What is compost? Why is it beneficial for plants? And why is it when you only use compost in your growing media it will not allow for good growth in plant?

Compost is the term we use to describe the end product of control decomposition of organic mater. When you build a composting pile, you are hoping to create the environmental conditions necessary to speed up decomposition with bacterial and fungal actions. There are many ways to facilitate this action that range from mixing, saturation, oxygen infiltration, and mass accumulation. The primary breakdown of all organic mater first starts with the bacterial decomposition as the plant mass you accumulate has high amounts of nitrogen {for protein synthesis} and high moisture {for single cell organisms}. As the bacteria colonies consume and grow in the mass, they also consume oxygen and water, while expelling secondary waste products that can be consumed by other bacteria to use in their own metabolism. This processes generates a large amount of heat, which also helps to speed up bacterial decomposition, but also can generate a dry anaerobic environment if left unchecked. As the bacterial colonies start to mature, and the pile is left alone {unturned} while in the presence of adequate oxygen, fungal spores will start to germinate and spread across the organic material. these fungal networks serve 2 major purposes for the pile: transporting water throughout the pile, and connecting debris so bacteria can easily travel between particles and consume more material. Once the pile has fully matured, you should expect to have a ratio 4 bacteria:2 fungi:1 organic node. Now depending on how you manipulate your pile you can have greater density of bacteria, or fungi, but this would be the ideal ratio under a microscope.

So why is this beneficial for plants? well this allows for a hyper concentrated form of primary and secondary soil biologics that are needed at the root zone of plants for immunity and nutritional functions. As the plants send down their secondary metabolites {root exudates} they form communities and a shared ecosystem with these bacteria and fungi helping them grow based on the requirements of the plant itself.

Given this relationship, why is pure compost or half finished compost not an ideal substrate for plants to grow? This is because the nutrients are actually locked up in the living biomass of the bacteria and fungi, with their waste products being used by other bacteria and fungi to grow and reproduce. This effectively turns the original compost material into inaccessible forms for the plants to take up as they do not have the capacity to trap and digest the organisms themselves.

So how do plants access these nutrients? By enlisting the aid of primary and secondary predators such as nematodes and microarthropods that consume these organisms and secrete inorganic waste products. It is the inorganic waste from these worms and insects that the plant actually absorbs and utilizes, not the waste from the bacteria themselves.

So to rebuild soil structure and create the adequate environment to grow plants, you do want to compost your organic materials, but you will also want to take samples from healthy soils in order to get the soil invertebrates needed to break down the decomposers so your plants can function.

As an anecdote from myself. our engineered soils for above ground containers use a mix that is 10% finished organics, 20% stable organics {charcoal dust}, 60% rock fines, 10% clay powder.

If you are doing inground plantings, you can amend your soils by adding finished compost that has charcoal and rock dust added in before the composting starts, or you can do any number of soil amending techniques that have been proven from all over the world and in laboratory settings. Remember that the soil is your bank of nutrients and biologics, and everything you take out should be given back in one form or another otherwise you will kill your land and make it unproductive.

The rate of compost is based on the available food, the size of the composting material, how much air you have in the mix, and how moist it is.

The way to tell if your mix is active is that it will start generating its own heat, building up to 160F for hot compost.

Unlike those commercial, expensive, automated composting machines it will take a minimum of 6 weeks of turning and adding until you start getting finished compost. Do not worry about perfect ratios, just add material. You want it to be more dry than soaking wet, because you can always add moisture.

Thanks to BiotechFarmer for his contribution to this section.