told to mix “browns” and “greens” together for a good balance of carbon from
the “browns” and nitrogen from the “greens”. I am puzzled. All living things
have both until they are composted. To me, the browns add fluffy aeration to
the soil while the greens clump together in the compost pile. Is it possible
that the mix of browns and greens is as much for texture as it is for carbons
and nitrogen?
that requires a lot more space than this column permits. Compost is used as an
amendment for soils for two reasons; because it can positively change the chemistry
and structure of soil. I will try to answer it more completely in my blog.
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| Composts applied to soilsboth chemically and physically alter it.Most compost have an acid reaction and lower the soil pH. It adds nutrients to the soil. The type of nutrients it adds depends on what was used to make it. A wide variety of “brown” and “green” will give it a wide variety of nutrients. Composting with wood products that have been industrialized with chemicals such as fire retardants, paints, preservatives will end up in the compost made. Garbage in, garbage out. |
Browns and Greens
The terms “browns” and ‘greens” are a simplification for the
average person to make it easier to choose the correct plant ingredients when
making compost. Dry wood, or sawdust made from wood is about 50% carbon by
weight. The amount of nitrogen in sawdust is about 400 – 500 times less than the carbon. So, the carbon to
nitrogen ratio of sawdust is about 400 – 500 carbons for every single nitrogen
(brown).
nitrogen or less. Extra nitrogen must be added to this sawdust from “green”. It just so
happens that food waste (greens) has about 20 carbons for each nitrogen. This
is about the same as coffee grounds, which happens to be “brown”. The “brown
and green” rule doesn’t always work!
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| Some composts are very rich (less than 20 carbons to one nitrogen) while others are not. Those very rich composts can also be used as a source of fertilizer for plants. They can’t be marked as a fertilizer because the fertilizer content is not the same with every batch of compost. There are fertilizer laws in every state in the US. To be called a fertilizer, the amount of nutrients in each sack or volume must be consistent.This is the reason composts cannot be called fertilizers. |
Using Fertilizers As a Greens Substitute
Another option is to add nitrogen to the carbon or “browns” with nitrogen fertilizer such as 21-0-0 or 46-0-0. A much smaller volume of fertilizer is needed than “greens”. This may not sit very well with some people such as the “organic crowd”. The plant doesn’t care where the nitrogen comes from but there are potential contaminants in mineral fertilizer products. Ornamental trees and shrubs that constitute “green waste” may be sprayed with pesticides. Sometimes it is impossible to know.
Animal Manure
Many composts use farm animal manure, rich in nitrogen,
in combination with wood or paper products rich in carbon. Farm animal manures
can be as low as 12 carbons for each nitrogen. Human manure can be as low as 6
carbons for each nitrogen. On top of that, animal manures are easier to collect
and transport for composting.
right proportion, voilà. The compost
has the magical carbon to nitrogen ratio less than 40:1. I usually aim for a
carbon to nitrogen ratio close to 20:1.
Best to Carbon to Nitrogen Ratio
40 (C:N = 40) has a small amount of nitrogen to give to plants. Compost with
C:N = 20 has much more nitrogen to provide and can act similar to a fertilizer
when applied to the soil near plants. But carbon and nitrogen aren’t the only “fertilizers”
supplied by compost. The composting process releases all the nutrients
contained in the ingredients. What goes in, must come out.
structure of a soil. It acts very similar to peat moss and coir, making it more
“fluffy”, while providing many more nutrients to the plants.
I recommend the following:
guideline about how much nitrogen to add to a compost
have a range of nutrients locked inside them
adding feedstocks loaded with contaminants.
• I don’t agree about not composting animal carcasses or animal by-products. It can be done. On farm composting of dead
animals is a common practice. But it must be done correctly.