NPK Ratio & Nutrient Balance In Plants

You have likely seen the NPK ratio on the bottle of nutrients you purchased or are shopping for, but are you aware of how the ideal plant nutrient ratios change throughout the plant’s life cycle?

If you aren’t already aware, nutrient balance is one of the most important factors affecting your plant health, quality, and yield.

There are many different schools of thought on which NPK ratio is best across the different stages of growth.

Growers constantly try and manipulate their feeding schedule with additives and supplements to tweak nutrient balance. We'll cover why this is not a great idea.

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NPK Ratio & Nutrient Balance In Plants


You have likely seen the NPK ratio on the bottle of nutrients you purchased or are shopping for, but are you aware of how the ideal plant nutrient ratios change throughout the plant’s life cycle?

If you aren’t already aware, nutrient balance is one of the most important factors affecting your plant health, quality, and yield.

There are many different schools of thought on which NPK ratio is best across the different stages of growth.

Growers constantly try and manipulate their feeding schedule with additives and supplements to tweak nutrient balance. We'll cover why this is not a great idea.

General information on plant nutritional requirements

Before we take a deep dive on nutrient ratios, we want to quickly cover the basics of plant nutrition for those who are unfamiliar.

Macronutrients (primary nutrients)

There are three essential nutrients plants need in relatively high quantities - Nitrogen, Potassium, and Phosphorus. These make up the NPK ratio you’ll find on your bottle of nutes.

Nitrogen is responsible for producing robust, leafy growth. This is why you’ll see it in higher ratios during veg, and it will fall off during flower.

Phosphorus does the opposite, helping your plants develop flowering sites and produce large buds. Traditionally, growers would ramp up the phosphorus during flower because of this.

Potassium, on the other hand, isn’t necessarily veg or bloom specific. Instead, it helps regulate a variety of plant functions, including strong root growth, increased resistance to disease and increased water intake, along with thick, sturdy growth.

There are specific ratios of these nutrients across the different stages that we believe to be the best. We'll cover these later on, but we need to talk about secondary nutrients now.

Secondary nutrients

There are secondary nutrients that are also essential, but in lower quantities. Some of the most important include magnesium, calcium, and sulfur.

Magnesium and calcium go hand in hand, and are often an area where plants become deficient. Magnesium helps aid in the uptake and utilization of other nutrients, along with producing carbs and sugars to help during flower.

Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants.

Sulfur helps produce chlorophyll, and plays an essential role in foliage and root development.

Micronutrients

Finally, there are micronutrients. These are nutrients that are still incredibly important for plants, but in very small quantities. 

Many base nutrients contain some level of micronutrients, and most nutrient packages come with a micronutrient supplement to help round out the nutritional profile of your plants. Here are some of the most important:

  • Zinc (Zn)
  • Manganese (Mn)
  • Iron (Fe)
  • Boron (B)
  • Chlorine (Cl)
  • Copper (Cu)
  • Molybdenum (Mb)
  • Silicon (Si)

If you want to learn more about the basics of plant nutrition before getting to the advanced topic we are about to cover, check out our complete guide on nutrients and pH

This will give you an above-average understanding of plant nutrition, along with the role pH plays. But, let’s get into the main topic today: important nutrient ratios72 across different growth stages.

Distinguishing between deficiency and nutrient imbalance

When looking at plant issues, its easy to assume you are deficient in a nutrient and attempt to remedy the issue by feeding heavier.

Your plant might show signs that its starving for potassium, and you think more nutrients is the answer.

But, this will only make matters worse, causing you to burn your plants. There is a strong likelihood the culprit is actually nutrient imbalance.

To understand this concept better, let’s look at Mulders chart.

This shows how nutrients interact with one another. Nutrients interact either antagonistically or synergistically.

They can increase the uptake of one another. Or, they will fight among each other and can lock each other out if the balance/ratio is off.

So by feeding your fertilizer heavier, you are just creating a bigger imbalance, while risking burning your plants.

So before you assume your plant needs more fertilizer, check the EC of your solution and your runoff.

You can also determine if you are experiencing a nutrient imbalance by looking at your media for buildup. This is a sign that a nutrient is locked out, and building up in the soil rather than being taken up by the plant.

Once you rule out the possibility of underfeeding, you can consider adding a supplement to make up for the missing nutrient.

Why NPK ratio changes over different plant stages

It makes sense when you think about why the ideal NPK ratio would change from propagation, to early veg & late veg, and then throughout flower.

The plant is trying to accomplish different goals in different stages. At first, the main objective is strong root development. So, you’ll need an NPK ratio with higher levels of nitrogen.

As your plant starts to veg, nitrogen levels will increase as the goal becomes robust, leafy growth with horizontal branching and tight internodes.

Finally, when it comes time to flower, the goal is obviously producing dense, potent flowers. Nitrogen levels will drop off as phosphorus needs increase.

We’ll now cover our recommendations of the ideal plant nutrient ratios during each stage. There are many differing schools of thought on what is best, though. They will vary across the particular strain being grown, nutrient source, your plants ability to actually take up nutrients, etc.

Important plant nutrient ratios across different growth stages

Like we said earlier, there are many different schools of thought as to which nutrient ratios during veg and flower produce the best results. 

But, we have evidence that suggests you should stick with a nitrogen to potassium ratio of 5:4, or 1:1 during veg. Then during flower, drop this down  to a ratio of 2:3.

You may be wondering how phosphorus factors in. After all, it is one of the three nutrients associated with NPK. But we’ve come to realize that phosphorus may not be needed in as high of quantities as we once thought.

Research has shown that your plant can take up all it needs during late veg and early bloom. After that, its just about keeping phosphorus levels sufficient, and more is not better.

Another study revealed that excess phosphorus during flower will lead to ultra-dense popcorn nugs. So, don't make the mistake of thinking more phosphorus will lead to bigger flowers!

As you can see from the chart above, phosphorus needs remain pretty low throughout the plant's life cycle.

When it comes to secondary nutrients, the calcium to magnesium ratio we believe to be the best is 3-5:1. This high calcium ratio will result in charge balance and ideal uptake and utilization of the nutrients throughout the plant.

There are a few micronutrient ratios we feel are important as well. Try and stick with products that contain twice as much iron as manganese and zinc, and four times as much iron as copper and boron.

If you go back and look at Mulder’s chart above, you’ll see that iron affects the uptake and balance of these four other micros, so ensuring the ideal ratios is important.

Which nutrient package provides the best balance?

The best one we’ve seen as far as nutrient balance goes is the General Hydroponics Flora Series, as they do a great job of providing nutrients in the right ratios. 

It was first formulated backing 1976, and relies on science to produce the ideal formulation. Flora Series provides consistent performance and unparalleled results for your best crop yet.

It consists of the ideal balance of all three types of nutrients: primary, secondary, and micronutrients.

Big takeaway about nutrient balance and ratios

We know a lot of this seems overwhelming. The reality is, you may not ever achieve the ideal nutrient ratios. 

If you are using a 2 or 3 part nutrient formulation, there are so many different nutrients jammed into those bottles that perfection is just unrealistic.

A lot of growers prefer these smaller nutrient packages because they are simple and easy to use, but they will never provide the perfect nutritional balance because they are too broad.

That’s why we recommend using a full-fledged, comprehensive nutrient package with a deep, complex feeding schedule.

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