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Potassium Deficiency

May 7, 2020
How & When to Feed Your Plants

Potassium Deficiency in Cannabis Plants

Growing any plant, from flowers to vegetables, requires the grower to provide their plants with different nutrients throughout their growing cycle. The same is true for cannabis plants and providing them with the right amount of nutrients is critical to growing a perfect plant. The three major nutrients cannabis plants need are nitrogen, phosphorus, and potassium.

Each of these major nutrients plays a critical role in cannabis development, but not all at the same time. In the vegetative stage of growth, cannabis needs higher amounts of nitrogen to support leaf and stem production. During the flowering phase, phosphorus is necessary to strengthen stems, improve flower formation, and stimulate root development. Potassium is necessary during all stages of growth and growers must be sure their plants do not develop a deficiency.

The Role Potassium Plays in Cannabis Development

Potassium plays many critical roles in the growth and development of a healthy marijuana plant. It supports the process of photosynthesis, which gives the plant a rich green color and is vital to its health. It also helps the plant build a robust root system that is resistant to root rot and does not suffer during cold weather. This makes potassium an essential nutrient to monitor in outdoor plants, especially where the weather can be unpredictable.

Potassium also helps plants regulate water usage throughout the plant. With the right amount of potassium, plants will be resistant to periods of drought by being able to conserve and focus water on the most sensitive areas.

Signs of a Potassium Deficiency

Since potassium is such a vital nutrient to the healthy development of a cannabis plant, it is essential for growers to be familiar with the signs of a potassium deficiency. These signs include the following:

Discolored Leaf Tips

One of the first signs of a potassium deficiency is when you begin to observe yellowing of the tips of the leaves on your og kush or blue ice marijuana plant. The discoloration typically starts on older growth and affects younger growth as the potassium deficiency worsens. Eventually, the yellow tips turn brown and crispy.

This often looks similar to nutrient burn, which is an excess of nutrients that causes the plant to develop yellow, brown, and burnt leaf tips. However, unlike nutrient burn, a potassium deficiency causes the leaves to yellow in the margin between leaf veins.

Spots on the Leaves

The next symptom of a potassium deficiency is necrotic spots on the cannabis plant’s leaves. These spots will be brown and crispy like the edges of the leaves, eventually developing pale yellow or white spots as well. These spots indicate that the plant is producing an insufficient amount of chlorophyll, but the veins in the leaf will keep their green color.

Discolored Stems

As the deficiency worsens, other areas of the plant will begin to show signs of discoloration. The stems of your auto gorilla or auto gelato strain plants will turn a brownish red color, as will the petioles that connect the leaves on one branch.

Stretched Out Plants

Cannabis plants suffering from a potassium deficiency will stretch out and the stems become weak. Growers often mistake this symptom for increased growth, but the plants are not actually getting larger. In reality, the plant is stretching itself thin as growth is slowed down. Leaves will be much smaller, showing a more dangerous stage of potassium deficiency.

Causes of a Potassium Deficiency

It is important for growers to understand what causes potassium deficiency in their plants. It is worth it to note that canabis seeds grown hydroponically will generally not suffer potassium deficiencies. However, plants grown using other methods may experience potassium deficiency for any of the following reasons:

Salt Build Up

One of the most common causes of a potassium deficiency is actually providing too many nutrients. This is because the nutrient salts build up in the soil over time, and the excess salts prevent the plant from being able to absorb potassium.

Acidic Soil

Another common cause of potassium deficiency is the soil pH being too low, meaning it is too acidic. Acidic soil causes nutrient lockout, preventing the plant’s roots from absorbing any nutrients, including potassium.

Check Lighting

A common issue that growers sometimes mistake for potassium deficiency, particularly for indoor plants, is lighting. Growers using HPS and LED grow lights may overheat the leaves of their plants. Even if the temperature is cool in the grow room, the plants may exhibit signs of burning. It is important that growers eliminate this option before making any major changes to their grow medium or nutrient schedule.

