COMPOSTING & PLANT NUTRITION
Rodale emphasized that the best way to feed the garden was to feed the
soil organisms. The soil organisms have a central role in converting
materials into plant nutrients, making these nutrients available to the
plants, and the overall nutritional process. Feeding the soil organisms
means making sure that they have an adequate supply of air, water,
organic material, and the various essential mineral nutrients. The
process by which soil organisms convert materials into plant nutrients
is similar to the process that takes place within the compost pile or
bin. This session is about plant nutrition, composting, and the ways
compost can be used in the garden.
Mother Nature says that once you are finished using something, you
should put it back. Composting is the way Mother Nature processes this
returned material. The process is mostly biological. Composting is the
collective feeding and digesting of materials by the community of the
living organisms. Maintaining a compost pile or bin speeds up the
USES OF COMPOST:
Compost is a valuable material that does many jobs and does them well.
There always seem to be the need for more compost than is available.
The uses include:
- NUTRIENT SOURCE FOR THE SOIL ORGANISMS: Compost is the best,
all around source of organic material as a nutrient for soil
organisms. The composting process has "pre- digested" a lot of the
material making it easier for the soil organisms to assimilate as
nutrients. Composted material is also cleaner relative to
pathogens, salts and other toxic materials.
Most garden soils are low in organic content. Making the soil
richer in organic content, increasing the quantity, diversity and
activity of the soil organisms. One of the activities of the soil
organisms is the consumption of this organic matter. The feeding
of the soil organisms needs to be on-going. Generally speaking,
the soil organisms in regions with a relatively short growing
season can consume a 2" ( 5 cm) layer of compost or composted
manure per year. In regions in which the growing season is
extended or continuous, they can consume twice that much. It takes
a lot of organic material to feed the soil organisms.
- NUTRIENT SOURCE FOR THE PLANTS: It is often said that compost
is a soil amendment and not a fertilizer. This is mostly an issue
of semantics. The manufacture and sale of synthetic fertilizers is
big business. Trade associations prevailed on a number of State
governments to pass legislation that prohibits the sale of manures
and composts as "fertilizers". The justification was that manures
and composts are generally low in their content of mineral
nutrients and particularly in terms of the trace elements. The NPK
numbers for a typical compost would be somewhere around
In practice, NPK numbers are only half the story. Plant nutrition
involves the processing of minerals and other nutrients by the
soil organisms. Feeding the garden means feeding the soil
organisms and compost is an excellent source of these nutrients.
At the use level, compost contains adequate levels of the various
mineral nutrients but can be shy of trace elements. Fish emulsion
or fish meal usually contain enough of the trace elements that
supplemental feedings with either material would correct possible
- SOIL AMENDMENT TO IMPROVE STRUCTURE: Compost is the organic
material of choice to improve soil structure. It helps the soil
particles to bond and form soil aggregates; it helps in the way
these aggregates retain and release plant nutrients; and it helps
to create better porosity. Compost, better than any other
material, helps clay soil to become workable.
- SOIL AMENDMENT TO IMPROVE DRAINAGE: Organic material, in
general, will amend slow draining clay soils to drain faster and
sharp draining sand soils to drain slower. Compost is of
particular value as a soil amendment to improve drainage in that
it works so well and is so easy to use.
- MULCH TO MINIMIZE PROBLEMS WITH WEEDS: A good 2" (5cm) layer
of compost works very well as a mulch but with the understanding
that this mulch layer is temporary. The compost layer is
eventually consumed by the soil organisms, particularly by
earthworms, adding to the life of the soil.
The mulch layer serves as a physical barrier keeping weed seeds
from getting into the soil and as a light barrier keeping weed
seeds that are already in the soil from germinating.
