What makes a fertilizer biological?

All biological fertilizers are organic. But not all organic fertilizers contain active soil microorganisms making them biological.

Organic fertilizers have a goal.

Their goal is to make the soil biological. Think of most organic fertilizers as the starting point to transform your soil into a rich organic loam. So it's good to start with organic but boost the soils microorganisms like benneficial bacteria, mycorrhizae fungi and trichoderma.

Organic Fertilizer Types

1Humic Acids
These are bio-stimulants that are minerals mined from the Earth or sometimes plant based. Little to biology

2Animal By-products
Chicken feathers and bones, fish heads and guts, and bovine blood are animal fertilizers but due to the manufacturing process they aren’t very concentrated in soil microbes.

3Animal Manure
This is usually from human (Milorganite), chicken, cow, bat, or shore birds. depending if the product is composted before sale like chicken manure, then biology in the product is moderate to good.

Like the animal compost, plant and kitchen scrap compost can be an extremelyconcentrated source of biology. However they are not the symbiotic microorganisms that promote root growth.

5Biological Soil Amendments
Concentrated, commercial sources of mycorhhizae, trichoderma, and rhizobacteria are the biggest inputs of biology you can add to boost plant and root growth.


Organic fertilizers, Bio-stimulants, and Biologicals in that order.


Humic Acids

Animal By-products

Animal Manure


Biological Soil Amendments

So let’s look at some situations you might run into.

Great article on Soil organisms here!

New construction/new landscaping – These are usually very damaged soils. Construction earth moving and compaction have greatly degraded the natural soil biology.

Compost or manure

Humic acids

Biological soil amendments

Planting in existing soils – Soils that have been in production for some time have built up some natural soil biology. However a boost of biology in the planting hole is a great idea.

Manure based fertilizers

Biological soil amendments

Plants in decline – Top dressing with added biology and additional ingredients to help boost plant health.

Humic acids

Manure based fertilizers

Biological soil amendments

Sodding – Sod from the sod farm is very low in biology. They have applied copious amounts of fungicides and herbicides which has an adverse effect on soil biology.


Biological soil amendments


It’s a step by step process. Soils in nature, when damaged by fire, mud slide, or flood, follow a transition during the re-growing process. Airborne weed seeds and animal feet bring in hardy plants that can grow in damaged soils. These are called pioneer species. They start to die and decompose to add organic matter to the soil. Gradually these pioneer plants introduce biology which in turn allows later generations of grasses, shrubs, and trees to grow. By knowing what types of organic and biological fertilizers to use, and at what time, you can copy nature somewhat and speed up the establishment process of your next project. 


The Rhizosphere – Roots, Soil and Everything In Between

By: David H. McNear Jr. (Assistant Professor of Rhizosphere Science) © 2013 Nature Education 
Citation: McNear Jr., D. H. (2013) The Rhizosphere – Roots, Soil and Everything In Between. Nature Education Knowledge 4(3):1
All biological fertilizers are organic. But not all organic fertilizers are biological.