Composting during cold weather presents unique challenges, from slowing microbial activity to managing frozen food scraps. Yet, with the right strategies and tools, you can maintain an efficient composting system throughout the winter. This guide provides technical advice for composting in low temperatures, offering specific instructions for various methods and actionable tips to keep your compost pile active. Whether you're new to composting or experienced, this guide has practical advice to ensure your compost thrives year-round.
Why Composting in Cold Weather Matters
Composting isn’t only a warm-weather activity. Winter composting preserves your routine, reduces waste, and provides ready compost for spring planting. Additionally, involving family members in holiday composting can turn the chore into a bonding experience—especially during seasonal cleanups and festivities.
General Tips for Cold Weather Composting
Maintaining an active compost in cold weather requires adjustments to your typical routine. Winter composting tips should be applied when outdoor temperatures consistently fall below 50°F (10°C). At this point, microbial activity begins to slow, and maintaining internal heat in the compost pile becomes crucial. Once temperatures drop near or below freezing (32°F or 0°C), the risk of the pile cooling significantly increases, making insulation and other cold-weather strategies essential to sustain decomposition. Here’s how to optimize your compost in freezing temperatures:
Insulation Is Key
Retaining heat is crucial for microbial activity because thermophilic bacteria, which drive the decomposition process, require elevated temperatures to thrive; when temperatures drop below their optimal range, metabolic rates slow significantly, leading to reduced breakdown of organic matter and stalling the composting process. Wrap your compost bin in insulating materials such as straw bales, old blankets, or tarp. For extra insulation, locate the bin near a windbreak or sunny spot.
Increase Pile Size
A larger pile conserves thermal energy more effectively due to its increased mass and density, allowing the core to remain insulated from cold external temperatures and sustain the microbial activity necessary for continuous decomposition. If you usually maintain a small compost, consider increasing its size during winter. Aim for at least 3 feet in height and width to generate and retain enough heat.
Layering for Efficiency
Strategically layering green (nitrogen sources) and brown (carbon sources) creates a balanced environment that supports microbial diversity and efficient decomposition. This balance facilitates consistent aerobic activity, which in turn generates and retains heat necessary for maintaining an active compost pile, even in cold conditions. If your compost goes anaerobic in the winter, the pile will likely cool down further, slowing decomposition to a near stop. Anaerobic conditions occur when there’s insufficient oxygen, causing a buildup of excess moisture and compacted materials. As a result, anaerobic bacteria take over, producing foul-smelling compounds like ammonia and hydrogen sulfide. The pile can also become too wet or frozen, which inhibits the activity of beneficial microbes, making it challenging to restore the compost’s balance until warmer weather returns.
Add More Greens
During cold weather, decomposition slows, making it harder for your pile to heat up. Add extra green materials like kitchen scraps to boost microbial activity. Increased microbial activity drives higher temperatures because as microorganisms break down organic materials, they release energy in the form of heat. This exothermic process, particularly when involving fast-metabolizing bacteria, intensifies with the availability of nitrogen-rich materials, leading to elevated temperatures within the compost pile. The heat generated creates a self-sustaining cycle where active microbes continue to thrive, further boosting the overall temperature and speeding up decomposition.
Turn Less Frequently
Turning your compost pile frequently in warm weather promotes oxygen flow, speeding up decomposition. However, in winter, excessive turning exposes the pile’s warm core to cold air, causing a rapid drop in temperature. This heat loss can slow down or halt microbial activity. To maintain the internal warmth that microbes need to remain active, it’s best to reduce the frequency of turning during cold weather. This approach helps insulate the pile and keeps the decomposition process steady despite lower outdoor temperatures.
Composting Methods for Cold Weather
Different composting systems have varying effectiveness during winter. Here’s a breakdown of five methods and how to manage them in cold weather:
1. Worm Composting (Vermiculture)
Worm composting relies on red wigglers, which thrive in temperatures between 55°F and 77°F. To keep worms active in cold weather:
Move Indoors: Bring the worm bin inside, ideally to a basement or heated garage.
Insulate the Bin: If indoor space isn’t available, insulate the outdoor worm bin with straw, blankets, or even bury it partially underground.
Adjust Feeding: Worms eat less in cold temperatures. Avoid overloading the bin with food scraps that could attract pests.
2. Compost Tumblers
Compost tumblers are convenient, enclosed systems that minimize exposure to external conditions. During cold weather:
Strategic Positioning: Place the tumbler in direct sunlight to maximize heat absorption.
Insulate with Straw or Foam: Wrap the tumbler in insulating materials to retain warmth.
Add Smaller Materials: Break down inputs into smaller pieces to speed up decomposition.
3. Three-Bin Systems
A three-bin system is ideal for large-scale composting and handles cold weather effectively with a few adjustments:
Consolidate Materials: Combine contents from all three bins into one large pile for winter. The increased mass retains more heat.
Cover the Pile: Place a tarp or old carpet over the bins to trap heat and moisture.
Add Fresh Manure: Fresh manure acts as a green material and generates additional heat, making it a valuable addition during winter.
4. Trench Composting
Trench composting involves burying organic material directly into the soil. It’s an effective, low-maintenance method for winter:
Bury Deeper: Dig trenches at least 12 inches deep to protect materials from freezing temperatures.
Compost Near Root Zones: Bury compost near plant root zones to prepare for spring growth. The slow breakdown over winter enriches the soil for planting.
5. Hot Composting
Hot composting is a method designed to maintain high temperatures for faster decomposition. While challenging in winter, it’s doable with some adjustments:
Add Heat Sources: Mix in fresh manure, coffee grounds, or even hot water bottles wrapped in plastic to boost internal temperatures.
Active Monitoring: Check the pile’s temperature regularly and adjust green-brown ratios accordingly. Keep the core temperature above 104°F (40°C) to maintain activity.
Holiday Composting: Turning Festivities into Family Bonding
The holiday season generates significant organic waste—from leftover food scraps to used wrapping paper. These materials are ideal for composting, and involving the family makes it a fun, shared activity. Here’s how to incorporate composting into your celebrations:
Designate a Compost Station: Set up a compost bin near your kitchen for easy access while cooking holiday meals. Label containers for collecting vegetable peels, coffee grounds, and other compostable waste.
Plan a Post-Meal Composting Activity: After holiday meals, gather family members to sort compostable items. Use this time to teach younger members about sustainability.
Incorporate Leftovers: If your family hosts large gatherings, food waste can be substantial. Rather than throwing away inedible leftovers, compost stale bread, spoiled veggies, and even used napkins.
Reduce Before You Rot
Food waste prevention and food rescue should always be prioritized over composting, as they address the root of the problem more effectively. Prioritizing these strategies helps minimize food waste at its source, which is more sustainable and resource-efficient. Food waste prevention involves practices such as careful meal planning and proper food storage, while food rescue focuses on salvaging edible leftovers and donating surplus food to those in need. Ideally, only inedible food should be composted, and in minimal quantities, to ensure that composting serves as a final step after all other waste reduction efforts have been exhausted. This approach aligns with source reduction principles, which emphasize minimizing waste generation rather than managing it after the fact.
Composting in cold weather is achievable with proper preparation. Focus on retaining heat, using appropriate methods, and adjusting your routine. As temperatures drop, let your compost pile rise to the challenge!
Let's Go Compost is a 501(c)(3) non-profit with a mission to make composting free and accessible throughout the United States. Our goal is to revolutionize waste management, reduce landfill waste, and combat harmful greenhouse gas emissions. Our programs are community-led with a focus on supporting school gardens and community gardens, all working to ensure composting and free food waste drop off sites reach all, irrespective of location or income.