Info on Macro and Secondary Nutrients

Plant Nutrients

Water and nutrient are carried through in the plants xylem. Plants require a approximately 16 different elements for healthy growth. Carbon, calcium, hydrogen, nitrogen, oxygen, phosphorus, potassium and magnesium are needed in large quantities and referred to as macronutrients. Iron, manganese, zinc, boron, copper and molybdenum are known as micronutrients or trace elements and are essential to plant health.


Macro Nutrients 

These are the nutrients most used by plants. Nitrogen, Phosphorus and Potassium are the nutrients known as macro nutrients and fertiliser products display the N-P-K rating of a fertiliser in this fashion. These nutrients are always displayed in the same order on packaging and they form the base of all plant nutrient blends


The essential nutrients nitrogen is one of the main elements responsible for the growth of the plant. A plant converts nitrogen to produce proteins and amino acids for new cell growth. Nitrogen is very mobile throughout the plant and it promotes the new growth at the expense of the old. A plant deficient of nitrogen will display a week new growth and a spindly stunted plant. A shortage of nitrogen is usually first visible in the older leaves which become yellow and the veins on the underside of the leaves turn a red/purple colour. Plants are liable to go to seed. An excess of nitrogen will usually affect fruiting.

Most plants love nitrogen particularly during their vegetative growth period and smaller amounts during fruiting. Nitrogen needs to be replaced regularly because it is prone to being washed away during watering and also because of replenishment while the plants are in a vegetative growth stage.

Nitrogen is involved in the following:

  • Regulates a plant’s ability to make proteins
  • Allows a plant to tie cholorphyll, proteins, vitamins etc together
  • Is essential in the production of chlorophyll, aminos, and enzymes
  • Mainly responsible for stem and leaf growth
  • Responsible for the vigour of the plant

Nitrogen is most active in the new growth and can be found in amongst others, Calcium Nitrate, Urea, Potassium Nitrate, Ammonium Nitrate, Bird Droppings, Blood and Bone. Always be careful as too much nitrogen can cause burning.

Nitrogen deficiency symptoms are as follows:

  • Older leaves yellow between the veins while the veins remain green
  • Older bottom leaves turn completely yellow
  • As a progression more leaves turn yellow and drop
  • Sometimes leaves develop reddish purple stems and reddish purple veins on the underside of the leaf
  • Younger leaves progressively get effected with yellow between the veins
  • In very severe case all leaves yellow and then drop

Nitrogen deficiency can be treated by fertilizing with a nitrogen fertilizer such as one of the above mentioned. You would expect to see an improvement within three to four days.

Nitrogen Toxicity symptoms are as follows:

  • Excessive lush growth
  • Thin and weak stems
  • Leaves prone to damage due to the lush growth
  • Tissue breakdown causes the plant to be less able to transport water
  • Roots are poorly developed
  • Leaves turn a copper colour and drop
  • Roots darken and then rot
  • Small flowers and less of them

Nitrogen toxicity is best treated by flushing the media with water or possibly a weak nutrient solution so that the nitrogen is literally washed away. Do not use a nutrient that contains nitrogen. Do not add nitrogen for a week so that the plant can take up the nitrogen in the media.


Phosphorus is a mobile element and is necessary for photosynthesis. It provides a mechanism for the energy to transfer through the plant and is involved in the plants vigour and seed production. Phosphorous reaches its highest concentrations in the root tips, growing shoots and vascular tissue.

Soils and media are often chemically bound with phosphates due to incorrect pH when the pH is outside of the range of 5.7 to 6.7.

Deficiency of Phosphorus:

  • Stunted growth and small leaves are a usual sign along with leaves turning a bluish green and often blotches appear.
  • Starting on the underside of the leaf, the main veins turn reddish purple, along with the stems and leaf stems although this may not always be well pronounced.
  • Older leaves turn dark and curl downward.
  • At a more advanced stage severely affected leaves form large purplish black blotches which later become a bronze purple and dry and drop off.
  • Flower buds are usually smaller and the plant is usually slower to flower with seed yield is generally poor
  • The plants become vulnerable to attack

Treatment of Phosphorous deficiency:

Check pH is in correct range and adjust if necessary

  • Fertigate with an inorganic fertilizer solution such as a hydroponic solution that contains phosphorous
  • When preparing soil add a balanced fertilizer that contains phosphorus.

