Cannabis plants need three nutrients above all.
Nitrogen, phosphorus, and potassium.
A deficiency (or an excess) in any one of these nutrients can have drastic consequences.
Today we are going to look at the third one of those nutrients: potassium.
What does a potassium deficiency in weed plants look like and what do you need to do to fix it?
Keep reading to find out. We will also cover the most important aspect of this topic: how to prevent a potassium deficiency in the first place.
- 1 Potassium Deficiency In Weed Plants
- 2 Potassium Deficiency In Marijuana Plants: Final Thoughts
Potassium Deficiency In Weed Plants
To understand the effect of a potassium deficiency on your harvest, we need to first understand what potassium does and why it is necessary for your plants.
Potassium (often referred to as “K” by growers, due to its symbol on the periodic table) plays a vital role in all stages of growth of your weed plants.
When your weed is growing in soil with a sufficiently high level of potassium, it is better able to resist bacteria and mold. K increases the strength of the roots which is necessary for water uptake and disease resistance.
The mineral also facilitates cell division which is needed for the growth of plants. It helps sugars, starches, and carbohydrates combine with each other and increases chlorophyll to regulate stomatal opening in the leaves.
This is necessary for the plants to make better use of light and air. Your weed plants also need potassium for the synthesis of proteins which augment the oil content and improve the flavor of the cannabis.
Without sufficient potassium, your marijuana plants suffer. This results in a number of symptoms.
Symptoms Of Potassium Deficiency In Weed Plants
Potassium-starved weed will appear healthy initially. However, it is extremely vulnerable to disease. Symptoms of potassium deficiency in weed include:
- Older leaves are usually affected first while the new leaves remain healthy. The leaves may start developing spots around the margins and tips. Slowly, the entire leaf is affected. It becomes yellow and dies.
- The plant’s stems also become weak and brittle.
- If the deficiency is minor, the leaves may still look alright and the plant may even grow tall. But the tips and edges of the bottom leaves will start to darken or develop tan or brown necrotic spots.
- As the deficiency becomes more pronounced, the leaves lose their luster. New branches may appear but they will be scrawny and weak.
- As more and more potassium is depleted, the leaves develop chlorotic spots (faded or tan spots). You might see mottled spots of red or yellow between the veins. Stems and petioles may become red.
- If the plants are in the vegetative stage, more severe deficiency may result in slower growth. A severe potassium deficiency will cause the leaves to be smaller. Larger fan leaves will become necrotic and turn brown at the margins before dying off.
How To Identify Potassium Deficiency In Cannabis Plants
Here are some early signs that can help you identify a potassium deficiency in your weed plants:
- Since potassium deficiency causes the internal temperature of the foliage to climb, the protein cells burn and degrade. This degradation is rapid at the edge of the leaves, so this is where maximum burning occurs.
- Plants may appear healthy with dark green foliage initially, but the leaves soon lose their luster.
- Leaf margins may turn grey and curl up
- Yellowing of older leaves and they may have rust-colored blotches
- Since your plant cannot resist disease, rot may set in.
- Flowering is retarded and greatly diminished.
Causes Of Potassium Deficiency In Cannabis Plants
The causes of potassium deficiency in weed plants will differ based on the media you use for growing.
- K deficiency is commonly seen in outdoor soils and planting mediums which lack this vital nutrient.
- Low soil oxygen levels also result in potassium deficiency. Usually, lower oxygen in soil is a result of soil compaction or excess moisture. Transplanting, too much heat, and overwatering can also result in low oxygen.
- Too much calcium and magnesium in the soil can also cause a potassium deficiency, since those minerals prevent both nitrogen and potassium from being absorbed.
- If you use hydroponics, then reverse osmosis water is a possible cause of potassium deficiency, since it does not contain any nutrients.
- A high pH can also impact potassium levels, because it prevents the roots from being able to absorb the nutrient.
How To Fix A Potassium Deficiency In Marijuana Plants
Again, the way to fix potassium deficiency will differ, based on the media you use. Here are some tips.
- In a hydroponic setup, you need to recalculate your solution’s content and change it. Some growers add potassium sulfate or potassium chloride directly to the growing solution.
- For soil media, use a fertilizer with N-P-K (nitrogen phosphorus potassium). You could choose from organic or chemical fertilizers. Make sure that the chemical fertilizers are suitable for edible plants.
- How much potassium you add depends on the product you choose. Read the label carefully and follow the instructions on the packet. It is best to start small and go from there.
- You can also add organic seaweed mulch, granite dust, or greensand to fix a potassium deficiency. Some growers add organic fertilizers like bloodmeal, cottonseed, alfalfa, fish emulsion, guano, animal manure, etc. These contain potassium balanced with phosphorus and nitrogen.
- Wood ash or soluble potash mixed with water can help with potassium deficiency too. However, this has a pH of over 10. You would need to lower it to around 6.5 with a pH-lowering mixture before adding it.
It is important to closely watch the leaves after starting treatment.
Preventing Potassium Deficiency When Growing Weed
Here are some steps you can take to prevent a potassium deficiency from occuring in the first place.
- Use high-quality soil. Most growers use loamy soil. Loam contains a mixture of sand, silt, humus, and clay. It provides vital nutrients and also encourages drainage. This prevents oxygen depletion which is crucial for preventing potassium deficiency. Fertilize with a complete N-P-K (nitrogen phosphorus potassium) fertilizer.
- If you’re using a soilless medium for growing weed, use coco coir.
- If using hydroponics, make sure to start with clean pH-neutral water. As soon as you suspect a potassium deficiency, act fast. Flush the system using clean water with proper pH.
- In the case of soil media, make sure the soil pH is 6-7. For hydroponics or coco coir, the pH should be 5.5 to 6.5.
- If you are using grow lights, move them away from the plants.
- Use homemade banana peel tea to not only treat and prevent K deficiency but also fatten up the buds. To make this tea, soak chopped banana peel pieces in water and let the solution sit in the refrigerator for 3-5 days. Filter the tea, dilute it with water, and add this K-rich solution to your plants.
Potassium Deficiency In Marijuana Plants: Final Thoughts
A potassium deficiency in weed plants can have devastating effects on your harvest. And unfortunately, it is not always easy to spot a deficiency in this nutrient, much less the cause of one.
Hopefully this guide has helped you determine if your cannabis plants are suffering from a lack of potassium. And if so, helped you fix it.
And looking toward the future, hopefully the tips above will make potassium deficiencies a thing of the past altogether. Now that you know how to prevent this common weed growing problem, you will hopefully never have to worry about this issue again.