COMPOSTING PRACTICES AND PROCEDURES What is
compost?
Compost is fine-textured humus, which is an end product from the natural decomposition
of plants and plant products under controlled conditions.
Why Compost?
Composting is the most practical and convenient way to handle your yard refuse
because it is easier and cheaper than bagging or taking refuse to a dump site. Compost also
improves your soil and the plants growing in it.
Requirements for Efficient Decomposition
Decomposition of organic material in the compost pile depends on maintaining microbial
activity. Any factor that slows or halts microbial growth also impedes the composting process.
Efficient decomposition occurs if aeration, moisture, particle size, and nutrient levels
(nitrogen) are maintained for optimum microbial activity.
a. Aeration - Oxygen is required for microbes to decompose organic wastes efficiently. Some
decomposition occurs in the absence of oxygen (anaerobic conditions); however, the
process is slow, and foul odors may develop.
b. Moisture - Adequate moisture is essential for microbial activity. A dry compost will not
decompose efficiently. Proper moisture encourages the growth of microorganisms that break
down the organic matter into humus.
c. Particle size - Grinding the organic material before composting greatly reduces
decomposition time. The smaller the size of an organic refuse particle, the more quickly the
microbes can consume it.
d. Temperature - Temperature of the compost pile is very important to the biological activity
taking place. Low outside temperatures slow the activity down, while warmer temperatures
speed up decomposition.
Materials for Composting
Almost any organic plant material can be used for composting, including grass
clippings, leaves, twigs, chipped brush and old vegetable or flowering plants.
Vegetable peelings and coffee grounds can also be composted.
Many organic materials are suitable for composting. However, organic materials
containing both carbon and nitrogen in varying amounts (used by the microorganisms for energy
and growth) are preferred.
a. Carbon-Nitrogen Ratio
Microbial activity is greatest when the carbon-to-nitrogen ratio (C/N) is 30:1. For proper
decomposition the nutrients in the compost heap should be in the right proportions. The
carbon:nitrogen (C/N) ratio will determine how long decomposition will take. When the
decomposing organisms do not have the proper diet of carbon, the organisms may lose nitrogen
to the atmosphere as ammonia. If the initial carbon portion is too high in the compost heap, the
process will be considerably slower and very inefficient.
(The higher the number, the higher the carbon content and the longer the breakdown time.)
Table 1. Carbon to Nitrogen Ratio of
Common Composting Materials
Food waste 15:1 Leaves 60.1
Wood 700:1 Fruit waste 35:1
Sawdust 500:1 Rotted manure 20:1
Straw 80:1 Cornstalks 60:1
Grass clippings 19:1 Alfalfa hay 12:1
b. Organic Refuse Materials
Yard refuse, such as leaves, grass clippings, straw, and non-woody plant trimmings can
be decomposed. The dominant organic waste in most backyard compost piles is leaves. Grass
clippings can be decomposed; however, with proper lawn management, clippings do not need to
be removed from the lawn. Kitchen wastes such as vegetable scraps, coffee grounds and
eggshells may also be added.
c. Fertilizer and Lime
Microbial activity is affected by the carbon to nitrogen ratio of the organic waste.
Because microbes require a certain amount of nitrogen for their own metabolism and growth, a
shortage of nitrogen slows down the composting process considerably. Material high in carbon
and low in nitrogen, such as straw or sawdust, decomposes very slowly unless nitrogen fertilizer
is added. Even tree leaves, which are higher in nitrogen than straw or sawdust, can still benefit
from nitrogen fertilizer.
Composting Structures
To save space, hasten decomposition, and keep the yard looking neat, contain the
compost pile in some sort of structure. Structures can consist of a variety of materials and can
be made as simple or complex as desired.
Types of Structures
A barrel or drum composter generates compost in
a relatively short period of time and provides easy turning
(Figure 1). It requires at least a 55-gallon barrel with a
secure lid. Be sure that the barrel was not used to store
toxic chemicals. Drill six to nine rows of one-half inch holes
over the length of the barrel to allow air circulation and
drainage of excess moisture. The lid can be removed after
turning to allow for air penetration. Ideally, the compost
should be ready in two to four months. The barrel
composter is an excellent choice for the city dweller with a Figure1. Barrel or Drum Composter
relatively small yard.
Figure2. Circular Bin
For larger quantities or organic waste, bin
-
type structures are the most practical.A circular
bin can be made by using a length of small
spaced woven wire fencing held together with
chain snaps (Figure2).
