Why Do Plants Need Fertilizer and Manure?

Plants receive the nutrients from the soil, but most of the major nutrients plants need are depleted quickly, leaving plants unhealthy and weak. Fertilizers and pesticides are both necessary for plant health, but fertilizers are particularly important for plant growth.

Plants need fertilizer and manure to supply the nutrients they need to grow and be healthy. Fertilizer and manure add nutrients to the soil and improve soil quality. This helps plants grow taller and healthier, resist pests and diseases, and produce larger yields. 

In this article, I’ll explore fertilizer and manure and how they benefit plants. I will also explain the importance of soil fertility to plant growth and overall health and how fertilizer and manure contribute to it, so read on!

Overview of Fertilizer and Manure

Soil is the medium in which plants grow and contains the most nutrients that plants need. Potting soil is a similar medium but doesn’t necessarily contain the components of soil and may not have any nutrients. 

Regardless, both these soils need nutritional supplementation. Fertilizers and manure are soil amendments used to supply plants with nutrients and improve soil quality


Fertilizers are not growing mediums like potting soil. They contain the macro, secondary, and micronutrients that plants need to live and grow.

The macronutrients required by plants include the following:

  • Nitrogen
  • Phosphorus
  • Potassium

These nutrients are labeled as NPK on packets of fertilizer. 

The macronutrients are the most important nutrients for plant growth, which is why they’re labeled on the packages. While secondary nutrients and micronutrients are important, they’re needed in smaller quantities, so most plants can derive them from the soil. 

Macronutrients are needed in large quantities by plants. They’re used for foliage growth, root and stem development, water uptake, and flower and fruit yields. Ornamental and fruiting plants need a lot of fertilizer to support their yields, especially in the growing season. 

Plants use up macronutrients fairly quickly in the growing season, and the soil is depleted quickly. Whether your plants are rooted in the garden or in potting soil, they still need nutrient supplements throughout the growing season. 


Manure refers to animal waste and is a byproduct of agriculture. There are many different kinds of manure, and they are all rich in nitrogen and other elements. This is why they are used to organically supply nutrients to plants. 

Not only is manure a good fertilizer, but it is also a great soil amendment because it helps improve overall soil quality, which refers to the texture of the soil, how easy it is to work with, its water and nutrient retention capacities, and the aeration of the soil. Manure helps improve soil quality because it contains large amounts of organic matter. 

Composition and Nutrient Content

Fertilizer plays an important role in ensuring overall plant health and supporting yields. Using fertilizers and manure can reduce the cost of plant upkeep over time, though the cost of fertilizers can be high as well. Fertilizers, in particular, have been particularly effective in improving the profitability of farming worldwide. 

Fertilizers and manure contain a number of components for plants like:

  • Plant nutrients
  • Organic matter
  • Soil conditioners
  • Microbes
  • Pesticides
  • Water

Fertilizers and manure are made up of several components that are beneficial to plants.

I’ll explain what they do below so you understand why they’re important to plants:

Plant Nutrients

As we’ve discussed earlier, plant nutrients refer to the macro, secondary, and micronutrients that plants need to grow. Plants use the macronutrients in large quantities. However, they still need secondary and micronutrients for healthy root development and growth. 

Organic Matter

Organic matter is a naturally occurring group of nutrients present in fertilizers like compost and manure, improving soil quality. Soil is the medium in which plants grow, so it’s important that the soil is of good quality to ensure plant health and growth. 

Soil conditioners

Soil conditioners are sometimes added as inactive ingredients to inorganic fertilizers. A good example is gypsum waste, which is added to fertilizers to improve the texture of the soil and its capacity to retain nutrients like phosphorus. These soil conditioners can improve the plant’s ability to absorb essential nutrients.


Microbes are present in organic fertilizers like compost and manure, and they process the organic matter down, releasing nutrients and improving aeration. Some inorganic fertilizers like plant food spikes also introduce helpful microbes to the soil. 


A lot of inorganic fertilizers have pesticides like weed-killers mixed in. Other fertilizers like compost tea can be used as an alternative to fungicides and provide nutrients to plants, especially when applied to the leaves. 


Liquid fertilizers are suspended in water and then added to the soil. The additional water supports nutrient intake and prevents cases of fertilizer burn. Plants take a long time to recover from fertilizer burn, so water is an important component to dilute the fertilizer with harsh components.

Categorization of Fertilizers

As we’ve discussed, fertilizer is added to soil to add nutrients that plants need to grow and develop well.

Fertilizers can be categorized in different ways:

Process of Making It

Based on whether organic or synthetic processes make the fertilizer, fertilizer can be organic like compost or manure, or inorganic. 

