Why Do Plants Need Potassium? Every Important Information     

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Plants need nutrients to grow, and potassium is one of the three macronutrients without which all greenery wouldn’t be able to survive. It works hand in hand with the other 2 macronutrients — nitrogen and phosphorus — in ensuring that plants grow and thrive. Potassium plays a critical role in plant development, and it’s best to always ensure that it is available to plants in the right amounts at all times. 

Plants need potassium to facilitate photosynthesis, a vital food production process. It also plays a crucial role in metabolizing food into energy for the plant to grow. Potassium also influences the absorption and movement of water and chemicals throughout the plant. 

In this article, I’ll discuss the harmful effects of inadequate potassium supply on plants, as well as the dangerous consequences of being overzealous with this essential nutrient. I’ll also cover the crucial roles of potassium, where it can be found, and how to ensure that plants are able to reap the benefits it offers. Let’s begin!

What Happens if Plants Don’t Get Enough Potassium?

Potassium is a critical factor responsible for plant growth. It is a macronutrient, which means plants need it in high amounts throughout their life cycle. Potassium plays a vital role in various aspects of a plant’s growth, such as enzyme activation, nutrient absorption, and photosynthesis. 

If plants don’t get enough potassium, growth is stunted, and photosynthesis is constrained. Potassium deficiency also reduces fruit and vegetable yield. Furthermore, an inadequate supply of potassium hinders plants’ other processes, such as root growth, respiration, and disease resistance.

Here are some telltale signs of a potassium deficiency in plants:

  • Leaves start to yellow or brown. The development of dead tissue typically begins from the margins of a plant’s lower leaves before moving slowly up. 
  • A reddish or purplish tint on the leaves. This is usually accompanied by browning on the leaf’s edges.  
  • Yellowish spots. These usually first appear along the margins of a plant’s older leaves. 
  • Blackening of the plant’s older leaves. This is usually confused with leaf burn, especially since the leaves take on the appearance of having been scorched. This is because plants suffering from potassium deficiency cannot efficiently use and regulate water. 
  • Stocky appearance. Plants may develop short internodes, producing visibly smaller new growth. Young leaves may take on a wavy look. 
  • Poor root health. The lack of potassium makes roots sparse, spindly, and not well-formed. 
  • Slow growth. Plants have varying growth rates. After some time, you can gauge just how much development you should expect from a specific plant. A decline in growth may indicate a nutrient deficiency.
  • Increased vulnerability to pests and diseases. Potassium deficiency makes plants incapable of defending themselves from the harsh effects of pest infestations and fungal infections. Often, plants can no longer bounce back after exposure to such conditions. 
  • Vines die back. Plant vines begin to wither. This is often misconstrued as an effect of pest infestation. 
  • Low resilience. Plants suffering from a lack of potassium have a hard time surviving winters and drought, periods when water and nutrients may become scarce or unavailable. 
  • Inability to bloom and fruit. Potassium deficiency can prevent plants from producing flowers and fruits. Slow growth may be observed, as well as frequent abortion of buds.

What Causes Potassium Deficiency?

Potassium deficiency is caused by poor growing conditions when the plant isn’t equipped with adequate amounts of this nutrient. Sometimes, potassium is available, but the plant cannot absorb it properly. Potassium insufficiency can also be caused by highly alkaline, acidic, or light, sandy soil.

Let’s break these causes down:

Unsatisfactory Growing Conditions

Just because potassium is often readily available to plants, this doesn’t mean that the greenery is always capable of absorbing it. Certain factors affect the ability of plants to take in this essential nutrient, and more often than not, it’s up to the gardener to ensure that the conditions are met. Sometimes, poor absorption can also be caused by the natural environment and varying weather conditions.

