Plant growth doesn’t depend on fertilizer quantity alone — it also depends on whether the plant receives a complete set of nutrients, and whether those nutrients are in a form the plant can actually use. Too much of certain elements can create an imbalance, while a deficiency in even a single element can affect leaves, roots, flowers, or yield.

Understanding what nutrients plants need — what the primary nutrients are, and how secondary nutrients differ from micronutrients — is therefore fundamental, both for plant care and for fertilizer product development. This article explains the role of each nutrient group, along with guidance on choosing fertilizers and plant biostimulants that better match a plant’s actual needs.

What Nutrients Do Plants Need?

Essential Plant Nutrients

Plants require a total of 17 essential elements for growth. Of these, 3 come from air and water — carbon (C), hydrogen (H), and oxygen (O). The remaining 14 are obtained from soil, water, fertilizer, or growing media, and are divided into three groups based on the amount plants need: primary nutrients, secondary nutrients, and micronutrients.

This grouping doesn’t mean one group is more or less important than another — it simply reflects the quantity plants require. Even though micronutrients are needed in tiny amounts, a deficiency can still disrupt important processes inside the plant.

Differences Between the Three Nutrient Groups

Good nutrient management should consider all three groups together, rather than focusing only on N-P-K — a plant may have sufficient primary nutrients but still lack certain secondary nutrients or micronutrients. Knowing what nutrients plants need helps in choosing nutrients that better match a plant’s actual requirements.

What Are Primary Nutrients, and What Do They Do?

Nitrogen, Phosphorus, and Potassium

Primary nutrients refers to N-P-K — the elements plants need in the largest amounts compared to other nutrients, and typically the main numbers listed on a fertilizer label.

• Nitrogen (N) promotes leaf and stem growth and chlorophyll formation. A deficiency often shows up as yellowing of older leaves, while excess nitrogen can weaken the plant and cause it to over-invest in leaf growth.

• Phosphorus (P) plays a role in root development, energy transfer, flowering, and seed formation, making it important during both the early growth stage and the reproductive stage.

• Potassium (K) helps regulate water balance, nutrient transport, stomatal function, and overall plant strength, and also contributes to yield quality.

Although all three belong to the same group, this doesn’t mean plants need them in equal proportions at every stage. Once you understand what primary nutrients are, choosing a primary-nutrient fertilizer and an appropriate formula should also take the plant species and growth stage into account.

Managing Primary Nutrients

Managing primary nutrients shouldn’t focus only on the numbers in a fertilizer formula — it should also consider plant species, growth stage, soil characteristics, moisture, and soil test results together.

For example, during a stage when a plant is pushing leaf growth, it may need a higher proportion of nitrogen, while during root development, flowering, or fruit development, the phosphorus and potassium ratio may need to be adjusted to match that goal.

Approaches worth considering:

• Split fertilizer applications over time rather than applying a large amount all at once
• Monitor soil moisture alongside fertilizer application
• Check soil pH, which affects nutrient uptake
• Observe how the plant responds after fertilizing
• Use soil or leaf tissue analysis when necessary

The core of managing primary nutrients isn’t about maximizing fertilizer volume — it’s about choosing the right type, amount, and timing to match the plant’s actual needs.

What Are Secondary Nutrients, and Why Shouldn’t They Be Overlooked?

Calcium, Magnesium, and Sulfur

Secondary nutrients are those plants need in amounts second to N-P-K — namely calcium, magnesium, and sulfur — but they play specific roles that other nutrients can’t fully replace.

• Calcium (Ca) strengthens cell walls and supports the growth of shoots, young leaves, and root tips.

• Magnesium (Mg) is a key component of chlorophyll, so it’s directly involved in photosynthesis.

• Sulfur (S) plays a role in forming amino acids and proteins, as well as certain other compounds within the plant.

Despite being called “secondary,” this doesn’t mean they’re less important. If a plant is receiving enough N-P-K but still isn’t growing well, checking whether secondary nutrients are sufficient — and considering a secondary-nutrient fertilizer suited to the plant’s needs — is another area that shouldn’t be overlooked. Understanding what secondary nutrients are helps in diagnosing plant problems more thoroughly.

Signs That May Relate to Secondary Nutrient Deficiency

Calcium deficiency may show symptoms in the shoots or young leaves, while magnesium deficiency commonly appears as yellowing between the veins of older leaves. Sulfur deficiency may cause young leaves to turn pale or yellow and slow overall growth. However, these symptoms can resemble problems from disease, root damage, over- or under-watering, or improper pH — so the cause shouldn’t be judged from leaf color alone.

What Are Micronutrients, and When Should They Be Used?

Micronutrients Plants Need

Micronutrients are elements plants need in small amounts, but they’re important to various internal processes such as enzyme function, chlorophyll formation, pollination, and the uptake of other nutrients.

Essential micronutrients include:

• Iron (Fe)
• Zinc (Zn)
• Boron (B)
• Copper (Cu)
• Manganese (Mn)
• Molybdenum (Mo)
• Chlorine (Cl)
• Nickel (Ni)

Even though only small amounts are needed, a deficiency can still affect growth or yield quality. Knowing what micronutrients are is therefore useful for selecting nutrient supplements that target the specific problem.

Use Micronutrients with Care

Micronutrients should be used in appropriate amounts, because the effective concentration range for plant use is fairly narrow — since plants need only small quantities. Using more than needed can cause toxicity to the plant. The gap between the amount a plant needs and the amount that becomes excessive is quite narrow, so overusing micronutrients can lead to plant toxicity.

