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New Vegetable Gardener — Compost and Composting

Compost Happens! Compost is the result of natural decomposition of organic matter. Take a walk in the woods and turn over a pile of leaves. That dark “earthy” material that has no unpleasant smell and doesn’t look anything like the parent material it was made from is called “compost.”

We are nearing the end of the vegetable gardening season now that the rainy season is not too far off. The high temperatures we have been experiencing are starting to affect your vegetable plants. Flowers are starting to fall off and fewer fruits are forming now. Soon you will have quite a bit of organic material (spent plant material from the garden). So why not recycle those materials from your vegetable garden, and vegetable scraps from the kitchen, back into the vegetable garden? Make your own compost.

Actually you are becoming a microbe “farmer” once you start composting. You will control the food the microbes will convert to compost. You will control the water, air and temperature so they will have an environment ideal for making compost. When done correctly, you will be able to make compost faster than nature would have done.

Composting is part of the Florida-Friendly Landscaping™ Principle #7, Recycle Yard Waste. Landscape and vegetable garden maintenance create lot of organic waste material. Decomposed (composted) organic matter releases nutrients back to the soil. Composting will also build soil structure that will aid in retaining moisture and nutrients in the root zone longer. Additionally, less material will be going to the landfill.

Composting is a natural process that changes organic waste materials into a valuable humus-like material called compost. These organic waste materials could be grass clippings, food scraps, vegetable plants no longer productive, leaves, animal manures and other products we will discuss later. These organic waste materials stimulate beneficial soil microorganisms (microbes), improve the ease with which we can work the vegetable garden soil (tilth) and the ease with which soil breaks down to improve the underground activity of plants and soil organisms (friability).

How do you get started? You could go to the garden center and purchase a compost bin. The minimum size should be about 27 cubic feet (3’x3’x3’). Most manufactured compost bins are not this large. They will make compost but will not generate enough internal heat to deal with weedy seeds and diseased plants so keep them out of small compost bins. You could make your own with about 12’ of 3’ high wire fencing with holes about 2-3” square. You can shape this into a cylinder that will be approximately 27 cubic feet. It will cost only a few dollars and last for years.

Now that you have your compost bin, you need to start adding organic materials to it. Start with about a 3-6” layer of brown materials. Brown materials (high carbon) are leaves, twigs, shrub trimmings, straw, etc. They decay slowly and tie up nitrogen in the soil if not fully composted. They add porosity (air filled space between particles) to the compost. Then add a 1-3” layer of green materials. Green materials (high nitrogen) are grass clippings, vegetable plant waste, kitchen waste, coffee grounds, etc. They decay rapidly, cause foul odors when compacted and supply nitrogen for composting. The next layer will be some sandy soil from your backyard. One teaspoon of good garden soil contains 100,000,000 bacteria and 800 feet of fungal threads (microbes). So there is no reason to shop for compost activators on the web. You have all you need in your soil. Finally, water these brown, green and soil materials thoroughly. If the compost pile is too dry, the microbes slow down or stop working. If the pile is too wet, oxygen may be driven from the pile and things will start to stink. The right amount of water is applied when you grab a hand full of compostable materials and squeeze them. They should feel like a damp sponge. Repeat the above process until the compost bin is full. This will take some time.

What should you put in the compost bin? A good rule of thumb would be use “anything that was once growing in the ground.” Here is a short list: leaves, paper, straw, animal bedding mixed with manure, vegetable scraps, grass clippings, coffee grounds and animal manures from “plant eaters” only such as cows, horses, chickens and elephants should the circus be in town.

What should you not put in the compost bin? Here is a short list: meat scraps, fats or oils, diseased plants, seedy weeds, recently fungicide-treated plants, citrus and wood ash (affects the pH of the pile if too much is used) and egg shells unless they are washed and finely ground to a powder (otherwise, leave them out). Dog, cat and pig manures should also be left out of the compost bin.

For those of you who like details and math, compost will happen at its fastest rate when the ideal carbon-to-nitrogen ratio (C:N) is equal to 30:1. You can calculate you C:N ratio based on the materials  you use. Just browse the internet and look for the C:N ratio of those materials. For example dry, non-legume hay has a C:N ratio of 40:1.0-1.5. Coffee grounds have a C:N ratio of 25:1. Kitchen scraps have a C:N ratio of 10-20:1-2. If I had 50 pounds of this hay, 10 pounds of kitchen scraps and 2 pound of coffee grounds, I could calculate the actual C:N ratio of these mixed materials.

50 lbs hay x 40% C = 20 lbs. C
10 lbs Kitchen scraps x 10% C = 1 lb. C                    20 + 1 + 0.5 =21.5 Total C Value
2 lbs Coffee grounds x 25 % C = 0.5 lb. C

50 lbs hay x 1% N = 0.5 lb. N
10 lbs kitchen scraps x 1% N = 0.1 lb N                     0.5 + 0.1 + 0.02 = 0.62 Total N  Value
2 lbs coffee grounds x 1% N = 0.02 lb N

21.5/0.62= 34.7 parts carbon to 1 part nitrogen or C:N ratio = 34.7

You could change the amount of material until you get exactly C:N ratio = 30:1 but 34.7 is close enough for me.

Active composting occurs in the temperature range of 55ºF – 155ºF in the compost pile. If you have a good mix of browns and greens, in a few days you should notice that the temperature in the pile is increasing. If not, add some granular fertilizer to increase the nitrogen content of the mix. Because of this natural heating, do not add earthworms to the compost pile. They will not survive.

To increase the rate of decomposition, you should turn the pile (use a pitchfork) every 5-7 days. You can open the wire cage and move it next to the pile. Then mix the materials when you refill the wire cage and don’t forget to add water if necessary. During the rainy season, you may want to put a tarp over the pile to keep excess water out of the pile. Do not be tempted to add more materials to the pile as it shrinks. If you do, you will not know when the composting is finished. If you have additional materials, start another compost pile/bin.

The compost pile will reduce in size to about 1/3 of its original volume. When the material no longer heats up after mixing, allow it to mature/cure for at least four more weeks before you use it. Compost is mature when it is dark brown in color, crumbly, has an earthy smell and you cannot readily recognize the material that it was made from.

Use the mature compost as a soil amendment; it has little value as a fertilizer due to the low and inconsistent levels of nutrients in compost. Continue to add fertilizers for plant growth. Use compost as a mulch. Increase the potting mix in container plantings by adding up to 1/3 compost by volume to the potting mix before adding it to the container.

There will be times where the compost pile will smell, not heat up, become too wet or become too dry. Turning the pile with the pitch fork is a good starting place for all of these issues. Raccoons, rats and insects in the compost pile are much more difficult to deal with. Make sure you have not put meat scraps, fatty food wastes or egg shells in the compost pile. If you have, remove them and whenever you add new kitchen waste to the pile, bury it several inches below the top of the pile. Some commercial compost bins have twisting top lids and large nylon screws to screw into the ground to keep animals from getting under the pile.

Don’t get too excited when you see mites, snails, slugs, millipedes, sowbugs, beetles, bugs or whiteworms in the compost pile. They are grinding and chewing the organic materials to make them smaller for the microbes to more easily work on them. Composting is all about managing the right amount of air, water and “food” to keep the work crew (microbes) happy.

For more information about composting visit the UF/IFAS Extension Sarasota County webpage.