Nutritional Ratio

Fertilizers can be nitrogen-heavy like manure or ammonia sulfate or phosphorus heavy like bone meal. They are often categorized based on the nutrient found in the fertilizer’s largest proportion.

How the Nutrients Are Released

Most inorganic fertilizers are designed to be water-soluble, so the nutrients are immediately available for plant use. However, organic fertilizers and plant food spikes are designed to be slow-release.

Physical State

Fertilizers may be solid like granules, plant food spikes, manure, and compost. Or they may be liquid, like in the case of compost tea and other water-soluble synthetic fertilizers. Solid fertilizers can be made into liquid if necessary.

Using Manure as a Fertilizer

Manure is an important fertilizer used on farms and is a great fertilizer for houseplants, regardless of whether they’re indoor or outdoor plants. Manure is rich in the plant macronutrients like nitrogen, phosphorus, and potassium. 

Besides NPK, manure is a good source of secondary and micronutrients like calcium, magnesium, and sulfur. All of these nutrients are important for plant growth and healthy development.

Most manures are a good source of nitrogen, and chicken manure is often used to add nitrogen to a dry and nitrogen-deficient compost. 

The Risks of Using Fresh Manure

Fresh manure is often not recommended for plants as the nitrogen content is high and might damage the plants. Overfertilization is just as bad as under-fertilization, leading to deformed growth and even plant death. Fresh manure is also dangerous because of the bacteria and other pathogens present, which can cause diseases if improperly handled. 

Manure is an organic fertilizer, which means that the processes of manure production are entirely organic. Due to this, the proportions of nutrients vary in each batch of manure. Additionally, the NPK ratios are rarely balanced.

The Benefits of Using Manure

Nevertheless, manure adds organic matter to the soil as well. It improves the texture by breaking up the soil particles and inviting microbial activity. The organic matter helps the soil retain water and nutrients, which reduces the need for fertilizer application. 

Manure can be applied directly onto the surface of the plants or worked into the soil to avoid the toxic smell. Manure may be solid or diluted with water to make a liquid fertilizer. Liquid manure has a lower nutrient concentration but works faster than solid fertilizer. 

Manure can be used in combination with more traditional synthetic fertilizers to improve yields, plant health, and soil quality. 

In the long run, organic fertilizers like manure are better for your plants than synthetic fertilizers. Using the two in tandem helps maintain soil quality while supplementing plants with the nutrients they need. Consistent applications of manure will ensure fertile soil that will not need as many applications of fertilizer. 

Fertilizer or Manure: How to Choose

The type of fertilizer you choose will depend on several factors, including: 

  • The type of soil you’re using
  • The nutritional levels of the soil
  • The soil pH value
  • Its texture

Let’s check them out in more detail below:

The Type of Soil

If your soil compacts easily because of a higher ratio of clay particles, you might want to use an organic fertilizer. Compost and manure tend to add organic matter and improve overall soil quality and nutrition. 

Manure tends to increase the aeration quality of clay soil or the moisture retention capacity of sandy soil.

Availability of Nutrients in the Soil

Most plants do well with a balanced fertilizer with equal proportions of nitrogen, phosphorus, and potassium. However, seedlings need fertilizers that help with root growth, so you might need to give your seedlings some phosphorus-rich starter fertilizer.

Some gardeners conduct a soil test like to determine the kind of fertilizer to use based on the availability or lack of nutrients in the soil.

It’s customary for commercial fertilizers to indicate the amount or proportion of nutrients within a pack of fertilizers. The packaging also indicates how to use or prepare the fertilizer formula. That is why it’s best to use synthetic fertilizers with known nutritional levels.

Speed of Nutrient Release

Fast-release fertilizers are important for plants that need immediate access to nutrients, like crops, ornamental plants, and fruit trees. On the other hand, slow-release fertilizers are a great option for feeding outdoor shrubs and trees.

These fertilizers, like plant food spikes, only release as many nutrients as a plant needs, so there’s no risk of overfertilization

Plants easily take up liquid fertilizers as nutrients need to be suspended or carried in water before plants can absorb them. With solid fertilizers, the particles are broken down till they’re small enough to be suspended in the water in the soil or till they dissolve. Then the nutrients can be absorbed by the plants. 

So you would apply liquid fertilizers if your plants need the nutrients urgently, especially because liquid fertilizers can also be sprayed on the leaves.

Pros and Cons of Nutrient Supplementation


As we’ve seen, several elements in fertilizer and manure are particularly beneficial for plants. While fertilizer isn’t strictly necessary, it does offer plants several advantages.

