Just like in commercial composting facilities, conditions in home bins affect the rate at which organic materials and compostable products break down. Certain composting conditions and practices are recommended to optimize the breakdown of all composted materials, including certified home compostable products.
All bin types can successfully produce compost conditions that effectively break down kitchen food scraps and certified home compostable products, so the choice of bin type and size comes down to individual preference, space, and management style. Four general types of systems exist: closed bins; open stationary bins; tumblers; and insulated bins. Personal composting habits can be adjusted to make any bin type work well, but closed bins and open stationary bins usually create conditions that are closer to ideal for composting certified products. Small tumblers and insulated bins may require higher levels of management to produce the biological conditions that foster optimal breakdown of compostable products. Generally, the larger the bin size, the easier it is to create and maintain ideal composting conditions.
Feedstocks are the materials that are put into a compost bin. The material types, sizes, and amounts added to the compost bin all impact the composting process.
Reducing the size of feedstocks increases the surface area available to microbes and accelerates product disintegration. Larger materials—including certified home compostable products—can be torn, shredded, or chopped before putting them into the bin for faster disintegration.
Dry leaves, fresh green yard waste, and food waste are common feedstocks for compost. “Browns,” such as dry leaves, wood chips, and compostable products, are sources of carbon. “Greens,” such as fresh yard waste and food scraps, are sources of nitrogen. The optimal ratio of carbon to nitrogen feedstocks is 25-30 parts carbon to 1 part nitrogen, but an acceptable compost recipe may vary from 10:1 to 30:1 carbon to nitrogen. C:N ratios lower than 10:1 (common for home composters that prioritize food scraps but don’t have a large yard) may cause odors and a “slimy” appearance. When greater than 30:1 it may slow or impede the composting process.
Some compostable products may come into contact with meats, fats, or dairy products. While these items can be safely composted, they have greater potential to introduce complicating factors such as odor, pests, and pathogens. Home composters should think carefully about adding these particular food products or compostable products that have come into contact with them. Each composter is responsible for educating themselves on the risks and benefits of including these types of feedstocks, as optimal conditions and high management levels are necessary for compost to reach temperatures sufficient to mitigate pathogenic risk. It can be time and management intensive to produce these composting conditions.
The moisture level in the compost pile should ideally be maintained at a constant 50% or greater. Piles should be watered or covered to control the moisture content. Moisture levels below 30% will slow down the biological activity needed to break down feedstocks and home compostable products
Maintaining the proper balance between moisture and oxygen is key to successful composting. Utilizing a bin with air holes or an aeration tube(s) can passively add oxygen, while regularly turning the material in the bin will actively introduce oxygen. A pile that’s too wet will likely not have enough oxygen, which would cause the decomposition to change from aerobic (with oxygen) to anaerobic (without oxygen) and become foul-smelling.
Thoroughly mixing the compost materials at least monthly is recommended in order to distribute the materials, oxygen, and water throughout the pile. Mixing the pile should reinvigorate microbial activity, causing the compost temperature to rise. Piles can be mixed more frequently than once per month, such as when fresh feedstocks are added, but shouldn’t be mixed more often than every few days, as this may release too much heat and disrupt beneficial microbial and fungal growth.
The biological activity of microbes that are consuming the feedstocks inside a compost pile creates heat, so an active compost pile will be warm or hot. Adding fresh feedstocks, turning the pile, or adding water can reinvigorate microbial activity, causing a rise in temperatures inside the pile. Decomposition will occur most rapidly when internal pile temperatures are >90, and while higher temperatures seen in commercially operated compost piles (e.g. 150 °F ) are less typical in home compost, they are possible. Testing for certification of home compostable products is done conservatively at lower temperatures of 68-86°F.
Outside ambient temperature will affect heat retention of the compost pile, especially in small home compost bins with less mass to hold the heat, and cold temperatures will decelerate the composting process. However, management practices can help mitigate the effects of colder weather to keep composting active, if slower, year-round. Prolonged cold ambient temperatures may ultimately stall the composting process (and even freeze the material in the bin), but warmer temperatures will resume microbial activity in the compost pile.
All composting feedstocks, including leaves, avocado pits, banana peels, and certified home compostable products, will fragment into increasingly smaller pieces as they break down into carbon, water, and organic matter in a home compost pile. Maintaining optimal conditions will accelerate this decomposition of compostable products and organic materials. However, the timeframe required for compostable products and tougher organics to fully integrate into compost will vary widely, depending on the composting conditions, and may take up to 12 months or longer to fully break down. This is similar to how different types of food scraps break down at different rates; for instance, a banana peel will typically degrade faster than an avocado pit. Disintegration tests for certified home compostable products require that products break down within 6 months.
