Organic or mineral fertilizer? Which is better for soil, trees, and other plants?

Table of Contents

• The key difference: How do the fertilizers work?
• Plant nutrition or soil health?
• Why healthy soils are more important today than in the past
• The advantages of organic fertilizers
• Why mineral fertilizers are not always the best solution
• Why healthy soils can retain water better
• Worm compost as organic fertilizer and soil improver
• Organic or mineral – which is better?

Plants need nutrients to grow. Anyone wanting to fertilize their garden, flowerbeds, or trees will therefore sooner or later face an important question: Should I use organic or mineral fertilizer?

Both types of fertilizer supply plants with essential nutrients. However, they differ fundamentally in their mode of action. While mineral fertilizers usually make nutrients quickly and directly available, the nutrients in organic fertilizers are predominantly released only through biological processes in the soil.

This article explains the differences between organic and mineral fertilizers and the advantages and disadvantages of each. Here's a basic article on the topic. Fertilizing trees. 

Key facts at a glance

• Mineral fertilizers usually provide nutrients quickly and in a targeted manner.
• Organic fertilizers usually release their nutrients more slowly.
• Organic fertilizers can introduce additional organic matter into the soil.
• Compost and worm compost can support soil life and humus formation.
• Soils rich in humus are better able to retain water.
• Which fertilizer is appropriate depends on the plant, soil, and nutrient requirements.

The key difference: How do the fertilizers work?

The most important difference lies not primarily in the nutrients themselves, but in how these are made available to the plants.

mineral fertilizer

Mineral fertilizers contain nutrients in dissolved or readily soluble form. These include, for example, nitrogen, phosphorus, and potassium. Well-known products are blue granules or other NPK fertilizers.

After application, the nutrients dissolve in the soil water and are immediately available to the plants. The effect is usually rapid. Often, noticeable growth reactions are visible after just a few days.

Organic Fertilizer

Organic fertilizers consist of natural materials such as compost, worm compost, manure, horn shavings or plant residues.

The nutrients contained in the fertilizer must first be broken down by soil organisms. Bacteria, fungi, earthworms, and other soil creatures perform this task. Only then can the plants absorb the nutrients. Therefore, the effect is slower to take hold, but usually lasts significantly longer. 

Plant nutrition or soil health?

Both types of fertilizer supply plants with nutrients. The difference lies in their focus.

Mineral fertilizers are primarily used to supply plants with specific nutrients quickly and efficiently. Organic fertilizers also provide nutrients, but depending on the source material, they additionally introduce organic matter into the soil. Compost and vermicompost, in particular, can thus also support soil structure, soil life, and humus formation. This difference plays a crucial role in maintaining sustainable soil fertility.

Why healthy soils are more important today than in the past

Longer periods of drought, more frequent heat waves, and heavy rainfall events pose major challenges for trees and other plants. At the same time, many soils are compacted, low in humus or burdened by intensive use. Healthy soil acts as a buffer against these stresses.

Healthy soil stores water, provides plants with nutrients, and offers a habitat for billions of microorganisms. The better the soil quality, the more resistant plants are to drought stress and other environmental stresses.

The advantages of organic fertilizers

1. Long-term soil improvement

Organic fertilizers can contribute to soil improvement in addition to providing nutrients. However, the extent of this effect depends on the starting material. Compost, worm castings, and other organic materials, for example, introduce organic matter into the soil.

The organic matter is gradually incorporated into the soil. This creates stable soil aggregates that can better absorb air, water, and roots. Loose soils promote healthy root growth and reduce the risk of waterlogging or compaction.

2. Promoting soil life

Beneath our feet lives a fascinating world of microorganisms, fungi, earthworms, and other soil organisms. These organisms decompose organic material, make nutrients available, and contribute to the formation of fertile soils.

Organic materials can serve as a food source for many soil organisms, thereby supporting biological activity in the soil. Active soil life is the foundation for healthy plants in the long term.

3. Humus build-up

Humus is one of the most valuable components of soil. It improves soil structure, stores nutrients, and serves as a habitat for numerous microorganisms. 
Organic materials and organic fertilizers such as compost and worm castings provide the basis for humus formation. Each application builds up and improves the soil in the long term.

Mineral fertilizers cannot accomplish this process because they contain no organic matter.

4. Improved water retention

Soil rich in humus can store significantly more water than soil poor in humus. This is particularly important in times of increasing drought. 
Humus acts like a sponge. It absorbs water and gradually releases it back to the plant roots. This keeps plants supplied with water for longer and reduces their susceptibility to drought stress. This is particularly important for trees, which often grow in the same location for many years.

Why mineral fertilizers are not always the best solution

Mineral fertilizers certainly have their place. They deliver nutrients quickly and precisely, and are therefore also used in professional horticulture.

However, frequent or improper use can lead to disadvantages. These include:

• Leaching of nutrients into groundwater
  
• increased risk of over-fertilization
  
• potential contamination of soil organisms
• no contribution to humus formation
  
• no improvement in soil structure

Their advantages, on the other hand, are:

• Nutrient amounts can be precisely dosed.
• Nutrient deficiencies can be quickly corrected if diagnosed correctly.

Why healthy soils can retain water better

An often overlooked advantage of organic fertilizers lies in their effect on the soil's water balance. Soils with a high humus content can store significantly more water than depleted or compacted soils. At the same time, they improve rainwater infiltration and promote deeper root penetration. This means:

• less surface runoff
• improved water retention
• reduced drought stress
• more robust plants

Fertilization and irrigation are therefore closely linked. Healthy soil uses available water much more efficiently. You can find more information in the article. Properly caring for trees: the interplay of water, soil and nutrients.

Worm compost as organic fertilizer and soil improver

Among organic fertilizers, Worm compost Worm compost occupies a special position. During digestion by composting worms, organic materials are biologically enhanced. The result is a fertilizer with high biological activity. Worm compost provides:

• plant-available nutrients
• valuable microorganisms
  
• Support for soil life

Worm compost can be used particularly effectively for trees, raised beds, vegetable beds or potted plants.

Organic or mineral – which is better?

There is no single answer. The decisive factors are the existing soil, the plant, and its actual nutrient requirements. Mineral fertilizers can be useful if a specific nutrient deficiency needs to be corrected quickly and effectively.

Organic fertilizers and materials such as compost or worm castings are particularly suitable when, in addition to nutrient supply, organic matter and soil life are also to be promoted. Especially with trees, fertilization should not be done preventively, but only when there is actually a need.