- Author: Help Desk Team
We have all heard of this magical stuff called compost. But what is it? Where does it come from? Why is it so important for our gardens? The reason compost is so important is because it enriches our soil, adding important nutrients that are used by plants for growth. When we create compost, we are breaking down organic matter into a form that provides a rich amendment for the soil and promotes healthy microbial activity. With these nutrients, plants can better resist disease and insects. In addition, compost increases water retention and helps reduce soil diseases. And it can be rewarding to make your own!
What do you need for great compost?
Green material—Yard waste, kitchen vegetable scraps, coffee grounds, or fresh grass clippings. This fresh waste provides the compost's nitrogen content. Do not add meat, dairy products, oil, fat, or dog or cat manure.
Brown material—Dried leaves, torn up newspaper, pieces of cardboard boxes, or shredded paper bags. This dry material provides the carbon content. The smaller you cut the pieces, the faster the composting process will be.
How much of each—Start with equal parts of green and brown material and add up to twice as much brown material as green. Don't use more green material than brown.
Water—Water each layer of the pile to the level of a wrung out wet sponge. If the bin is exposed to rain and gets too much water, you might need to cover it.
Air—Turn the pile every few days, if possible, but at least once a week for air circulation. A pitchfork works well for turning. In addition to letting the pile “breathe”, it helps prevent problems with flies and rodents. Turning the pile helps maintain an optimal temperature, while mixing prevents dense clumping of some materials such as wet green grass.
Temperature—Heat in the pile is generated by bacteria feeding on the green material. Temperatures above 140°F will kill many pathogens and weed seeds and will also accelerate decomposition for faster composting (see below). A compost thermometer with a long probe gives good information about when to turn the pile and when to water it.
Different methods of composting—Factors to consider when choosing a method include the time and energy needed to maintain the pile, the amount of compost needed, and the time needed to achieve the finished product. The pile needs to be at least 3 feet square to generate enough heat for decomposition. You can build the compost pile right on the ground but if you build a structure to contain the pile, it should be 3–5 feet with one side open for easy access to build or turn the pile. Sun or shade does not matter as the temperature of the pile depends on its composition, not exposure to the sun. Other composting containers can include a closed container, like a rolling barrel, or an open bin composter. There are many ways to make compost: underground, above ground, in bins, in boxes, in pits, in bags, in barrels, in strips, in sheets, and in trenches.
Slow composting method (easy but slow)—Continuously add materials to the pile with little or no chopping of materials. Bury ‘green' scraps 6–12 inches in the center of your bin to reduce attracting flies and rodents. Turn and water as desired for finished compost in 12 to 18 months.
Intermediate composting method (a little more work but faster)—Build a 3' x 3' x 3' pile with materials cut into 2-inch pieces. Turn and water the pile weekly without adding more material to get finished compost in 3 to 8 months.
Fast composting method (the most work but finished fastest)—Build a 3' x 3' x 3' pile with materials chopped to ½ to 1½ inch pieces. Check the temperature of the pile every day with a thermometer in the center of the pile. Turn the pile immediately if the temperature is 150 degrees F or above. Turn and water daily while the pile is between 140–150 degrees F. As the pile cools, turn it whenever it reaches 120 degrees F. Once the pile cools below 120 degrees F, turn and water every week for finished compost in 6–8 weeks.
When is the compost done? The pile will shrink, losing about 1/3 of its volume. It will be dark brown and crumbly with an earthy smell. You should no longer be able to tell what each of the individual ingredients was. Allow compost to age for two weeks before you add it to the soil around plants. Or incorporate it into the soil, but don't sow seeds or transplant seedlings for two weeks.
For more details about composting and what materials to use:
https://sacmg.ucanr.edu/files/163139.pdf
For information about how to use compost in the home garden:
https://ucanr.edu/sites/ccmg/files/221120.pdf
This video is from our own composting experts at our demonstration garden in Walnut Creek: https://www.youtube.com/watch?v=E77Yps9K2bw The garden is open to the public on Wednesday mornings April through October. Please stop by and ask questions.
We hope to see you at Our Garden!
Help Desk of the UC Master Gardeners of Contra Costa County (JRB)
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener of Contra Costa County
Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your question about compost.
You said that your compost bin is not getting hot. If the compost pile is not heating up, then the pile is too wet or too dry or there is not enough green material (or nitrogen) present. If too wet, the material should be spread out to dry. If too dry, add moisture to make it “spongy”. If neither of these, then the nitrogen is low and this can be corrected by adding materials high in nitrogen (lawn cuttings, etc.).
