosphorus is essential for the development of healthy roots, stimulation of flowering, ripening of fruits and seed production. Phosphorus is also required for the hydrolysis of starch to sugar and for the synthesis of starch to sugars (also known as energy transfer).

Source – Again, premixed nutrients will have adequate phosphorus for general plant growth. Plants will need extra phosphorus when they begin flowering and fruiting. This is why growers must change from a vegetative formula to a flowering formula. The flowering formulas will have higher phosphate and potassium levels to help stimulate flowering, fruiting and seed production. This all culminates in higher yields and better tasting produce. Taste is increased because of higher synthesis of starch in to plant sugars. For a grower to really boost their yields of flowering and fruiting crops it is advisable for them to use a blooming enhancer. Bloom Blaster, Monster Bloom, KoolBloom and PK 13/14 are all products that will boost phosphorus and potassium levels. These flowering and fruiting enhancers must be used from the second week of flowering onwards. Bloom Blaster and Monster Bloom can be started as late as 3 weeks before flowering and must be applied at a rate of 1 teaspoon (5 grams) per 5 gallons of water. KoolBloom should be applied at ¼ teaspoon per gallon or 1¼ teaspoons per 5 gallons of water. PK 13/14 must be applied at a rate of 1¼ teaspoons (5ml) per gallon of water. For organic growers in soil, Jamaican Bat Guano can be used at a rate of 2-3 (10-15 grams) tablespoons per gallon of water.

Deficiency – Plants are stunted and the leaves turn dark green to purplish in color. This is due to a buildup of Anthocyanin pigments. These symptoms normally occur in the older leaves first. Plant maturity will also be delayed and yields will be low. Seed production is also severely affected.

Toxicity – Phosphorus toxicity is very difficult to diagnose. Excess phosphorus will cause deficiencies of calcium, iron, copper and zinc. This will cause confusing signals as other minerals may be showing signs of deficiencies even when adequate amounts of these minerals are present.

K – Potassium

Potassium is the catalyst in plants. It is important for the manufacture and transport of plant sugars/carbohydrates, increases the chlorophyll in leaves, regulates the opening and closing of the leaf stomata, disease resistance, water uptake and ripening process of fruits. Potassium is also found in the juice of fruits which contributes to an increase of fruit taste and fruit quality.

Sources – The sources of potassium are the same for Phosphorus above.

Deficiency – Symptoms occur in older leaves first with yellow blotches and in severe cases dead spots will occur. Branches and stems will weaken and eventually becomes brittle. Flowering and fruiting is diminished and yields are low and poor in quality.

Toxicity – leaf margins may burn in sever cases, but often it will effect the uptake of magnesium and magnesium deficiencies will occur.

Ca – Calcium

Calcium is as important as N, P and K. Calcium is required in the roots, stems, leaves and fruits of plants. It is found in every cell wall and is required for the absorption of nitrogen.

Sources – Most nutrient solutions will have adequate calcium for general plant growth. If a grower is using reverse osmosis water then they should seriously consider using Cal Mag Plus. An application rate of 1-2 teaspoons (5-10ml) per gallon of water is sufficient to rectify any deficiencies.

Deficiency – Flower bud development is retarded, thus reducing yields, and fruit size is decreased. Roots die, leaving the plant open to root rot attack. Young leaves show symptoms before older leaves. The leaves can be deformed, and have yellow blotches which later turn into dead spots.

Toxicity – No visual symptoms; may cause magnesium deficiency.

Mg – Magnesium

Magnesium is found in the chlorophyll molecule. If a deficiency of magnesium occurs then magnesium is transported from the lower leaves to the new leaves. Magnesium uptake is affected by the concentration of potassium. If high levels of potassium are applied then the amount of magnesium should increase e.g. at the second week of flowering when blooming enhancers are used then Cal-Mag Plus should be applied.

Sources – Most nutrient solutions will have adequate amounts of magnesium. If a grower is using reverse osmosis water then Cal-Mag Plus (1-2 teaspoons per gallon) should be used as all the magnesium in tap water is removed by the RO process. For plants that are just beginning to show signs of magnesium deficiency then Green Stay can be applied as a foliar spray (1 teaspoon per quart) with Penertrator (2oz per quart) or added to the nutrient mix (1 teaspoon per gallon).

Deficiency – Older leaves (lower half of the plants’ leaves) show signs of yellowing. The yellowing occurs between the leaf veins which remains green.

Toxicity – There are no visual symptoms for magnesium toxicity.

Si – Silicon

Silicon accumulates mostly in the epidermal cells of a plant. It is also found in other cell walls. Silicon helps creates hardier, stronger plants and also increases the dry matter content of crops. It has also been known to increase the plants resistance to fungal attacks and also increases the plant's tolerance drought or under watering.

Sources – Dyna-Grow Pro-TeKt, Botanicare Silica Blast (potassium silicate), Dutch Master Silica and General Hydroponics Pyrosol are all good sources of silicon. Growers should take care when using this product as it will increase the pH of the nutrient solution, thus the grower will need to add pH Down to bring the pH back to 5.8 - 6 for hydroponics and 6.5 - 6.8 for soil.

Deficiency – Deficiencies of silicon have been known to reduce yields.

Toxicity – Not known.

Nutrients for different systems

Aeroponic Systems
Only the highest quality nutrients should be used for aeroponic systems. These nutrients cause the least amount of blockage in fine sprayers.

Suggested Nutrients