What do the different Macro and Micro Nutrients Do?

Every grower knows that plants need nutrients. A rich soil may be able to supply everything that a plant needs. Otherwise, the nutrients will need to be provided by adding them to the feed water. If you are using a high quality nutrient then it should be well-balanced and should contain everything that a plant needs and deficiencies should be uncommon. However, there are certain circumstances where they can still occur. This is usually down to one of the following:

  • The pH of the medium is not in the correct range. This means that certain elements cannot be uptaken by the plant
  • The water is unusual. For example, if it is very hard then it may contain an unusually high level of calcium. This could lock out magnesium and potassium and other nutrients.
  • Using Reverse Osmosis (RO) water with a nutrient that is not designed for it. This may mean that there will be a shortage of calcium and magnesium.
  • Soil has a tendency to absorb phosphorus and not release it. This can cause a phosphorus deficiency. The particular microbes in Mammoth P can help to solve this problem making the absorbed phosphorus available again.

If you suspect that you have a particular deficiency, The Canna Mono Range has individual nutrients in different bottles. Canna Trace Mix may help solve a micronutrient problem.

There are 3 different groups of nutrients:

The three groups of nutrients are macronutrients, secondary nutrients and, finally, micronutrients. They are all required by plants but in different quantities. The names just describe the amounts that they are needed in.

There is another attribute that is sometimes used to describe nutrients and that is either “mobile” or “immobile”. Nutrients are taken in by plants and transported within themselves to where they are needed and then used. The difference between mobile and immobile nutrients is that once mobile nutrients have been used, they can be still be relocated and reused within the plant if needed. Once immobile nutrients have been used they cannot be relocated and reused.

It is useful to know whether a particular nutrient is mobile or immobile because of the way a deficiency in it affects the plant. If the plant has a shortage of a mobile nutrient, it will generally take and move it from the lower leaves and shoots in order to be used for the new growth. This means that in the event of a scarcity, it will manifest in the lower growth first and then move upwards. In the event of a shortage of an immobile nutrient the opposite happens. Because the plant cannot take it and move it to be used for new growth, the deficiency will manifest itself in new growing shoots and leaves (particularly at the top of the plant) first.

The Macro nutrients. These are so-called because they are required in relatively large amounts by plants:

  • Nitrogen (N) mobile
  • Phosphorous (P) mobile
  • Potassium (K) mobile

The Secondary nutrients. These are not needed by plants in the same quantities as the Macro nutrients, but a fair amount of them are still required:

  • Calcium (Ca) immobile
  • Magnesium (Mg) mobile
  • Sulphur (S) immobile

The Micro nutrients. These are only required in small amounts, but they are needed:

  • Iron (Fe) immobile
  • Manganese (Mn) low mobility
  • Boron (B) immobile
  • Molybdenum (Mo) mobile
  • Zinc (Zn) mobile
  • Copper (Cu) immobile
  • Chlorine (C) mobile
  • Sodium (Na) little used and only by a few species of plant
  • Nickel (Ni) little used

So, all of the above elements are required by plants for optimum growth and health. There is something called “Leibig’s Law of the Minimum” which states that plant growth is limited by the availability of the scarcest element. For example, if all the required elements except Iron were in plentiful supply, and Iron was in short supply, then it would be the scarcity of Iron that would be the limit on the plant growth:

Leibigs Barrel - Illustration of how yield is compromised by nutrient lockouts
How yield is reduced by the availability of only the scarcest nutrient that is in short supply.

So, plants need all of the essential elements above in varying amounts. But what does each of them do? What does a deficiency look like and how can it be fixed? What does an overdose look like?

Here we’ll take a look at each nutrient and answer those questions:

The Macro Nutrients

Nitrogen (N)

What it does – Nitrogen is part of the chlorophyll molecule and is also needed to make amino acids which are the building blocks of proteins and DNA molecules. It is usually taken up by plants in the form of nitrate or ammonium. It is needed through the whole life of the plant but in proportionally larger amounts during veg.

Deficiency – While the plant is making leaves and populating them with chlorophyll, a lack of Nitrogen will slow down growth. The leaves will become yellow and eventually fall off from the bottom of the plant progressing upwards. New leaves become stunted and lack lustre. The plant may go into premature flowering and yields will be compromised.

In Excess – Leaves will turn dark green moving from the bottom to the top and will often form a “claw” with burnt tips. The stems and the leaves become weak. Too much nitrogen can delay the onset of flowering. If the excess continues into flowering then the final crop will almost always have an undesirable “grassy” aroma or taste.

Read more about nitrogen here

Phosphorus (P)

What it does – Phosphorus is used in the energy processes of plants (and animals too). It is essential for photosynthesis, respiration as well as energy storage and movement around the plant. It is also involved in growth and various other processes. It is usually taken up by plants in the form of phosphate (P2O5). Like nitrogen and potassium, It is needed in relatively large amounts throughout the lifetime of the plant but, in terms of ratios, even more is required during the flowering and fruiting stage.