Phosphorous Toxicity:

  • Signs of toxicity are generally those of a deficiency of another element such as magnesium, calcium, iron and zinc however the zinc is usually the most common. This is due to the fact that the phosphorous interferes with the uptake and stability of these elements.

Treatment of Phosphorous Toxicity:

  • Flush media with a low CF balanced fertilizer at least three times
  • In extreme cases flush three times with water.

Phosphorus is vital for photosynthesis and cell formation. It is a catalyst involved in transferring energy in the plant. Phosphorus is important in the formation of flowers and seeds and is important in developing root systems. Phosphorus is mobile and a deficiency shows in the colour of the leaf producing a deep green colour.


Potassium is responsible for activating plant functions, acting as a catalyst for enzymes to ward off disease and soils rich in potassium increase a plant’s resistance to diseases including mould. Potassium is involved in cell growth by division by combining sugars, starches and carbohydrates. It helps increase chlorophyll and regulate stomata openings thus making better use of air and light. Potassium is necessary for the production of proteins that augment the oil content which helps improve the flavour of fruit and vegetables and is closely linked to disease resistance and strong healthy root growth.

Deficiency of Potassium

A plant deficient in potassium displays a mottling of the old leaves and a yellowing between their veins. Potassium is mobile within the plant thus the older leaves will show the deficiency first. The plant can at first seem healthy but is susceptible to disease.

Progressive signs of Potassium deficiency:

  • Leaves of the plant are dark green and the plant appears healthy
  • Branching occurs but they are week
  • Leaves loose their luster
  • Margins of leaves turn grey and tunr a rusty brown
  • Leaves curl up and die
  • Older leaves become yellow and display rust coloured blotches and later drop
  • Mould becomes prevelant
  • Flowering is diminished and fruit drop occurs

Treating Potassium deficiency:

  • Potassium added directly to the nutrient mix is sometimes undertaken hwoever this can sometimes be difficult to achieve
  • Slowly increase the level of potassium in the nutrient
  • Generally foliar feeding with potassium is not recommended
  • In soil based crops added potash is the usual method however care should be taken to adjust the pH as potash is generally very alkaline.

Toxicity of Potassium:

Generally difficult to recognise as symptoms mimic those of others and generally are present when the plant is displaying deficiencies of other elements such as manganese, zinc, iron and magnesium.

Treating Potassium Toxicity:

Flush media with mild complete nutrient solution and if that is not successful a water flush maybe acceptable but not overly recommended.

Secondary Nutrients

Magnesium, calcium and sulphur make up the secondary nutrients and are also used in rather large amounts. Most general all purpose household fertilisers do not have enough of the secondary nutrients required for indoor house plants. Often secondary nutrients can be available in large quantities in the soil and or the ground water so before large additions these should be checked


Fast growing plants require large amounts of calcium and often require as much calcium as any one of the macro nutrients. In soils dolomite addition is a successful way of treating deficiencies. Deficiency thus displays first in the new growth where leaf tips tend to die back and new leaves show a brown to black scorching

Calcium supports the cell walls and is an important part of the plant root structure. It is not very mobile and is thus more concentrated in the older growth. Calcium is fundamental in cell growth and is responsible for cell integrity and membrane permeability which ensures proper flow of nutrients. Roots must have calcium present at their tips

Deficiencies symptoms of Calcium progression:

  • Young leaves turn a very dark green
  • Growth is slow and new shoots are discoloured
  • New shoots are mishapen, strivel and die
  • Bud development is very slow

Treatment of Calcium deficiency:

  • Add lime or dolomite to soil
  • Foliar feed crops using calcium chelate – be careful to trial an area first so not to cause damage to crop
  • Flush media with a well balanced nutrient blend
  • Check and adjust pH of media.