Here are some factors that may affect potassium absorption by plants:

  • Low soil moisture
  • Inconsistent watering
  • Extremely low temperatures 
  • Oxygen deficiency
  • Poor root health
  • Poor soil aeration

Low Respiration Rate

Poor respiration is the main culprit in improper and inadequate absorption and transport of potassium throughout the plant. Respiration is the process involved in combining the sugars produced by photosynthesis with oxygen to produce energy essential to plant growth. Without sufficient energy, plants won’t be able to absorb potassium efficiently.

Soil pH

Soil pH is the measure of hydrogen (H) concentration in the soil. pH levels indicate whether the soil is neutral, acidic, or alkaline. Neutral soil has a pH level of 6.5 to 7.5. A pH level lower than 6.5 means that the soil is acidic, while a pH above 7.5 means that the soil is alkaline (basic). In general, a higher pH level equips the soil with a greater capacity to make potassium available for plants to absorb. 

Light, Sandy Soil

When the soil is too light, sandy, or chalky, potassium (and any other nutrient) is easily washed away. In this case, adequate and consistent fertilization is best to ensure that plants can enjoy the benefits associated with potassium.

Clay soil is best capable of holding in potassium and other nutrients within its structure for plants to absorb. However, it isn’t always the ideal choice for all types of plants since clay soil often promotes waterlogging. This is a condition wherein too much water is in the ground, specifically around the plant’s root zone. This results in poor respiration, where oxygen exchange is inhibited. Quite literally, the plant will be unable to breathe correctly.

One of the most apparent signs of waterlogging in plants is water pooling on the soil’s surface.  However, sometimes, soil conditions may look ideal on the outside because waterlogging may occur deep around the root level. Unhealthy roots may lead to the death of the plant since it will no longer be able to absorb water and nutrients from the soil. 

The keys to avoiding the risks involved with waterlogged plants are soil amendments, such as coco chunks, compost, or shredded leaves. These promote better drainage and help significantly improve soil quality.

Potassium Explained 

Potassium, denoted as K, is classified as a macronutrient (along with phosphorus and nitrogen) essential to the development and growth of plants. Without it — or even due to the scarcity of it — plants may wither away and die. Macronutrients are nutrients needed by plants in large quantities. Otherwise, the latter miss the chance to achieve their full potential. 

Potassium is also classified as a mobile nutrient since it travels throughout the plant during its life cycle. However, not all forms of potassium can be absorbed by plants. Uptake of potassium only occurs when it is in a form that contains positively charged ions (K+) — also known as “cations.”

Roles of Potassium

Potassium plays various functions in plant development, growth, and survival. It’s essentially one of the backbones of proper plant nutrition. As a macronutrient, it must be made available consistently and in large quantities. 

Here are some of its most crucial roles:

Movement of Water and Nutrients 

Water and nutrients must be adequately distributed throughout the plant to ensure its growth and development. This guarantees that nourishment is effectively distributed to the different parts of the plant. Potassium is the only nutrient that remains intact and moves throughout the plant in a water-soluble form. It doesn’t integrate with other elements to produce compounds like proteins or carbohydrates. 

Regulates Stomata Functions

The opening and closing of the stomata (pores found in the leaves and stems) facilitate the transfer of oxygen, carbon dioxide, and water vapor. Potassium accumulates in the stomata’s guard cells, influencing them to open or close, causing them to swell (open) or become flaccid (close). Essentially, the stomata regulate water loss and allow the plant to breathe. 

Maintains Turgor

Turgor pressure is what makes the plant rigid through the adequate distribution of water throughout the plant’s cells. It is a force regulated by osmosis that pushes plant membranes against the cell walls and is responsible for expanding cell walls when plants develop and grow. Turgor pressure also aids in proper stomata function. Poor turgor results in wilting.

Enzyme Activation

The production of adenosine triphosphate (ATP) is one of its most essential roles, necessary for regulating photosynthesis. Other vital enzymes that potassium activates are fructose and protein. These play crucial roles in ensuring that the different parts of the plants function efficiently and harmoniously to promote growth, resistance, and survival. 