Deficiency This often shows itself with dark blue or reddish purple leaves and stems, particularly on the lower parts of the plant. The plant becomes weak, Vertical and lateral growth slows. Dark copper blotches turning to bronze appear on lower leaves. They may contort, wither and drop. In the later stages, a deficiency will cause a reduction in the size and quality of the final crop.

In Excess – Calcium, magnesium, zinc & iron get locked out, leading to signs of a combination of deficiencies. Leaves have thin blades, and may have tip burn. Internodes are short. The final crop will probably have a harsh, chemical taste

Read more about phosphorus here

Potassium (K)

What it does – The last of the “Big 3” is Potassium and it plays a lot of roles. It has a positive impact on the immune system and disease resistance, drought resistance, enzyme activity, protein and starch (carbohydrate) production, root growth, and (particularly) crop quality. It is absorbed mostly as a cation (K+).

Deficiency – A potassium deficiency can usually be identified by rusty-brown leaf edges, beginning on the lower leaves first as they become pale. Stem branching may increase but the stems are often weak and scrawny. Immunity to diseases and drought are compromised and final crop size and quality will be reduced. Wilting may also occur.

In Excess – New leaves grow thin blades and become pale in-between the veins. Calciom, Magnesium, Zinc and Iron get locked out leading to signs of a combination of deficiencies. Lower leaves may develop spots and curl. Root tips may die back.

Read more about potassium here

The Secondary Nutrients

Calcium (Ca)

What it does – Although only needed in slightly lower amounts than the macro nutrients, Calcium is still very important for a number of different reasons. It improves the absorption and transportation of other nutrients around the plant. It also increases the activity of enzymes and is a key component in building cell walls. It is also key for a healthy immune system. In the soil it helps to prevent it becoming too acid. It is also used by microbes which perform a multitude of marvelous beneficial tasks.

Deficiency – A calcium deficiency can be caused by an over-abundance of magnesium (or potassium). These two secondary nutrients need to be balanced otherwise a deficiency in the scarcer one can be caused. Calcium does not easily move around a plant once it has been used. A calcium deficiency will cause slow leaf and root growth, and yellow-brown spots often appear on the leaves. The lower leaves contort and curl. Plant immunity to pests and (particularly) fungi decreases. A calcium deficiency in flowering can be especially disastrous as it makes the flowers of the plant highly vulnerable to botrytis and other molds. In fruit-bearing plants, like tomatoes, the weakened skin may develop something called “blossom-end rot”. This is not actually a disease but it does look just like a fungal infection. Providing the plant with adequate calcium , and preferably a silicon additive too, helps to safeguard against infections of most types.

In Excess – Growth can become stunted and leaves may wilt. Potassium, Magnesium, Iron and Manganese become locked out leading to signs of a combination of deficiencies.

Read more about calcium here

Magnesium (Mg)

What it does – Magnesium is the central atom in a chlorophyll molecule so without it plants would not be able to perform photosynthesis. It also assists with phosphorous uptake and activates certain enzyme systems. Unlike calcium, it is easily relocated around within a plant as required, even after it has been used.

Deficiency – A deficiency will usually affect the older, lower leaves first where there will be a loss of colour between the leaf veins (interveinal chlorosis) and rust-brown spots may appear.

In Excess – An overdose of magnesium causes stunted growth and very dark green leaves. It may appear a bit wilted which can occur when there are too many salts in the root-zone

Read more about magnesium here

Sulphur (S)

What it does – Sulphur plays many roles within plants and is a part of every cell. It is important for photosynthesis, hardiness, and for the formation of certain proteins. It is taken up by the plant in the form of sulphate (SO4). It is also important for transforming nitrate into amino acids.

Deficiency – Because of that last point, a sulphur deficiency is often mistaken for a nitrogen deficiency and vice-versa. Deficiency often manifests as yellowing in new growth, i.e. the younger leaves, whereas with nitrogen deficiency, the yellowing usually begins in the older, lower leaves. As deficiency gets worse, the leaves will begin to look withered and the stems can turn rather woody. In flowering, bud formation is slow causing reduced yields and quality.

In Excess – Like with a magnesium excess, an excess of sulphur will usually cause stunted growth and dark-green foliage. However, it will often cause burnt leaf tips and edges when the excess is severe.

Read more about sulphur here

The Micro Nutrients

Iron (Fe)

What it does – Iron is a part of many enzymes, and it is mainly involved with energy transfer around the plant and nitrogen usage.

Deficiency – A deficiency can be spotted by yellowing between the veins of leaves which has a sharper distinction than that caused by a magnesium deficiency. This starts at the back end of the leaves and progresses towards the tips, starting with the youngest leaves and progressing down to the older leaves which may eventually die and drop off. Overall growth is slowed down and yields will be affected.

In Excess – Too much iron can cause leaves to turn a bronze colour with dark brown spots appearing. Phosphorous uptake is reduced making it look like a deficiency in that vital element.

