Perspectives on composting from UGACR

Why compost?

  • Produces nutrient rich soil
    • Compost contains a wide span of macro and micronutrients in a slow release form.
    • Compost buffers the soil which brings pH levels to the optimum range for nutrient availability for plants.
  • Improves soil structure
    • Compost helps bind clusters of soil particles together, which creates good soil structure. This enables soil to hold the proper ratios of air, moisture and nutrients. Good soil structure makes it loose enough to facilitate root growth but aggregated enough to reduce erosion.
  • Nurtures soil biology.
    • Beneficial bacteria, fungus, insects, and worms exist in healthy soil that supports plant growth. Proper compost will promote the growth of these organisms.
  • Reduces our dependency on synthetic fertilizers.
    • Decreased use of synthetic fertilizers reduces runoff pollution to nearby waterways.

At the UGA Costa Rica organic farm, we use three different compost systems to take advantage of limited space and meet the high demand for nutrient rich soil.

Small Pile Composting System:

We want to provide the optimal conditions for thermophilic composting because high temperatures promote rapid decomposition and kills weed seeds and disease-causing organisms.

Microorganisms secrete enzymes that break down organic compounds. Heat is a by-product of microbial activity. These broken down compounds are then absorbed into the cells of the bacteria and fungi. Throughout the decomposition process, nutrients are released and recycled in various chemical forms through the microorganisms and eventually become available for plant uptake.

Figure 1-1, below, shows the three temperature phases the compost pile goes through:

Compost graph
Source: “The Science of Composting.” THE SCIENCE OF COMPOSTING (n.d.): n. pag. Cornell University. Web. 12 July 2015.

What goes in?

The goal is to create a balance between carbon rich “brown” materials and protein rich “green” materials.  We want a to achieve a C:N ratio around 30:1 (30 parts carbon for one part nitrogen by weight).  In general, if you add vegetable waste or other “green” materials, mix in some leaves or wood shavings too.

  • Protein rich “green” materials: fresh manure, fish waste, lawnmower clippings, fresh green weeds, seaweed
  • Carbon rich “brown” materials: hay, straw, shredded leaves, maize stalks, shredded bark, sawdust

At UGACR, we use:

  • raw food scraps (fruit peels, vegetable waste, weeds, eggshells*)
  • leaves from the forest floor
  • used animal bedding (wood shavings + manure)
  • water
  • Effective Microorganisms
  • Other suggested materials: grass clippings, seaweed, wood ash, coffee grounds, tea leaves, newspaper, cardboard, wood chips, weeds, straw, litter, dirt or corn stalks.

What not to put in your compost:

  • citrus rinds*, eggshells*
  • meat, bones, fish scraps, dairy products (they will attract pests)

*debatable, some say add it, some say don’t

Food ScrapsProcedure:

  1. Start a new small pile by mixing ingredients listed above. In the UGACR garden, we get a delivery of food scraps from our kitchen such as watermelon rinds, eggshells and unused cabbage leaves.
  2. Chop up any big food particles with a spade.
  3. Mix in any garden scraps at this time; leaves, manure.
  4. Add one watering can of water if soil feels dry.
  5. Apply Effective Microorganisms.
  6. Eventually you will have made several different piles over time. Turn the oldest pile into a vermicompost bin or use it in your garden.
  7. Turn the newer piles every 4-5 days by shoveling each pile to where the previous pile sat and make room for a new pile with the freshest ingredients. At UGACR, our system looks like a semi-circle of piles.

Worm Compost

The same exact system can be used with the addition of worms, however, you are not trying to achieve high temperatures in vermicomposting. You will need to put the compost in a container so the worms cannot escape. You will also need a method of sifting out the worms when you are ready to harvest your compost.

  1. After 4-5 rotations on the ground (this takes about 1 month), the oldest compost pile is transferred to a vermicomposting bin where worms breakdown any leftovers.
  2. After 1-2 months we sift out the worms and have our final product.
  3. Add compost to garden and enjoy organic produce!

What should it look like when it is finished?

Compost is ready for use when the temperature in the pile drops to room temperature. It should:

  • smell earthy – not like ammonia;
  • no longer heat up after being turned or watered;
  • look dark and crumbly with no identifiable food items.

Why turn the pile every 3-5 days?

Bacteria require oxygen for respiration.  Turning the pile gives the bacteria sufficient oxygen so they can undergo the process of aerobic decomposition.  Without enough aeration, your compost will break down slowly and be slimy and stinky.  The piles can be left for longer but by turning more frequently we are producing a new temperature peak.

What’s this C:N ratio business?

Microbial cells are made up of about six parts carbon for every one part nitrogen (6:1).  We need to add a little more carbon than 6:1 to provide the energy for metabolism and synthesis of new cells.  We want a to achieve a C:N ratio around 30:1 (30 parts carbon for one part nitrogen by weight) in our compost because it provides a properly balanced diet for the microbes.  Wood shavings and newspaper are examples of ingredients rich in carbon, whereas, grass clippings and green weeds are examples of nitrogen rich ingredients.

In general, if you add vegetable waste, mix in some leaves or wood shavings too.  This will help reduce smells and keep the C:N ratio balanced.

You can add weeds to your compost pile?

Yes, a good pile will generate enough heat to kill weed seeds. Just remember:

  • Make sure your compost is hot enough (130 – 150 degrees F). If you reach your hand into the center of the pile it should feel almost too hot for comfort.
  • Mix your pile. While your compost may be hot in the center, the outside is cooler giving seeds a chance to survive.

I am in college with no yard space; how can I compost?

Make an Indoor Compost Bin

Blog post submitted by Lauren Fedenia, UGACR Sustainable Agriculture Intern.

One thought on “Perspectives on composting from UGACR

  1. Hey,

    Thanks a lot for this info. I recently moved to Costa Rica and will growing an organic garden for personal use. This page has been extremely helpful however I have more questions. The Effective Microorganisms that you talk about, do you offer that for purchase? If not, where would you recommend buying charcoal? That sounds like a lot of work to be honest but that’s why we moved here after all. I’ve never been much of a gardener but this is a new chapter of my life. Thanks for your support.


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