Before use, consider:

• Plant species and observed deficiency symptoms
• Existing nutrient levels in the soil or growing medium
• Soil pH
• The chemical form of the nutrient being used
• Application method — soil, water, or foliar

Are Plant Biostimulants Necessary, and How Do They Differ From Fertilizer?

The Role of Plant Biostimulants

When considering whether plant biostimulants are necessary, it’s important to clearly separate their role from that of fertilizer. Fertilizer is used to directly supply nutrients to plants, while biostimulants are typically used to support certain physiological processes — such as root development, recovery after stress, or improving yield quality.

Biostimulants should not be used as a substitute for fertilizer, pest control products, or proper management of soil, water, and the root system. Instead, they should be a supporting tool used once the basic conditions for plant management are already in good shape.

Products in this category may include seaweed extracts, amino acids, humic–fulvic substances, organic compounds, or various other bioactive substances, each with different properties and mechanisms. The results therefore depend on the type of substance, concentration, application rate, growth stage, environmental conditions, and the plant’s condition at the time.

How Is This Different From “Fertilizer”?

The key difference is that fertilizer supplies the nutrients plants need — such as nitrogen (N), phosphorus (P), potassium (K), as well as secondary nutrients and micronutrients — to support growth and yield.

Biostimulants, on the other hand, mainly help plants respond to environmental conditions and use available resources more efficiently, rather than serving as a primary nutrient source.

“Fertilizer feeds the plant, while biostimulants support the plant’s internal processes” — but neither can replace proper field management.

When Should You Consider Using Them?

Before choosing to use a biostimulant, first identify the actual cause of the problem. If a plant shows signs of nutrient deficiency — such as N, P, K, or micronutrients — or has issues related to roots, soil, water, pH, salinity, disease, or pests, using a biostimulant alone usually won’t resolve the underlying cause.

The right approach is: “fix the root cause of the problem first, then use a biostimulant to support the plant’s potential.”

Use should have a clear goal — for example, supporting root development, helping the plant through stress, promoting flowering and fruit set, or supporting yield quality — and then the type of product and timing should be chosen to match that goal. If a plant clearly lacks N-P-K, or has problems with waterlogging, drought, or improper pH, these core issues should be addressed first, since a stimulant alone cannot fix an underlying cause.

So when considering whether a plant stimulant is necessary, look at the plant’s actual condition and needs — it isn’t required in every situation. Once the main factors have been addressed, a stimulant can then be considered based on its intended purpose, such as supporting recovery or root development.

Guidelines for Choosing Fertilizer and Developing Products Suited to Plants

Information to Use Before Choosing a Formula

Choosing a fertilizer formula should start with the plant’s needs and the intended purpose — not the formula numbers alone.

Factors to consider:

• Plant species and goal — e.g., boosting leaf growth, strengthening roots, promoting flowering, or developing fruit
• The plant’s growth stage
• Application method — broadcasting, fertigation, or foliar spray
• Soil and water test results
• pH and salinity levels
• Field environmental conditions
• Product form — granular, powder, or liquid fertilizer
• Ease of transport and storage

Considering these factors together leads to a formula better suited to real-world use, rather than simply choosing the formula with the highest nutrient numbers.

For Those Looking to Build a Fertilizer Brand

Developing a fertilizer brand should start by identifying the target customer group and the problem to be solved — for example, which plant species the formula is for, when it will be used, and what unique selling point it should offer. From there, define the formula’s objective, select raw materials, determine concentration, and choose a product form that matches customer usage behavior.

It’s also important to verify product stability, packaging, usage instructions, labeling, registration, and accurate marketing claims. Working with a contract fertilizer manufacturer that can advise on formulation, raw materials, testing, and packaging helps keep the product development process clear and reduces errors before full-scale production.

Frequently Asked Questions

How do primary nutrients, secondary nutrients, and micronutrients differ? 

The main difference is the quantity plants need. Primary nutrients (N-P-K) are used in large amounts. Secondary nutrients (Ca-Mg-S) are needed in smaller amounts. Micronutrients such as Fe, Zn, and B are needed only in trace amounts.

If primary nutrients have already been applied, is it still necessary to add secondary nutrients or micronutrients?

 It depends on the plant species, soil and water conditions, and the existing nutrient levels. If the soil already has sufficient secondary nutrients or micronutrients, it isn’t necessary to add every type.

Does yellowing of leaves always mean nitrogen deficiency? 

Not always. Yellowing leaves can result from a deficiency in nitrogen, magnesium, iron, or other elements, as well as from root problems, plant disease, over- or under-watering, and improper pH.

Summary: What Nutrients Do Plants Need?

Key Principles for Application

Understanding what nutrients plants need shows that plants rely on primary nutrients, secondary nutrients, and micronutrients — each group playing an important, distinct role in growth. Plant care should therefore focus on nutrient balance rather than simply increasing fertilizer quantity.

Choosing a fertilizer should take into account plant species, growth stage, soil, water, root system, and pH together, so that the nutrients applied can actually be used effectively.

Starting Systematic Product Development

For those looking to start a fertilizer business, begin by clearly defining the target customer group and the problem to be solved. From there, develop the formula, select raw materials, choose the product form, and design packaging that aligns with real-world use.

There’s no need to pack in the maximum amount of nutrients — the goal is to choose well-reasoned components that meet the target plant’s needs. If you want to produce fertilizer or plant supplements under your own brand, you can bring information about your target customers, target plants, and product concept to a contract manufacturer to evaluate the formula, usage method, and feasibility before starting full-scale production.