Here, I’ll list the main advantages of using fertilizer and manure for plants:

Improved Plant Growth

Plants supplemented with fertilizer and manure tend to grow faster and taller and have denser foliage than plants grown without fertilizer. The nutrients from fertilizer and manure offer more resources for plants to grow. 

Better-Developed Root Systems

Plants of all kinds develop extensive root systems if given the opportunity. Roots ensure plant stability, hydration, and nutrition. Plants with access to enough phosphorus can grow deep and healthy roots. This allows them to grow stronger and absorb nutrients from deeper soil layers. 

Pest and Disease Resistance

Fertilizers help plants become healthier, which allows them to build up their natural defenses. A healthy plant is better placed to recover from a disease or an attack by pests or even ward them off entirely. Over time, the use of fertilizers reduces the dependence on pesticides and fungicides. 

Larger Yields

The primary advantage of fertilizers is larger yields. As plants have more nutrients available, they can use the resources to produce more flowers and fruits. Fertilizers also help plants grow faster, which ensures a longer flowering and fruiting season. 


While fertilizers and manure can benefit plants and gardens in many ways, they also have their own challenges.

Here are some of the common disadvantages of using fertilizer and manure:

Excess Nutrition

Too much fertilizer is bad for plants as well. If you add fertilizer and manure to your garden indiscriminately without checking your plant’s requirements, then you’ll end up overfeeding your plants. This could lead to wilting, deformed growth, excess foliage, and a reduced yield. 

Fertilizer Burn

Fertilizers are made up of mineral salts, which supply nutrients to the plants. A build-up of these mineral salts in the soil will draw water out of the plant tissues, causing fertilizer burn. Symptoms include leaf and root scorch, yellowing of leaves, wilting, and plant death. 

Wastage of Fertilizer and Nutrients

Often, fertilizers and manure are applied incorrectly, which leads to wastage. Adding too much fertilizer, excessive watering after fertilizing your plants, and adding nutrients your plants don’t need all lead to nutrient loss. 

Runoff Leading to Pollution

Excess or unused fertilizers accumulate in the soil. These may disperse through the soil and enter groundwater or get washed away into nearby water bodies. Fertilizers pollute the water bodies by causing excess algae growth, which crowds the surface and sucks up all the oxygen in the soil. 

Excess Acidification

Soil pH values are important as they determine the nutrients available to the plants. However, prolonged use of fertilizers can lower the pH values below the ideal levels, leading to highly acidic soil that doesn’t sustain life. 

The Relationship Between Soil Fertility and Plant Health

Soil fertility refers to the density of plant nutrients in the soil that allows it to sustain the life and growth of your plants. 

Apart from the presence of nutrients, soil fertility also depends on the capacity of soil to make these nutrients available to plants. This is dependent on the composition of the soil, its pH values, water retention capacity, and nutrient retention capacity. 

Soil can be categorized as clayey, sandy, or loamy. As the name suggests, clayey soil has a higher percentage of clay, and sandy soils have a higher percentage of sand. 

Clay-based soils tend to have higher retention capacities, but the compaction of the soil makes it difficult for plant roots to absorb nutrients. They also have poor drainage. In contrast, sand-based soils tend to have very good drainage, and as a result, a lot of nutrients and water are easily drained away. 

Loamy soils have a balance of clay, sand, and silt that allows for great drainage, so the plant roots aren’t swimming in water. The silt and clay retain nutrients and water as well, which makes it easy for plants to access and uptake nutrients. 

The pH values of loamy soils tend to be more or less neutral, which ensures that the nutrients in the soil are made available to plants for uptake.

Fertile soils are able to sustain more plant life, and plants that grow in fertile soils are able to grow taller, faster, and stronger because they have access to more nutrients. Soil fertility is essential to ensure greater yields and healthier plants. 

The Effects of Amendments on Soil Fertility

Fertilizers and manure contribute to soil fertility quite literally by adding nutrients to the soil. They are the majority source of the soil’s acquired fertility (as opposed to its inherent fertility). 

They also amend the soil’s pH value by making it more acidic. Mildly acidic soils are actually necessary for the fast release of nutrients, especially from organic matter like bone meal. Manure and compost are great organic fertilizers that lower the pH value of the soil and make it more fertile. 

When used correctly, manure and other fertilizers, especially organic fertilizers, improve the overall nutrition, pH values, and moisture content of the soil. The application of organic fertilizers improves the soil’s inherent fertility over time. 

Final Thoughts

Plants need fertilizer and manure not only for the nutrients they provide but also to improve the quality of the soil. Better soil quality ensures plants that need fewer applications of fertilizer have developed strong roots and resistance to pests and disease. 

Plants that can access more nutrients are also able to produce bigger yields more quickly over a longer period. 

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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