Read more about iron here

Manganese (Mn)

What it does – Manganese is a mostly used in the enzyme system in plants, particularly those involved with metabolism. It plays a role in chlorophyll production, photosynthesis, germination and maturation too. Manganese also helps with the uptake of phosphate and calcium.

Deficiency – A deficiency can be spotted by yellowing between the veins of younger leaves and sometimes brown/black specks. Eventually they can become almost completely yellow and then die and drop off. This pattern progresses down the plant to the older leaves. In soil, a higher than neutral pH can cause a deficiency.

In Excess – Young and new growth develop dark orange or rusty coloured patches. This progresses down the plant to the older leaves.

Read more about manganese here

Boron (B)

What it does – Boron is used for cell membranes which affect the structure and function of the cell. Boron helps plants (especially seedlings) survive stress. It is taken up by plants as BO3.

Deficiency – A boron deficiency can often first be spotted by dying tips on new growth and overall slightly stunted growth which looks twisted, contorted and abnormal. They may appear burned too. Dead spots appear between the leaf veins and the leaves can become brittle. Stems can become “corky” and rust coloured

In Excess – An excess of boron is very rare, but when it does occur leaf tips on new growth will turn yellow and then appear burned. Lower, older growth will turn yellow and eventually drop off.

Read more about boron here

Molybdenum (Mo)

What it Does – Molybdenum is vital for the production of enzymes which release the nitrogen from certain types of molecules. It is required to optimise plant growth.

Deficiency – Thankfully, molybdenum deficiency is rare in most growing circumstances and it is one you generally shouldn’t need to worry about. However, when it does occur, it can cause yellowing in older leaves which moves upwards through the plant. It can also sometimes cause rolled or cupped leaves and leaf-dropping.

In Excess – An excess of molybdenum can lock out iron, making it look like an iron deficiency. Also, leaves can become discoloured turning a greyish-brown.

Read more about molybdenum here

Zinc (Zn)

What it does – Zinc plays a part in protein and hormone production so it is very important micronutrient for proper functioning.

Deficiency – A deficiency causes very short internodes and stunting of plant leaves, particularly in the younger ones. Leaves exhibit interveinal chlorosis (yellowing between the veins) and they become misshapen. Final crop yield can be significantly reduced if zinc is in short supply.

In Excess – A zinc excess is very rare, but in severe cases when it happens the plant usually dies quickly. It prevents Iron from being used properly and the plant may look deficient in it.

Read more about zinc here

Copper (Cu)

What it does – Copper is another micro nutrient that’s involved in aiding the activity of enzymes which affect plant growth and the production of proteins as well as Vitamin A.

Deficiency – Without enough copper, plants can develop a bluish tint and leaves become thin and floppy. Eventually, the leaf edges can turn a copper-grey colour. Young leaves and shoots may wilt, become distorted and eventually die back. Growth and final yield is markedly reduced.

In Excess – Growth slows down and signs of an Iron deficiency may arise. Fewer branches grow and roots can die back.

Read more about copper here

Chlorine (Cl)

What it does – Chlorine is involved with the metabolism of the plant and water usage. It also assists the transport of calcium, magnesium and potassium around the plant.

Deficiency – A deficiency of chlorine (fairly rare) may manifest as a deficiency of calcium, magnesium and potassium. Leaf tips may burn and the edges take on a bronze colour. Young foliage turns pale green and wilts.

In Excess – An overdose of chlorine also turns leaves a bronze colour. Also, leaf tips and edges look burned. Growth is slowed. An overdose of chlorine looks very similar to a deficiency.

Read more about chlorine here

Sodium (Na)

What it does – Thankfully, plants need virtually no sodium, and most don’t need it all. Some plants use it to concentrate carbon dioxide and enhance the metabolism. It is one of those micronutrients that we really don’t need to worry about too much. However, if there is large amounts of it are in the root-zone, it could make it difficult for the plant to access other nutrients like potassium and calcium.

Read more about sodium here

Nickel (Ni)

What it does – This is another one of the micronutrients that is required in such small amounts that we really don’t need to be too concerned about it. It is used in minute amounts in making the enzyme which breaks down urea (which is one of the sources of nitrogen). As long as other forms of nitrogen are plentiful (as in ammonia or nitrate), a lack of nickel should not cause a problem.

Deficiency – Urea may accumulate in the plant which manifests as dead (necrotic) leaf tips

In Excess – nickel toxicity is incredibly rare but when it happens shoot and root growth become slowed and blotchy chlorosis can appear on the leaves. This is because iron, zinc or copper become locked out and signs of deficiency in these elements may appear.

A Non-Essential but Highly Beneficial Element

Silicon (Si)

Silicon is not actually essential to plants but is has so many beneficial effects on them that it would be almost negligent not to mention it here. Silicon helps to build strong cell walls. It improves plant structure by producing thicker, sturdier stems which can support the weight of more fruit or flowers. It also increases photosynthesis, and improves drought and disease resistance, particularly from fungal infections.

Read more about silicon here