- MULCH TO MINIMIZE LOSS OF SOIL MOISTURE: Compost acts like a
sponge and retains moisture. A layer of compost on the soil
surface will catch and hold moisture that would otherwise
evaporate from the soil. This helps to minimize the loss of soil
moisture. The flip side is that it also tends to catch and hold
water that would otherwise enter to irrigate the soil. Too thick a
layer of compost as a mulch can create watering problems.
- MULCH TO INSULATE SOIL: Compost has good insulating
properties and a layer of compost slows down changes in soil
temperatures as a result of changes in the weather. Soil organisms
do better when temperature changes are gradual.
REASONS TO COMPOST:
It is difficult to make enough compost for the garden. The need
exceeds the supply and the temptation is to buy compost from
commercial sources. The packed commercial compost that one might buy
from reputable garden centers may be completely O.K. regarding
ingredients as well as being completely appropriate for the home
garden. A lot of the packaged material, however, contains composted
sewer sludge which often contains heavy metals that are soil toxic. A
lot of the bulk commercial compost is based on commercial or
industrial wastes. Again, these material may or may not contain
problem materials but there is no good way of knowing. There are no
real standards and the contents of commercial composts are not
Making your own compost from materials collected from your own garden is
the best way to regulate the contents. It makes no sense to discard
clippings from a clean garden that would make clean compost and to go
out and buy the commercial material that may or may not contain problem
materials. This is particularly true if the garden is used to grow foods
for the table.
Composting is also good citizenship. Anything that we can do to reduce
the quantity of material that goes into land fill is a good thing.
According to the Los Angeles County Department of Public Works, for
example, Los Angeles County disposes of 40,000 tons of waste per day.
That's enough to fill Dodger Stadium every 11 days!. 20% of that 40,000
tons is yard waste that could have been composted at home. A 20%
reduction in land fill operations would be of huge value to the
environment and it would also save huge sums in disposal costs.
The processes involved in the rotting or bio-degradation of materials
in nature is mostly biological. Primarily, it is living organisms
feeding on complex materials and then converting this materials into
simpler forms by digestion. Composting is the same cluster of
processes but with optimized conditions to speed things along.
Specifically, to optimize conditions for the living organisms which
- Protecting them from the elements;
- Protecting them from toxic materials and
- making sure that they get enough air, water and nutrients.
PROTECTION FROM THE ELEMENTS:
The composting process generates heat and, in turn, heat hastens the
composting process. Composting bins or piles work better when they are
protected from chilling winds. As the organisms also do best in moist
conditions, they should also be protected from drying winds or from
being flooded out.
PROTECTED FROM TOXIC MATERIALS:
The organisms responsible for composting, like all living organisms,
are vulnerable to the effects of toxic materials. Just because one can
compost almost any organic or mineral thing, it doesn't mean that the
organisms can't be injured or destroyed if toxic materials get into
the compost bin or pile.
Wood ash, for example, is a rich source for both Potassium and
Phosphate. It is also a very alkaline material. A little wood ash would
be a worthwhile addition to the composting material but one could add
too much and do considerable damage to the ecosystem of the compost pile
MAKING SURE THEY GET ENOUGH AIR, WATER AND NUTRIENTS:
The compost pile should be turned and mixed about once a week so that
the material on the top moves to the bottom and the material on the
inside moves to the outside. Turning and mixing the pile lets in the
needed oxygen. A compost pile should be kept about as damp as a
wrung-out sponge. Proper amounts of air and moisture are necessary for
the process to work efficiently.
The key to hot, fast compost is equal parts of "brown" and "green"
materials. The organisms that do the work of composting need carbon
based materials and nitrogen based materials for their personal diet and
for their finished work product. The "green" or high nitrogen materials
include: grass clippings, garden trimmings, green leaves, manures and
scraps from the kitchen. They are high nitrogen because they contain
appreciable amounts of protein and/or amino acids. The "brown" or high
carbon materials include: wood chips, sawdust, straw/hay, dried leaves,
and shredded paper. They are high carbon because they contain
appreciable amounts of cellulose.
