NPK Ratios In Cannabis Fertilizers: Balance Your Soil

Ever heard of NPK Ratios? As it turns out, understanding the nitrogen, phosphorus, and potassium levels in your soil can help you grow bountiful cannabis plants.

Perhaps one of the most important factors to a successful grow is the soil and fertilizer. That’s where NPK ratios come in. You have to nail the PH level of the soil for your cannabis plants to thrive. You’ll want to get that PH level between 6.0 and 6.8. Getting your fertilizer right presents its own massive challenge. To make the most of your fertilizer, you need to understand the ins and outs of what is commonly referred to as NPK.

What is NPK Fertilizer?

NPK stands for nitrogen (N), phosphorus (P), and potassium (K). These are the three most important nutrients in fertilizer. They play a vital role in plant growth and development. The letters found on a container of fertilizer tell us the ratio of these nutrients in the fertilizer, while the numbers represent the amount of nutrients present in the fertilizer.

• Nitrogen (N) – Nitrogen promotes the healthy growth of leaves.
• Phosphorus (P) – Phosphorus promotes root growth and helps develop strong buds.
• Potassium (K) – Potassium supports the overall function of how plants grow.

Before the plants are harvested, it is recommended to flush them. Flushing helps remove nutrient buildup, allowing your plants’ full flavor profile, aroma, and potency to come out. This step can be done by stopping the use of any nutrients during the last two weeks of growth. You can also use water to flush the nutrients out of the soil and maintain good NPK ratios.

What is a good NPK Ratio?

As an example, a container of fertilizer with a label that reads 3-1-1 is 3% nitrogen, 1% phosphorus, and 1% potassium. According to Amsterdam Genetics, “Roughly speaking, NPK ratios of 3:1:1 are best for any cannabis strain throughout the growth stage. Once the plants start to flower, nitrogen percentages should be lowered as potassium and phosphorus levels increase. Early flowering calls for a 1:3:2 ratio; late flowering requires 0:3:3 instead.”

During the vegetative phase, NPK ratios of 3:1:1 are recommended.  The nitrogen in the plant’s fertilizer helps to build a strong leaf structure. A strong leaf structure is used in photosynthesis to help the root system grow, leading to flowering, which is where the beautiful buds come from.

When plants reach their early flowering stage, the recommended NPK goes to 1:3:2. Increased phosphorus levels help establish a strong root system, while the potassium increase helps meet the needs of the growing plant.

As cannabis plants begin to finish approaching the late part of the flowering cycle, the recommended NPK is 0:3:3. Most cannabis plants take an average of 120 days or more from seed to harvest. However, this can change depending on the strain being cultivated.

How to Test Your NPK Ratio

You don’t need to be a scientist to tell if something is wrong with a cannabis plant. Cannabis plants talk to you when they grow. They tell you what they want and expect you to give it to them. When you ignore them or neglect them, it shows.

Some knowledge is needed, however, to identify and correct issues or at least how to research various problems that might arise. Namely, when a nutrient deficiency or proficiency is present, it’ll show in the plant’s leaves. 

Understanding how to tell when your NPK ratios are off is essential to the growth of your cannabis plant.

If nitrogen levels are too low plants will show signs like pale or lime green colored leaves, yellowing, curling of leaves, premature falling off of leaves, fewer branches, poor yields, and more. Too much nitrogen, and you can see plants start yellowing, becoming droopy, producing poor bud formation, and becoming eagle-clawed.

If phosphorus levels are too high, you’ll see brown leaves and a dying plant triggered by a condition known as nutrient lockout. When this happens, the plant stops receiving nutrients, including the proper amounts of micronutrients like copper, iron, zinc, etc. If those phosphorus levels get too low, lower leaves on the plant will begin to look shiny and display hues of dark blue, grey, or green. You may also see purple veins and curling of leaves.

If potassium levels are too low, you’ll notice burnt leaf edges, curling of leaves, and frail, weak stems. Plants with low potassium levels are at a high risk of becoming infected with pests and pathogens. If plants make it through to harvest, they will produce a very poor yield or poor-quality cannabis. If potassium levels are too high, you’ll see signs like interveinal chlorosis, dark spots, and curling of lower leaves.

Beyond these visual signs, you can also test the NPK levels of soil at home using some basic science. Oregon Agriculture in the Classroom has a great way to test soil NPK levels at home. You can also purchase analog or digital meters to test soil NPK levels starting at around $15.

When cannabis plants have the right environment and the right NPK ratios, they will let you know. You‘ll see beautiful leaf color, strong stems, gorgeous bud structure, and pest-resistant plants that produce great yields of high-quality potent bud.

Final Thoughts

Growing cannabis can be fun. It can also be a real challenge. Yes, it grows like a weed, but what many people leave out is it grows like a very moody, temperamental weed. Choose the wrong environment and things get out of hand quickly. 

Thus, if you have followed this guide and your NPK levels seem optimal for successful plants, something else could happen. Here are some other things to keep in mind when raising the most happy, healthy, and bountiful cannabis plants:

Fresh, clean air is a must. This means being free from pests like mites and aphids and pathogens like mold and powdery mildew. Using filtered air is highly recommended.

The right amount of light is also essential. Too much light and you will burn your plant’s leaves, stunting their growth, possibly even killing them. Not enough light, and they will not grow right. You’ll end up with frail, weak plants that produce little to no buds.

By optimizing your fertilizer and avoiding common cannabis growing mistakes, you are on your way to being a skilled grower. Don’t lose hope or be discouraged if things do not turn out perfectly with your first cultivation and harvest attempt. Growing your own cannabis plants takes practice, and you might require some trial-and-error to get the process just right. At least with this guide in hand, you NPK levels can be less of a challenge to get just right. 

Frequently Asked Questions

What does NPK stand for in fertilizer?

NPK stands for nitrogen (N), phosphorus (P), and potassium (K). These elements are the most important nutrients in fertilizer. These letters can be found on a container of fertilizer, and the labels can also tell us the ratio of these nutrients in the fertilizer.

What is the 20-20-20 rule for fertilizer?

Besides listing the NPK content on a fertilizer, ;labels for fertilzers often contain numbers that represent the amount of nutrients present in the fertilizer. 20-20-20 means that the fertilizer has a balanced of equal parts nitrogen, phosphorus, and potassium. These ratios are especially ideal for growing cannabis plants in poor quality soils by providing a high amount of each of these three essential plant macronutrients.

How to use NPK fertilizer?

Before using your NPK fertilizer, it is best to mix the fertilizer into water and then water the plants evenly with the mixture. This ensures that the nutrients are distributed evenly in the soil, which is best for the plant’s health.