Home composters can evaluate these management variables using simple techniques:
Following these recommended practices will help to ensure that microorganisms and fungi needed to break down compostable products are able to thrive. While BPI has certified products for home compostability, composting results are not guaranteed, as they are reliant on robust composting conditions and management practices to break down. Not maintaining these recommended conditions can prolong or prevent successful composting and product breakdown.
The following organizations provide additional online information on how to compost at home:
Institute for Local Self-Reliance: https://ilsr.org/composting/home-composting/
Cornell Waste Management Institute: https://cwmi.css.cornell.edu/smallscale.htm
Ohio State University Extension: https://ohioline.osu.edu/factsheet/hyg-1189-99
Penn State Extension: https://extension.psu.edu/home-composting-a-guide-for-home-gardeners
Rutgers University Extension Service: https://njaes.rutgers.edu/fs811/
University of Minnesota Extension: https://extension.umn.edu/managing-soil-and-nutrients/composting-home-gardens#compostable-materials-882312
U.S. Department of Agriculture: https://www.usda.gov/about-usda/general-information/initiatives-and-highlighted-programs/peoples-garden/food-access-food-waste/composting#:~:text=Get%20composting.,add%20water%20to%20keep%20moist
US EPA: https://www.epa.gov/recycle/composting-home
Composting classes are also often available through state extension services master gardener or master composter programs and through local governments. Check locally for programs near you, such as these Master Gardner Extension programs.
Before launching a Home Compostability Certification Program, BPI conducted field testing with thousands of home compostable product samples certified by other entities to collect comparable data on real-world composting systems and conditions across a variety of North American climates. This research was designed to explore how composting variables and management practices affect composting conditions and whether current home compostability standards are reliable indicators of real-world product performance. Data from this 6-month field study, combined with information from reputable home composting resources such as those listed on the Additional Resources webpage, were used to develop recommended home composting practices and conditions.
BPI’s field research found that across all tested home composting bin types (tumblers, closed stationary bins, insulated bins, and open stationary bins), average compost temperatures exceeded ambient temperatures. Average compost pile temperatures were maintained between 68°F-102°F, with temperature maximums measured as high as 122°F-140°F.Insulated bins and open stationary bins generally maintained higher average compost temperatures than tumblers and closed stationary bins, and more robust management practices contributed to higher pile temperatures and better heat retention compared to ambient temperature.
Compostable products are certified to science-based, globally accepted standards, such as NF T51-800 that BPI uses. Compostability standards require testing in laboratory conditions to ensure the tests are controlled, repeatable, and reproducible. This scientific approach results in tests that evaluate the attributes of the compostable product by keeping all other variables constant. Compostability standards were developed to be representative of real-world composting conditions to ensure that compostability testing accurately predicts that compostable products break down as expected in the appropriate composting environment.
Home compostability testing is conducted at 20-30°C (68-86°F) to conservatively simulate the typical biological operating conditions within a compost pile. This testing is intended to evaluate if a material can biodegrade under realistic mesophilic composting conditions by simulating a functioning home compost system during active decomposition. BPI’s field research found average compost pile temperatures to be between 68°F-102°F, which is further supportive of the temperatures used in lab testing.
Through this research, BPI found that management variables controlled by the home composter, such as the ratio of carbon to nitrogen inputs, moisture content, and frequency of turning the pile, all greatly impact the breakdown speed and thoroughness of food scraps, home-certified compostable products, and yard waste in a home compost bin.
While pile temperature is a key parameter in determining the success and speed of a composting system, ambient temperatures and the climate also affect composting.
Management practices such as larger bin sizes (at least 3 feet x 3 feet x 3 feet); using insulated bins; insulating winter compost piles with straw, tarps or leaves; reducing the frequency of turning; and maintaining proper moisture levels can help minimize the slow-down caused by cold ambient temperatures. Even if a compost pile freezes in the winter, the microorganisms will reactivate when the weather warms, and composting activity will pick up.
Moisture challenges in dry climates can be mitigated by watering the pile directly or using a bin type or covering that reduces evaporation.
The home composter can choose to try and mitigate environmental effects or wait for composting activity to naturally resume when nature provides the right conditions.
Learn more about why BPI developed its home certification program