Aids in Photosynthesis

Photosynthesis is the process where the plant harnesses energy from its environment. In simpler terms, It is a process where plants use water, carbon dioxide, and sunlight to create food. Food comes in the form of a combination of sugars and oxygen, which will later be converted into energy, which is essential for various plant functions. 

A plant’s enzymes and the stomata play crucial roles in facilitating photosynthesis. Potassium, in turn, aids in activating these enzymes and regulating the opening and closing of stomata. In essence, potassium plays a significant role in ensuring photosynthesis.

Reduces Respiration

The respiration process involves the plant’s natural ability to produce its own energy and food for survival. Essentially, this is when plants use carbon dioxide present in the environment to metabolize oxygen and the sugars they produce during photosynthesis. This “plant food” is later converted to energy to boost plant growth. 

Respiration takes place in a plant’s roots, stems, and leaves, while photosynthesis occurs only in the stems and leaves. The respiration process must be adequately regulated because excessive respiration results in energy loss. 

Root Growth

The health of a plant’s root system is crucial to its growth and development. It influences a faster rate of shoot growth. Root health is also vital in boosting a plant’s resistance to drought. Potassium encourages roots to grow robustly and deeply into the soil for maximum water and nutrient absorption. 

Promotes Flowering and Fruiting

Fruits and blooms are among the more obvious indicators that a plant is healthy. Not all plants are expected to produce flowers and fruits, but those that are will tell you that there is a nutrient deficiency if they fail to produce any of the aforementioned. 

Potassium deficiency, along with insufficiency in other macronutrients, can lead to plants not being capable of flowering and fruiting. The lack of potassium will make fruits and buds slow to mature and often abort due to unsustained energy levels. 

Promotes Plant Resilience

Insufficient potassium in a plant’s system will make it susceptible to pests and diseases. Plants suffering from this deficiency will also become vulnerable to the effects of varying weather conditions — drought, frost, and extreme heat will become unbearable, leading to premature wilting. 

Sources of Potassium 

Potassium can be made available for your plants in different ways, typically via the soil or fertilizers. Some plants react better to certain types of soil and fertilizers, while others do not discriminate at all with the soil or fertilizer used. 

Here are some reliable sources of potassium for your plants:


Soil is generally packed with potassium. However, it may not be in a form readily available to plants, especially since a lot of the potassium can be found in the rocks and other minerals mixed in with the soil. 

The rocks and minerals have to be disintegrated and worn over time so that potassium can be absorbed by plants. 90-98% of the potassium found in soil is held by these minerals, known as inorganic structural potassium.

There are also non-exchangeable potassium forms in the soil, found in minerals like smectite and vermiculite. They absorb potassium from the ground and embed it within their layers and onto their structural edges, making potassium relatively more available for plant uptake. 

The easiest potassium form that plants can readily absorb is known as exchangeable potassium or solution potassium. These are found on the surfaces of clay soils, particularly colloids. They can interact with other cations and become more readily available for plants. However, since this form of potassium is found on the soil’s surface, it is prone to be quickly drained away. 


When it comes to fertilizers, it is crucial to apply them consistently, in the right amounts, and at the best time. It is advisable to provide adequate amounts of potassium early on, while plants are still young, so they reap the maximum benefits of this nutrient. Follow the recommended application methods for your fertilizer of choice. Make sure to apply regularly, especially during the growing season, to maximize your plant’s potential.

Ready-to-use fertilizers may come in liquid and granular forms, and you can choose specific formulations ideal for your plants’ needs. Liquid fertilizers are easy to use and go directly into the soil. 

As a result, the effects will be felt faster by plants. On the other hand, granular fertilizers are more convenient to apply and are easier to store. They come in sustained-release, slow-release, or quick-release formulations to cater to various needs. 

