Discolored leaves are a major source of worry for all plant parents and no plant parent can escape the curse of yellowing or browning leaves forever. All plant problems are not caused by insects or diseases, some symptoms are an indication of nutrient deficiency or overload. Plant nutrient imbalances can often be seen as either discoloration of leaves or misshapen growth. These symptoms are unfortunately misread because the tell-tale signs are so common with other plant issues or are a combination of several issues.
So before you go about remedying nutrient issues in your plants, do check for pests under leaves, in between stems and other nooks and crannies. Changes in the colour of leaves can also be caused by soil that drains poorly, compacted root growth, soil that is too loose and does not retain moisture, irregular watering schedule with long spells of dryness in between waterings, too small a pot, and many such reasons. Extreme changes in temperature also affects plant growth and health.
Nevertheless, too much fertiliser can cause the plant root and shoot system to burn and too little can affect plant health and growth rate.
 

What Nutrients Do Plants Need?

Gardeners generally tend to discount the need for fertilisation of potted plants, comparing them to the plants growing in the wild and not needing any additional fertilisation. Plants growing in the wild grow directly in the soil, which is a part of the larger ecological system. The roots of such plants have direct access to decaying organic and inorganic matter, essential minerals through breaking rocks and rainwater stored underground and other organic matters such as insect and animal discharge. All these sources provide the plant with more than enough nutrients that ensure excellent growth that cannot be achieved in the isolated soil system of a potted plant, wherein the nutrients get depleted over time.
Plants require a few different kinds of nutrients to stay healthy and grow at a good rate. Nutrients that the plants need in larger quantities are called macronutrients, namely nitrogen, potassium, phosphorus, also known as NPK,  calcium, sulphur, and magnesium. Other nutrients required in comparatively lesser quantities, called micronutrients, include boron, copper, iron, manganese, molybdenum, and zinc.
 

How Do Plants Get Nutrients?

The major, and sometimes only source, of all these nutrients for plants, is the soil. The plants take up nutrients through the roots along with water. The transportation of these nutrients through various plant parts also happens due to water pressure and movement. Hence, along with a good supply of essential nutrients, the right amount of water is also very important.
One other major requirement for nutrient uptake is the right pH balance of the soil or the potting mix. Each plant prefers a specific pH range to be able to access the nutrients in the soil, soil that is too acidic and too alkaline disrupts normal functioning for the plants and affects plant health adversely.
Let’s take a look at the common nutrient deficiencies.
 

Common Nutrient Deficiencies

 

Nitrogen (N)

Nitrogen is a macronutrient required the most by plants. Plants absorb Nitrogen in the form of either ammonium or nitrate which is water soluble. This water soluble nature of nitrogen also means that it runs off with water every time the plant is watered and it comes out of the drainage hole. Nitrogen is essential for rapid growth especially for fruit and seed development. It is also essential for bigger leaf size and healthier foliage.
Deficiency symptoms: Chlorosis (leeching of chlorophyll) of the entire plant to a lighter green colour followed by yellowing of older leaves that then progresses to the younger leaves. Plants show poor growth with thin stems that don’t support plant weight and etiolation is also a visible sign.
 

Phosphorus (P)

Phosphorus is the second major macronutrient that the plant needs for a healthier rate of photosynthesis, protein formation, help with seed germination, bloom stimulation, and budding. Plants absorb Phosphorus in the form of phosphate.
Deficiency symptoms: Purple or bronze colouration on the underside of older leaves due to the accumulation of the pigment, Anthocyanin. Plants that are deficient in phosphorus grow slowly and have stunted growth.
 

Potassium (K)

Potassium is the third major macronutrient that is essential for making plant food and the formation of sugars for protein synthesis and cell division in plant and root development. It also increases the plant’s resistance to diseases. Plants absorb Potassium as an ion, which is water-soluble and can be easily leached and lost due to run-off from the soil.
Deficiency symptoms: Chlorosis along the leaf edge of new and matured leaves. This then progresses to interveinal scorching and eventually necrosis from the leaf edge to midrib. The chlorosis due to potassium deficiency is irreversible, nevertheless, the new growth will be completely healthy.
 

Magnesium (Mg)

Magnesium is a building block of the chlorophyll molecule and it is a key element to promote the function of plant enzymes to produce carbohydrates, sugars, and fats and also regulate plant metabolism and rate of nutrient absorption.
Deficiency symptoms: One major symptom is interveinal chlorosis in older and more mature leaves. If the deficiency progresses it leads to a decline in plant growth rate, reduction in leaf size and shedding of older leaves over time.
 

Calcium (Ca)

Calcium is a building block of the plant cell wall to provide structural support. It is an immobile component and stays in the older tissue throughout the growing season. The first deficiency symptom appears in younger leaves and growing leaf and root tips.
Deficiency symptoms: Any new plant growth, shoot or root has stunted growth. The younger leaves curl on themselves with browning of leaf edges and leaf tips with leaf tip burn. In some plants, calcium deficiency also manifests as extremely green foliage and the roots become short and stubby.
 

Manganese (Mn)

Manganese is an enzyme activator for nitrogen absorption and assimilation and is also required for photosynthesis, respiration, and enzyme reactions.
Deficiency symptoms: New leaves show interveinal chlorosis and necrotic leaf tissue. The new leaves also become smaller with growing deficiency and leaf tips can die.
 

Iron (Fe)

Iron deficiency manifests similar to that of Magnesium, except that it shows on young leaves and shoots instead of older leaves.
Deficiency symptoms: Light green to yellow interveinal chlorosis on new leaves and young shoots, which then progresses to shoot dieback. If the deficiency is not treated, the new growth shows reduced size with complete leeching of chlorophyll and necrotic leaf tissue.
 

Zinc (Zn)

Deficiency symptoms: Chlorosis, bronzing, or mottling of younger leaves, along with interveinal chlorosis in new leaves that progresses to reduced shoot growth.
 
Remedying nutrient deficiency can take time and the application of fertilisers at regular intervals is important to bring back the plant to prime health. Keep in mind to not over-fertilize the plants and give supplements at regular intervals. Once the plants are back to health, augment the soil by adding fresh organic matter every year. There are plenty kitchen hacks to help you maintain a healthy garden.
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