Do not put meat, bones, milk or milk products, fat, or dog or cat
droppings into the composting pile.
MAKING COMPOST BINS OR PILES:
Ideally, a compost pile or bin should be in a sheltered part of the
garden, on level ground with reasonable drainage, and have enough room
around it to make it convenient to work. It should have a convenient
water source, with good air circulation on at least three sides, and
it ought to have one end that can be opened for adding and removing
material. It should be able to hold approximately a cubic yard or 3/4
cubic meters. In practice, make it as close to the ideal and
convenient as possible.
MAINTAINING COMPOST BINS OR PILES:
"The Rapid Composting Method" by R. Raabe lists the following:
- Woody material should be chopped to ½ to 1 ½ inch (2 - 4 cm) bits.
Soft succulent tissues need not be chopped.
- Carbon-to-Nitrogen ratio in a compost pile should be 30 to 1. A
mixture of equal parts of green plant material and dry plant material
(dry leaves, woody prunings, straw, shredded paper) will normally
achieve this. If the C/N ratio is less than 30 to 1, the compost will
give off an ammonia odor. Add sawdust to counteract this.
- Do not put soil, ashes from a stove or fireplace, or manure from
meat-eating animals in the compost.
- A compost pile should be at least 36"x36"x36" (1 meter x 1
meter x 1 meter) to assure adequate heating. Heat retention is
better in bins than in open piles. Pile temperature should
remain at 160 degrees F. (70 degrees C.) to kill pest
organisms. Get a thermometer to check the temperature. Do not
let temperatures get more than a few degrees higher;
decomposing micro-organisms will be killed. Frequent turning
will prevent overheating.
- Turn a pile every 1 to 2 days to keep it from getting too hot
and to aerate it. Piles turned every day should take about 2
weeks to compost; those turned every two days will take about 3
- Once the pile is started, do not add anything (unless your
compost is not functioning properly and you add sawdust, water
or nitrogen as described in numbers 2 or 7).
- If temperature do not get up to 160 degrees F (70 degrees C)
within 24 to 48 hours, the pile is too wet, too dry, or there
is not enough nitrogen (green material). If too wet, spread out
the pile to dry. If too dry, add water. If not enough nitrogen,
add a material high in nitrogen (grass clippings, fresh chicken
- A healthy compost will have a pleasant odor, give off heat when
turned, have a white fungal growth on the decomposing material,
will get smaller each day, and will gradually change color to
dark brown. When no further heat is produced, the compost is
ready to use.
Sheet composting is spreading a layer of extra organic material
directly on the bare ground or over a green manure crop. The material
is then tilled into the soil and the soil organisms are supposed to
take it from there. It is a quick way to add organic material to the
soil and it is also relatively easy. It is, however, a good way to
spread problems throughout the garden because the organic material
does not get hot enough to kill pathogens or weed seeds that might be
Green manuring is the growing of cover crops to be turned under the
soil surface. "The Rodale Guide to Composting" says that green
manuring "is the most practical way for the farmer to add substantial
amounts of organic matter to land areas. The green manure crop,
usually a legume, is most often planted after a food crop has been
harvested or as a nurse crop with it, and is turned under about six
weeks before the next crop is to be planted."
Sheet composting and green manuring both require that the organic
material to tilled or turned into the ground. This is often not
practical in the home garden.
Vermicomposting is composting done with earth worms. It is done in a
worm box with drainage holes in the bottom, air holes in the sides,
and a light tight cover or lid. The operation is clean, odorless and
tidy to the point that the bins are often kept in basements or even
inside the house. The purpose of vermicomposting is to generate and
collect worm castings which are used as a fertilizer mostly for potted
plants. Worm castings are rich in plant nutrients, odorless, and slow
Generally speaking, earthworms will eat their weight in kitchen
scraps and produce their weight in worm castings every day. Earth
worms like soft foods such as cooked vegetables, left over cereal,
left over vegetable soup, soft leaves of vegetables (especially
lettuce), bread scraps, and even ice cream. Castings are harvested
about every three months.