You asked whether you can place materials which are not fully composted into the garden bed. My comment was that yes this is possible, but that it will draw nitrogen from the soil to continue the composting process in the garden bed. Also, heat is the driving force to kill funguses or other living material in the pile prior to placing it in the vegetable bed.
We discussed making sure there is enough nitrogen present in the composting contents. The document linked below on rapid composting discusses this –
https://vric.ucdavis.edu/pdf/compost_rapidcompost.pdf
And here is a link on composting basics that you might also find informative:
http://sonomamg.ucanr.edu/composting/composting_basics/
Free Recycle Smart Compost Class: You might also be interested in the compost class offered by Recycle Smart. The class is free, and was developed to help residents understand the importance of organics recycling, build composting systems, recycle food and yard waste at their homes, build healthy urban soils and support thriving landscapes. For APPLICATION, dates and more information visit www.RecycleSmart.org/CompostSmart. The application deadline for the next class is February 22, 2019.
Good luck on your compost. Please do not hesitate to contact the Help Desk if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (MCW)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Thank you for contacting the UC Master Gardener Program Help Desk. It was nice to speak with you this morning. You asked about when to spread compost on your garden--whether you should do it now or wait until spring. There is no wrong time to put compost into the garden, but the microbes that decompose the compost and make nutrients available work much slower in the winter. As soon as the soil warms up, the microbes work faster. If you choose to wait until spring, make sure you apply it at least a couple of weeks before you plant.
Here's a link to information about rapid composting you might find interesting: https://vric.ucdavis.edu/pdf/compost_rapidcompost.pdf.
And more information about using compost in the home garden can be found at:
http://ccmg.ucanr.edu/files/221120.pdf.
Please don't hesitate to contact us again with further gardening questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ignore.edu/HortCoCo/ You can also subscribe to the Blog.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client's Request (via phone): What is the nutritional composition of compost tea?
Our research did turn up some information about compost tea that you might find of interest. Here's a link to a slide presentation on the “Nutrient Value of Compost” which appears to have been given at a symposium sponsored by the University of California in 2009: https://vric.ucdavis.edu/events/2009_osfm_symposium/UC%20Organic%20Symposium%20010609%2005b%20Hartz.pdf Slide 4 in the presentation shows typical nutrient levels of compost. As you'll see, the NPK (nitrogen-phosphorous-potassium)l nutrient levels vary depending on the source of the materials used to make the compost—for example, does the compost contain manures or only crop residues. Slide 17 in the same presentation notes that when the compost is diluted to make compost tea, the nutrient effect of using the tea is likely “insignificant”.
Another University of California source indicates that a potential benefit of compost tea is that the leaves of the plants may be able to directly absorb nutrients that are present in the tea for a quick nutrient boost. See: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13471. However, as you'll see if you further review the information at this link, that same UC source is skeptical about the disease prevention claims that are sometimes made for compost teas. The authors eventually conclude: “Plain old compost, not the tea, typically acts to release those same nutrients in a slower manner, plus it has the added benefits of cooling and cushioning the soil. So to really get the most out of your compost, perhaps it's best to apply it to the landscape, and let nature make the tea with rain or irrigation water, unless you have a specific need for a quick, but problematic, boost of nutrients.
We hope that this information is useful as you evaluate your use of compost tea. You are welcome to contact us again if you have other gardening or pest questions.
Help Desk of the UC Master Gardener Program ofCntra Costa County (TKL)
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Editor's Note: The editor has been following the use of compost tea for more than several years. While there is a lot of anecdotal enthusiasm for its use, conclusive scientific findings have yet to be made of its benefits. Prof Linda Chalker-Scott PhD of Washington State University has written extensively on compost tea. (click). If you are considering its use, the Editor recommends her various articles on its use. |
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/)
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
With my small garden, the beds fill to overflowing. Thus, I do not always apply all my compost. My question: Can compost “go bad?” if it dries out? If it is not used for months? Thank you!
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your compost question. You asked if compost would go bad if it dries out. The answer is not really, but it can change. If it completely dries, it may become a little difficult to wet the compost. You might want to moisten it before putting it into your garden.
When compost completely dries, many of the microorganisms (bacterial and fungi) will die, but some will form "survival capsules" or spores that will keep them alive until better conditions come along. Also, good soil is teeming with microorganisms that will "repopulate" the compost, and will continue to break down compost added to the soil.
So, compost that has dried is fine to use in your garden. It just needs some management. And congratulations on being a successful composter!
Please let us know if you have more questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/)