Calcium Toxicity:

Generally toxicity signs are difficult to see as they are masked by the deficiencies of others. Manganese, magnesium, iron and zinc deficiencies can be exacerbated by high levels of calcium. These elements can be present but become unavailable due to the high levels of calcium. High levels can also stunt growth particularly if applied during early growth of the plant. Excess levels in a hydroponic solution can cause precipitation and or cloudiness in the solution due to the reaction with sulphur


Magnesium is important for photosynthesis. A deficiency will produce yellowing of the plant leaves spreading from the centre of the leaf to the outer edges finally resulting in the leaf turning an orange colour. Magnesium is a carrier of phosphorus in the plant.Magnesium

Magnesium deficiencies are common particularly in low pH soils and medias. In the case of soil adding Dolomite before planting and on an annual basis helps significantly to reduce occurrences of Magnesium deficiency. In the case of hydroponic systems you should look at your pH and amount of Magnesium Sulphate used.

Magnesium neutralizes the toxic compounds produced by the plant. It is also essential for the absorption of light energy and thus vital to the production of chlorophyll. Magnesium aids in the manufacture of sugars and carbohydrates and the utilization of nutrients.

Deficiency is very common. Yellow patching between the green veins starts in the lower leaves and later spreads to the middle leaves. Further on in the stages rusty brown spots appear on the tips, margins an between the veins. Before dying the brown leaf tip curls upwards. In really severe cases the whole plant can display a whitish tinge before browning and then dying. A minor deficiency will cause little or no harm however it usually only preempts a more major deficiency and this results in a diminished harvest.

In soil the magnesium often becomes unavailable to the plant when the soil is too wet or cold and this often leads to the soil having too low a pH. The other issue regarding fast growing plants is that the root system is often not capable of supplying enough Magnesium to the plant. High CF nutrients can also impedethe take up of Magnesium due to the fact the water uptake is affected.

Dealing with Magnesium deficiency:

  • Addition of Magnesium Sulphate (Epsom salts – but make sure the grade is correct)
  • A 2% of Magnesium Sulphate solution maybe foliar fed to the plant
  • Continue adding Magnesium Sulphate until all the symptoms disappear.
  • Adding Dolomite can aid the situation – this also adds Calcium
  • Keep the root zone and even temperature of 20 to 25 degrees C
  • Reduce CF for a week
  • Keep pH in soil above 6.6 and in hydroponics above 5.8

Magnesium Toxicity

It is very unusual to have a toxicity level but very high levels can influence Calcium uptake. Drenching the media with water will decrease the level.


Sulphur is seldom deficient as most fertilisers contain some form of sulphur. It is seldom added to soil or media by itself and is generally added as magnesium sulphate. Sulphur is immobile and is a vital element in plant cells and seeds. It is an essential building block of many vitamins and hormones including Vitamin B and in its sulphate form buffers the pH of a solution. Al most all water contains sulphur in the form of sulphate and sulphate is involved in protein synthesis and is part of cystine and thiamine aminos. Sulphur is essential in the synthesis and breakdown of fatty acids and is involved in the creation of oils that provide the flavours of fruit and vegetables. Hydroponic nutrient solutions keep the sulphate elements separate from the calcium by placing the calcium in the ‘A” tank and the sulphates in the “B “ tank to avoid precipitation when the elemts combine to form a crude insoluble Gypsum or Calcium Sulphate which would settle at the bottom of the tank

Progressive signs of Sulphur deficiencies:

  • Symptoms similar to nitrogen deficiency
  • Older leaves turn pale green
  • Young leaves turn yellow to lime green
  • Leaf stems turn purple while veins remain green
  • Leaf tipscan burn and turn downeards while darkening
  • Leaves turn completely pale yellow
  • Interveinal yellowing follows
  • Elongated stems become woody at base.

Treatment of Sulphur deficiency:

Fertilise with a balanced hydroponic solution or fertiliser that contains sulphur. Check pH is between 5.5 and 6 and adjust as necessary. Inorganoic sulphur can be added to magnesium sulphate and applied

Sulphur toxicity:

Generally causes no issues providing Cf is relatively low while when CF is high it can have the effect of blocking other nutrients due to the fact that the plants takes up the sulphur and tends to disregard the other elements. Overall plants display smaller growth habits and dark green foliage. When severe tip burn can occur.

Leave a Reply