Potassium Deficiency Cannabis & How to Fix it

If you've noticed some unhealthy changes in your cannabis plants recently, and you've ruled out both calcium deficiency and magnesium deficiency — is it potassium? Potassium deficiency is another nutrient issue that can sometimes escape even the most experienced growers' attention until plants are visibly suffering.

Cannabis potassium deficiency is commonly confused with light burn, stress, or other nutrient deficiencies. Light burn happens when plants are under overly-intense light fixtures, and triggers the same onset of symptoms.

You may also see similar signs of potassium deficiency if you've recently transplanted, overwatered, or otherwise stressed out your plants. So how can you tell if it's a real potassium issue?

The Role of Potassium in Growing Cannabis

Potassium (K) is the third principal nutrient noted on the label of fertilizer products (N-P-K). In plants, it plays a crucial role in maintaining structural integrity, called the turgor pressure. The turgor pressure of individual cells helps keep plants upright and prevents wilting.

In addition to providing the ingredients for a structurally strong plant, potassium helps plants "breathe." Plant leaves have special cells lining the undersides called stomata, which open and close to release vapors and gases. Without potassium, this process doesn't function properly, and it negatively impacts photosynthesis.

Finally, potassium activates biochemical enzymes, which helps the plant express waste materials.

What Are the Signs of a Potassium Deficiency in Cannabis?

Many nutrient deficiencies appear quite similar to the signs of stress. Some of the very same signs and symptoms you might recognize from other stressful situations (overwatering, light burn, repotting) will look remarkably similar to those of a potassium deficiency. Once you've ruled out all of the above, the crispy burnt edges of your plant's leaves might be a result of a potassium issue.

The visible signs of potassium deficiency in cannabis are:

  • The tips of leaves turning brown and looking slightly burnt.
  • Burnt edges will coincide with yellowing around the edges of fan leaves.
  • The veins on the interior of the leaves remain green, no matter what colors the rest of the leaves turn.
  • Plants have distinctly stunted growth, compared with average growth expectations.
  • As the condition worsens, leaves begin to fall off.

How to Fix a Potassium Deficiency in Soil?

If you are working in a soil-based grow room, it's likely you already have enough potassium for your plants. The deficiency might have more to do with the ability of the plant to absorb the available potassium, rather than not having enough available. 

The first step of addressing a potassium deficiency is to eliminate all other possible causes. Any of the signs stemming from a stressful experience for the plant will slowly disappear on their own (so long as they are not re-exposed). For example, if you think the burnt leaves come from a light burn, address the light intensity (or location) and examine the plant again in a few days.

The second step is to test and rebalance the pH level. If you are growing in a system anywhere outside the 6.0 to 7.0 pH range, it could inhibit the plant's ability to absorb nutrients, including potassium, properly. 

Flush the system, using neutral ph water. Then slowly reintroduce nutrients. 

What types of nutrients are you using? What's the best way to boost potassium in the soil, if you aren't using fertilizers designed for cannabis? Once the pH is back between 6.0 to 7.0 ph, add either potassium nitrate (available at garden stores) or wood ash and manure for organic grow rooms. Sparingly additional potassium, as too much can increase the salinity of the soil, which would cause disruptions to other nutrients.

How to Fix a Potassium Deficiency in a Hydroponic System?

In a hydroponic system, it's much the same process. The signs and symptoms of potassium deficiency will appear in much the same way, from the same root causes. Once you've totally ruled out other possibilities for the defoliation and burnt leaf tips, you'll want to test the system for pH level.

Just like in soil pH level will impact a plant's capacity to absorb enough potassium. Check the system's pH level. Ideally, when working in a hydroponic setup, you'll want to aim for between 5.5 to 6.5 for the best results.

If the system is too basic or too acidic, flush the system with pH-neutral water. Give the plants a few days to recover before slowly reintroducing cannabis-specific hydro fertilizers back into your hydroponic setup. This allows the plants to readjust. Over the coming days and weeks, check new plant growth for improvements.

A Final Word on Potassium Deficiency in Cannabis

Right alongside nitrogen and phosphorus, potassium is a necessity for all plant life. As a grower, you need to know both the signs of cannabis potassium deficiency but also how to rule out other potential issues. 

While a true deficiency is rare, there may be issues making it difficult for your plant to adequately absorb enough from the environment. Taking pH and all nutrient levels into consideration can help quickly, and confidently address a true deficiency. And what happens if your plants are suffering from a lack of potassium? When caught early on, a potassium deficiency will have little impact on the final flower.

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