Figure3. Three-Chambered Bin
A very efficient and durable
structure for fast composting is a
three-chambered bin (Figure .3)It
holds a considerable amount of
compost and allows good air
circulation. The three-chambered bin
works on an assembly line idea,
having three batches of compo st in
varying stages of decomposition.
Location
Locate the compost pile close to where it will be used and where it will not interfere with
activities in the yard or offend neighbors. Examples of good locations for the pile include areas
near the garden or kitchen or between the garage and house. The pile will do best where it is
protected from drying winds and where partial sunlight will help heat the pile. The more wind
and sun to which the pile is exposed, the more water it will need.
Preparing the Compost Pile
Figure 4. Layering
Prepare the compost pile in layers to facilitate proper mixing. Figure 4 illustrates the
layering process. Each pile ideally should be about five feet high.
Steps to follow include:
1.) Coarser materials decompose faster in the bottom layer. The coarse material also
allows air circulation around the base of the pile creating a chimney effect that will take air up
through the pile and heat it up. Moisten all layers as they are put in the pile.
2.) Organic wastes, such as leaves, grass, and plant trimmings are put down in a
layer eight to 10 inches deep. This layer should be watered until moist, but not soggy.
3.) Apply about a one-inch layer of soil or completed compost on top of the fertilizer
layer. Adding soil ensures that the pile is inoculated with decomposing microbes. In most cases,
organic yard wastes such as grass clippings or leaves contain enough microorganisms on the
surface to bring about decomposition.
4.) Place the nitrogen source on top of this layer. Use two to three inches of livestock
manure or a nitrogen fertilizer, such as ammonium sulfate, at a rate of one-third cup for every 25
square feet of surface area. If these nitrogen sources are not available, one cup of 10-10-10
fertilizer per 25 square feet of surface area will also suffice. Do not use fertilizer that contains a
herbicide or pesticide. Other organic sources of nitrogen are green grass clippings, lake plants
or blood meal.
Repeat the sequence of adding coarse material, organic waste, soil and fertilizer until
the pile is completed. Remember to water each section as you make the pile.
Maintaining the Compost Pile
To prevent odors and hasten decomposition, turn the pile once a month. Turning also
exposes seeds, insect larvae and pathogens to lethal temperatures inside the pile.
When the compost is finished, the pile will be about half its original size and have an
earthy smell to it. Table 2 lists additional composting problems and their solutions.
Table 2. Troubleshooting guide to composting problems.
Symptom Problem Solution
The compost has a bad odor. Not enough air. Turn it. Add dry material if the pile
is too wet.
The center of the pile is dry. Not enough water. Moisten and turn the pile.
The compost is damp and Too small. Collect more material and mix the
warm only in the middle. old ingredients into a new pile.
The heap is damp and sweet Lack of nitrogen. Mix in a nitrogen source like fresh
smelling but still will not heat grass clippings, fresh manure, or
up. blood meal.
Does compost have a nutrient value?
Yes. Compost slowly releases a small amount of plant nutrients, but it won't substitute
for fertilizer, particularly for nutrient-demanding plants like annual flowers and vegetables.
Gardeners often need to supplement the compost with a granulated fertilizer, like 10-10-10, or
an organic fertilizer, like composted animal manure.
When is compost ready to use?
Compost is ready when it looks like rich, crumbly earth and the original plant material is
no longer recognizable. Each time the pile is turned, some ready-to-use compost should be
available for harvesting from the bottom of the pile. Some gardeners screen their compost by
sifting it through a mesh screen. Any organic materials that have not fully decomposed are
added back to the pile to continue decomposing.
How can I use compost?
Compost can be used in the landscape and vegetable garden. Before planting, place 3 inches
of compost on the soil surface and incorporate it to a 12-inch depth. Compost also can be used
as mulch on the soil surface. Avoid using pure compost for containerized plants because its high
levels of organic acids and salts may damage roots. It also tends to dry out more quickly than
growing media containing peat moss, vermiculite and other waterabsorbing substances. It's best
to use prepared growing mixes obtained from garden centers for containerized plants.
RISK AND REWARD OF RECYLING IN PLANT NURSERY
Reusing growing media can turn your operation more eco-friendly, but don’t let your
plants suffer from improper practices.