How to Treat a Potassium Deficiency

Potassium deficiencies can halt plant growth and ruin a grower’s crop. When growers notice their plants are suffering from a potassium deficiency, they must act swiftly to correct it to avoid permanent damage to their plants. To treat a potassium deficiency in any of your i49 plants, growers can do the following:

Maintain a Healthy Soil pH

The most important thing a grower can do to address a potassium deficiency is check the pH of their growing medium. Soil should have a pH of 6.0 and 7.0 for optimal potassium absorption. Plants grown hydroponically or with coco noir should have a pH of 5.5 to 6.5

If the pH of the soil is too low, growers must first flush their plants’ root systems. They should use a neutral pH water until the acidity is back to a normal level. Once that happens, growers can start adding nutrients to their plants at half of the usual strength.

Water Plants Properly

Overwatering often leads to a potassium deficiency, as well as deficiencies in other vital nutrients. That is because overwatering causes the roots of the marijuana plant to rot, which prevents it from absorbing any nutrients. If growers notice the signs of overwatering, such as drooping plants with yellow leaves, they should resolve that problem before a potassium deficiency develops.

Overwatering plants can lead to mold growth as well. Mold growth has a similar effect on a plant’s ability to absorb potassium and can even infect other parts of the plant.

Check Nutrient Supplements

Many potassium deficiencies in cannabis plants are caused by an imbalance of nutrients. Growers must check the labels of their nutrient supplements to see how they interact with each other as some nutrients diminish the absorption of other nutrients. For example, nitrogen and calcium inhibit potassium absorption, so striking a healthy balance among these three nutrients is paramount to the overall health of a cannabis plant.

Use a Potassium Booster

Once the cause of the potassium deficiency is resolved, medical cannabis seed growers can give their plants potassium boosters to correct the deficiency. Potassium boosters often come with higher amounts of phosphorus, called PK boosters (or ‘bloom boosters’), and help to keep a healthy balance of all major nutrients. Plants in the flowering stage may need an even larger boost, as the potassium plays a critical role in growing large buds.

Popular potassium boosters include:

Wood Ash

Many growers prefer to use organic growing methods to cultivate their cannabis plants. For these growers, wood ash is an excellent option for a potassium booster. Wood ash contains between 5%-7% potassium, 1.5%-2% phosphorus, and 25%-50% calcium compounds, helping to boost potassium and keep a healthy balance of other major nutrients. 149 seed growers must be careful about the kind of wood ash that they use, as not all wood ash is beneficial to cannabis plants. Wood ash can be added to the top of the soil before watering. It is critical that there is no wind, as wood ash can be harmful to humans, animals, and the leaves or stems of cannabis plants.

Kelp Meal

Kelp meal is another popular potassium booster for cannabis plants. Kelp meal is rich in chelated nutrients and releases slowly over time, ensuring that plants are not inundated with more nutrients than they can absorb at once. Not only does kelp meal provide potassium, but it contains several other trace minerals that boost cannabis growth, including calcium, magnesium, iron, copper, and zinc.

To add kelp meal to cannabis plants, sprinkle it on the top of soil before watering. Liquid kelp meal can be used as a foliar spray to protect plants from hot and cold temperatures.

Bloom Boosters

There are many commercially available nutrient solutions that are specially formulated to meet the needs of cannabis plants grown from high thc or high cbd hemp seeds for sale at One of these nutrient solutions is called bloom boosters, and it is especially beneficial in treating potassium deficiencies. Bloom boosters are typically liquid and contain large amounts of phosphorus and potassium. They are meant to be added to the water used on cannabis plants periodically during the flowering stage. However, plants in the vegetative stage that are suffering from a potassium deficiency benefit from its use, as well.

The Bottom Line

Growers can expect to see their plants recover from a potassium deficiency within one week of treatment. If the problem is addressed early enough, there will be minimal long-term consequences. However, damaged leaves will never recover and should be removed.

Potassium deficiencies have the potential to ruin the health and vitality of a cannabis plant. Growers must know the signs and take immediate action to correct the problem. With the right care and treatment, growers will have the five-star cannabis plants of their dreams.

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