How Potassium Helps Healthy Marijuana Growth

As with all plants, growing marijuana requires you to consider a number of factors before even getting started, not the least of which is nutrient balance. Whether you’re growing your weed outdoors or using an indoor hydroponic setup, carefully managing the nutrients your plants get is key to a healthy harvest.

This post discusses what role potassium plays in growing plants, why it’s important to keep it in good supply and ways you can incorporate it into your growing system.

How Potassium Affects Plant Growth in General

Plants need potassium for many different things including growth and development, pest control, and high fruit and flower production. This element is naturally present in soil, but is often deficient in most commercially-available soil types. The exception is some clay soils which can have potassium content levels as high as 3%. Each plant has slightly different nutritional requirements so it’s important to test your soil before planting.

Potassium is essential for the proper function of many plant processes including photosynthesis, water uptake and retention, and the transportation of nutrients throughout the plant. It’s even involved in enzyme function and the movement of nutrients into and out of cells. Potassium has also been found to enhance chlorophyll production and improve stabilization, which enables better conversion of light energy into energy.

Without adequate amounts of potassium, plants will weaken overall, which can lead to stunted growth, yellowing leaves and other problems. Not only will they be prone to disease, but even their physical structure will suffer. Too much potassium can also be harmful to plants, causing them to become overly lush and susceptible to disease. The right balance of potassium is essential for healthy plants.

Potassium’s Effect On Marijuana

Mariujuana plants need all the structural & circulatory support they can get, since they’re naturally tall plants. Potassium also affects cellulose production, which helps plants keep their shape and avoid collapse. This natural reinforcement also ensures that water doesn’t leak out of plant cells, thereby improving water retention in general.

Proper potassium levels can also improve cannabinoid and terpenoid yield, which are particularly important if you’re growing cannabis to make your own extract formulations (e.g. vape cartridges). It’s a good idea to peruse and research your target cannabinoid and terpene profiles before deciding on a nutrient regimen for your plants. Ethical terpene retailers like True Blue Terpenes make an excellent resource for preliminary research; you can find their selection of terpene strain profiles at

It's important to note that not all cannabis strains have the same nutrient requirements, meaning a feeding regimen that works for one cannabis variety won't necessarily work for another. While potassium is essential for any plant to live and develop, potassium shortages or toxicities aren't very common in cannabis plants.

Signs of potassium deficiencies or toxicity typically appear at around the third or fourth week of blooming, which is when most growers are especially vigilant. Remember that doing a soil test before feeding any supplemental nutrients is the best way to maintain proper levels.

Potassium’s Role in Cannabis Plants

Potassium is crucial for stalk stability as well as numerous essential functions in cannabis including photosynthesis. It’s also essential for the development and maintenance of the root system, which aids in protecting it from harsh, cold or hot weather and sufficiently grounding these vertically growing plants. Maintaining proper potassium levels for your strain can even increase bud size and density.

Seasoned growers understand that nutrient requirements change throughout a plant’s life. Let’s go over the changes in marijuana’s potassium requirements at each critical life stage:

Early Stage

It's best not to feed seedlings and cuttings since a lack of nutrition in the first 2-3 weeks of growth encourages healthy roots to develop. Feed your plant only when it has reached a height of 15cm. You may then begin by feeding it 25-50% of the recommended amount. As your plant enters the vegetative stage, gradually increase the supply to the full dosage.

Vegetative Stage

A cannabis plant has transitioned from the seedling stage to the vegetative growth phase by week 4. At this time, it will require significant amounts of nitrogen as well as other necessary nutrients in the appropriate ratios. When feeding commercial cannabis nutrients, follow the dosage recommendations carefully and only adjust if necessary.

Pre-flowering Stage

The pre-flowering stage occurs just before cannabis plants enter the flowering period and lasts for around 1-2 weeks. The pre-flowering phase is comparable to vegetative growth on steroids because some cannabis plants can sometimes grow up to two or three times their original height. Extra amounts of nitrogen, potassium, and calcium are required to support this accelerated growth period.

Flowering Stage

Most cannabis growers place more importance on how any nutrient affects the buds of the plant. Potassium can help increase the density, weight, and volume of the buds you produce.

During bloom, your cannabis plant will require more potassium. You'll generally boost potassium levels at the same time, or immediately after, boosting phosphorus and decreasing nitrogen during the end of pre-flowering (when the plant has stopped growing). The plant will be entirely concentrated on bud production from that point on. Extra phosphorus and potassium are going to be critical at this stage as these minerals significantly affect flavor, bud size, and overall development.

Ways to Provide Potassium

Potassium can be added to the soil through fertilizers or compost. You may also offer your plants a potassium-rich solution such as kelp meal or fish emulsion to drink if you’re using a water or gel growth medium.

Common Causes of Potassium Deficiency

Deficiencies can occur for a number of reasons. Below, we’ll discuss 3 of the most common causes growers run into and ways you can identify them.


Take a look at your lights before making any modifications to your growing medium or watering technique. You may accidentally be overheating the leaves with strong LED or HPS grow lights, especially if they’re brand new. Even if the temperature is cool, plants will display burn symptoms. To assess where the problem lies, move your plants away from the lights for a couple days and assess their condition.

Excessive Nutrient Supply

Excess fertilizers and nutrients may also cause plants to have yellow leaves or a sickly, droopy appearance. Plants grown indoors will have different nutrient requirements than those grown outdoors, so it's important to factor this into your regimen.

Nutrient Lockout 

Nutrient lockouts are the common cause of most deficiencies. Over time, mineral salts from feeding accumulate in growing containers and can throw off the pH level at the root. When the pH is too low, it makes the medium excessively acidic.

The optimal pH for potassium is between 6.1 and 7.1, meaning that if the soil's or water/nutrient solution's pH is too high or low, potassium uptake will either suffer or halt altogether. In this case, a flush is required to restore the pH to a healthy level.

Potassium Additives in Hydroponic Setups

Since hydroponic growth entails the plant roots being directly exposed to water flowing in a closed circuit, some might think they can skimp on potassium additives. But both veteran growers and studies confirm that sufficient amounts of potassium should be added to your hydroponic nutrient mix to ensure optimal growth for any plant. Luckily, it’s water soluble making thorough incorporation easy to achieve.

Individuals living in apartment buildings or condominiums are more likely to be inclined toward hydroponic setups, while homeowners typically lean more toward garage or gardening plots in states where cultivation is legal. In any case, the importance of potassium in plant growth cycles is well-established — and is deemed crucial regardless of the growing system you choose to experiment with.

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