There are also natural fertilizers you can use as soil amendments to help boost your plants’ potassium intake. Here are some of them: 

  • Vermicast. Also known as worm castings, this type of fertilizer is 100% natural and odorless. It is made up of mud, soil, sand, and other debris found in the ground that has passed through a worm’s body. Essentially, it’s worm poop.
  • Manure. This is a fertilizer made up of the urine and feces of domestic animals, with some amendments like straw and hay thrown in. It is an excellent source of macronutrients. 
  • Compost. You can turn your kitchen scraps, particularly fruit peels, into an effective fertilizer for your plants. It is a slow-release fertilizer high in potassium and contains substantial amounts of nitrogen and phosphorus. 
  • Burned cucumber skins. Surprisingly, these contain 27% potassium by weight, a higher concentration than the more common types of fertilizers. They are categorized as fast-release fertilizers, so you can be sure that your plants can reap the benefits immediately. 
  • Sawdust. It contains 2% – 4% potassium by weight and is a slow-release fertilizer. It is effective for up to 4 years. 
  • Wood ash. This is the residue from burning wood, so the nutrient content varies depending on the type and quality of the wood burned. On average, wood ash contains 3% – 7% potassium by weight. It is an alkaline, fast-release fertilizer, effective for up to 4 months. 
  • Sulfate of Potash Magnesia. This contains 22% potassium by weight in a water-soluble form. However, it isn’t a balanced fertilizer since it has no phosphorus or nitrogen. 
  • Kelp. It is a large, brown seaweed that grows in nutrient-rich water. It is a slow-release fertilizer, effective for up to 6 months. 

Is Too Much Potassium Good for Plants?

It is possible to have too much of a good thing, and this applies to plants and gardening too. Too much potassium is not good for plants. It impairs cell functions, prevents nutrient absorption, and hinders photosynthesis and respiration.

Potassium toxicity doesn’t happen too often because plants can generally regulate the uptake of nutrients throughout their system. Furthermore, plants have a natural ability to tolerate and counterbalance excess potassium absorption. They will simply use negatively charged particles — called “anions” — to counteract “cations” (potassium’s positively charged ions).

Normally, potassium levels in plants vary from 0.2 – 2.5%, but they can go as high as 3-8%. Excess potassium won’t immediately cause harm to plants, but consistent and prolonged potassium surplus can lead to serious side effects. 

The usual culprits for exposing plants to the dangers of too much potassium are the gardeners themselves. Keep in mind that soil is naturally rich in this essential nutrient, particularly clay soil. Well-meaning gardeners sometimes use excess fertilizers on their soil and plants, mistakenly assuming they will be doubling the benefits. 

Here are some of the most common side effects of excess potassium in plants:

Cation Competition

Also called ion antagonism, this occurs when too much potassium in the plant’s system prevents it from absorbing other vital minerals like calcium and magnesium. A nutrient imbalance will negatively impact fruit yield, limit plant growth, and impair root health.

When these side effects occur, the plant will wilt and eventually die. The changes will first be felt in older tissue, typically beginning from the lower stems and leaves before moving up to newer tissue.

Lipid Peroxidation

This is a harmful chemical reaction where free radicals are produced, which damage and eventually kill healthy plant tissue. It primarily affects the membranes and inhibits essential functions, such as the transfer of ions throughout the plant. 

Increased Electrolyte Leakage

Electrolyte leakage is a natural stress reaction from plants through which they lose essential minerals via their membranes. Plants react negatively to the pressures caused by an oversupply of potassium, as well as to drought, pathogen attacks, and hypothermia. 


Potassium is an essential nutrient for plants, as it helps them to develop, grow, and survive. It’s crucial in vital functions such as photosynthesis, respiration, and nutrient transport. Without it, plants will soon wither and die. On the other hand, too much potassium can also be harmful to plants, forcing them to react defensively to the oversupply.
This macronutrient can naturally be found in the soil and can also be offered to plants via fertilizers and natural soil amendments. Potassium must be maintained at adequate levels to ensure plants achieve their full potential.

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