The worms best suited for vermicomposting are red manure worms,
Lumbricus rebellus and red wigglers, Eisenia foetida. The night
crawlers, Lumbricus terrestris, need cool soil temperatures and don't
survive in a worm box. One source for commercial red wigglers, worm
boxes and detailed instruction is Down to Earth-Worms in British
Columbia, @ 604-374-5718. The best reference is Mary Applehof's
"Worms Eat My Garbage".
"The Nature and Properties of Soils" by Brady makes the point that
garden soil is an ecosystem and that the things that go on in the
garden impact on the way things go on in the soil . . . and that the
way that things go on in the soil impact on the way things go on in
the garden. In essence, talking about plant nutrition in terms of
nutrient management rather than in terms of fertilizer. Brady then
lists what he considers as the four major goals of nutrient
Brady seems to repeat Rodale's central theme, "The best way to feed
the garden is to feed the soil organisms."
- Cost-effective production of high quality plants
- Efficient use and conservation of nutrient resources
- Maintenance or enhancement of soil quality
- Protection of the environment beyond the soil
The essential macro-nutrients are frequently divided into three major groups:
- NATURAL ESSENTIAL NUTRIENTS . . . those nutrients that are
supplied freely by nature in more than adequate amounts; they are
materials that are derived from air and water: Carbon, Hydrogen,
- PRIMARY ESSENTIAL NUTRIENTS. . . those essential nutrients
that are usually added by the grower and needed in the largest
amounts: Nitrogen, Phosphorus, and Potassium
The numbers on the synthetic commercial fertilizers refer to the
percentage content of the primary essential nutrients. The
sequence is NPK - the chemical symbols for Nitrogen, Phosphorus
and Potassium. (The chemical symbol for potassium is "K")
- SECONDARY ESSENTIAL NUTRIENTS: those essential nutrients that
are usually added by the grower but needed in smaller amounts:
Calcium, Magnesium, Sulfur
The essential micro-nutrients or "trace elements" that are needed by
most plants but are only needed in very small quantities; they are
usually grouped as cations or as anions
- CATIONS: Found in nature in the cation form . . . that is as
ions that have a positive charge because they have given up one
or more electrons: Iron, Copper, Zinc, Manganese, Cobalt
- ANIONS: Found in nature in the anion form . . . that is as an
ions that have a negative charge because they have picked up
one or more extra electrons: Chlorine, Boron, Molybdenum
"CHEMICAL" VS. "ORGANIC" FERTILIZERS:
It is obvious from the list of macro and micro nutrients that the
CONTENT of fertilizers is clearly chemical. These many chemical
elements are essential to the life and growth of the plants. Organic
materials such as the various manures, meals, composts, etc. can be
analyzed in a laboratory for their chemical content and those same
chemical elements are present. The atom or ion of any of these
chemical elements is totally the same whether it comes from a
synthetic or a natural source.
There are many unanswered questions in plant nutrition but, in
essence, the process starts in the roots and not with the fertilizer.
Roots exude a goo that is also a nutrient for many of the soil
organisms and the goo attracts the soil organisms in large numbers.
The goo essentially coats the root surface without going into the
soil. The various nutrients contained in the bodies and exudates from
the soil organisms becomes incorporated first into the goo and then
into the root structures to become nutrients for the plants.
The bottom line is Rodale's original thesis, "The best way to feed
the garden is to feed the soil organisms"
- Section C; FAQ: "Composting & Use of Compost"
- Section D; FAQ: "Plant Nutrition"
- Brady: "The Nature & Properties of Soils":
Chapter 13: "Nitrogen and Sulfur Economy of Soils"
Chapter 14: "Soil Phosphorus and Potassium"
Chapter 15: "Micro-nutrient Elements"
Chapter 16: "Practical Nutrient Management"