The demand, use and need of growing media worldwide is increasing due to the
increased production of plants in containers and controlled environments. An industry that once
primarily served the floriculture and ornamental nursery industries now serves a booming
industry of container grown vegetables, cannabis, herbs, leafy greens and small/soft fruit. The
future is very promising and strong for the continued need of various growing media
components as more and more countries become more advanced in growing crops in
containers, and as more and more different crops around the world begin to be cultivated in
places other than the field. With increased demand and use comes increased interest by some
to recycle or reuse their growing media, otherwise it has to be disposed of in some way. A
practice that is as old as our current greenhouse industry, the reuse or repurposing of growing
media has been met with rewards as well as some serious challenges by different individuals.
Figure 1
A common practice of in ground (mineral) soil cropping systems involves the solarization
of soil planting beds, common for cut flower production, when (A) fallow soil (after a crop
production cycle) is covered with (B) transparent polyethylene tarps and allowed to heat via the
sun until sterile. Soil carts (C and D) are also often used for loose-fill soil and soilless substrates
prior to use, or reuse in crop production.
Photo courtesy of Brian E. Jackson
Figure 2
Nursery(and sometimes greenhouse/flower) operations often stock-pile (A and B) overs,
rejects, damaged, and unsold plants and attempt to repurpose them by (C) grinding in a tub
grinder (or like devise) and (D) piling or windrowing the material for some period of time before
being reused in future crop production. Photo courtesy of Brian E. Jackson
Figure 3
Recycled organic substrate materials stored outdoors can often contain weed seeds
(and pathogens) if not aged properly. Photo courtesy of Brian E. Jackson
Figure 4
Some greenhouse operations have implemented successful substrate recycling
programs that include (A) grinding root balls followed by steam sterilization of processed
substrate. The steam heated processed substrate materials (B and C) can then be aged or
stored until being incorporated back into the crop production cycle. Photo courtesy of Brian E.
Jackson
Sterilization – the temporary destruction of most all living organisms including microorganisms,
bacteria, fungi/spores, nematodes, insect eggs, weed seeds, etc., using heat of at least 212° F
for at least 30 minutes.
Sterile – free from most harmful pests or diseases commonly problematic for cultivated plants.
Can be achieved without steaming/heating and does not eliminate all microorganisms/biology in
the soil/substrate.
Solarization – the use of the sun’s energy to heat soil/growing media that is covered in a
transparent polyethylene tarp and allowed to heat to at least 160° F. This can be for short time,
30 minutes or over the course of weeks, depending on the setup and operation (Fig 1).
Sanitation – a condition, situation or environment that is free of harmful pests.
Pasteurization – a process of making something free from most forms of bacteria,
microorganisms, diseases, weed seeds or other forms of life. This is typically achieved with
steaming to a temperature of about 180° F for 30 minutes.
Potential risks
Recycled growing media can have some detrimental properties that should be
considered and monitored. First is the potential loss of physical properties of reused media.
Over time, organic particles naturally break down (decompose) thereby decreasing structure
and air porosity. If materials are ground up or otherwise handled during sterilization processes,
the particle size will continue to reduce therefore changing the physical properties when
repotted. Blending in some new growing media with the old/reused would likely help with this
problem.
Secondly, reused growing media can house potentially harmful pathogens, pests and
other unwanted goodies if not properly sterilized. The infection or exposure that improperly
recycled materials can have on an operation can be very detrimental to future crops and
cropping cycles. Recycled materials left outdoors can easily be contaminated with weed seeds
(Fig. 3) and/or pathogens. Recycled materials not properly sterilized could contain Pythium,
Fusarium, Phytophthora and other plant-sensitive diseases.
Lastly, there can be some toxicity effects from reused growing media. Mostly in the form
of residual fertilizer salts that can create high EC in mixes when re-blended or reused in future
crop productions. This can alter fertility practices and management as well as crop growth
response and control. Desalinization via washing or flushing with hot water is needed to remove
potential salts from materials like coco coir.
Potential rewards
If done properly and monitored, the reuse and recycling of growing media can save
money for some growers if they are willing to invest the time and resources to properly do it.
Growing media is often not cheap, so it is possible to save some money.
Reuse of materials is also a great way to reduce the disposal of organic and inorganic
materials, and make operations more sustainable and carbon-neutral.
Some cut flower growers and others have the process of recycling their growing media
down to a science and have been very successful for many years incorporating it into their
growing systems (Fig. 4).
With all of the “re-” words listed in the beginning of this article to describe growing media,
the one that should be considered most is respect. Your growing media is such a vital part of the
success of your production system, be that large or small, professional or hobby market. If you
reuse or recycle, do it right and understand the potential consequences. Cutting corners or
trying to save a dollar may be worth it on some things, but do not jeopardize the quality and
performance of your growing media!
