Starting an On-Farm Composting Operation in California

Composting makes sense for California farms. You're turning waste into a valuable soil amendment, reducing disposal costs, and building the kind of soil biology that makes everything else work better. But it's not as simple as making a pile and waiting.

California has specific regulations for agricultural composting. The process requires attention to get right. And the benefits depend on producing quality material consistently.

At Agconnect, we've helped farms establish composting operations for over two decades. Our compost consulting service walks you through the entire process. Here's an overview of what's involved.

Why Compost On-Farm?

Economic benefits:

• Reduce organic waste disposal costs
• Create valuable soil amendments instead of buying them
• Potential revenue from excess compost sales
• Lower fertilizer costs over time as soil health improves

Agronomic benefits:

• Build soil organic matter—the foundation of soil health
• Improve water-holding capacity (critical in California)
• Feed beneficial soil microbes
• Provide slow-release nutrients
• Improve soil structure and tilth

Environmental benefits:

• Divert organic waste from landfills
• Sequester carbon in soil
• Reduce erosion and runoff
• Support sustainable agriculture certifications

California Regulatory Framework

Before starting any composting operation, understand the regulatory landscape.

CalRecycle Requirements

California's compost regulations fall under CalRecycle's jurisdiction. For on-farm composting, the key distinction is between:

Exempt activities (generally no permit needed):

• Composting only materials generated on your farm
• Small-scale operations (typically under certain tonnage thresholds)
• Meeting specific operational requirements

Permitted activities (require notification or permits):

• Accepting materials from off-site sources
• Larger scale operations
• Commercial compost sales

The rules have changed several times and vary by situation. We strongly recommend consulting with CalRecycle or your county environmental health department before starting.

Local Requirements

Counties may have additional requirements including:

• Land use permits
• Setback requirements from neighbors and water sources
• Stormwater management plans
• Fire department notification

Air Quality

In some air districts, composting operations require permits or must follow specific practices to control emissions. Check with your local air quality management district.

Site Selection and Design

Where you put your composting operation matters for efficiency, compliance, and neighbor relations.

Site Requirements

Location considerations:

• Adequate distance from neighbors and sensitive receptors (500+ feet recommended)
• Away from wells and water courses
• Good drainage to prevent ponding
• Year-round vehicle access
• Room for turning and curing

Infrastructure needs:

• Hardened surface (concrete, asphalt, or compacted base) or appropriate containment
• Stormwater management system
• Access to water for moisture management
• Equipment storage
• Possible weigh scale for tracking

Layout Design

Efficient layout minimizes handling and travel distance:

• Receiving area separate from active composting
• Windrow or pile orientation for turning equipment
• Curing area with adequate time capacity
• Finished product storage
• Traffic flow that doesn't cross-contaminate

Feedstock Management

Quality compost starts with quality inputs.

Common On-Farm Feedstocks

Carbon sources (browns):

• Grape pomace
• Orchard prunings (chipped)
• Straw and stalks
• Bedding materials

Nitrogen sources (greens):

• Manure (cattle, horse, poultry)
• Cover crop residues
• Vegetable waste
• Green prunings

Carbon-to-Nitrogen Ratio

The C:N ratio determines how well your pile composts. Target 25:1 to 35:1 for active composting.

• Too high C:N (above 40:1) → Slow decomposition
• Too low C:N (below 20:1) → Nitrogen loss, odors

Most farms need to balance high-carbon crop residues with higher-nitrogen manure or green materials. Getting this right is one of the main things we help with in our consulting.

Materials to Avoid

Some materials shouldn't go in agricultural compost:

• Diseased plant material (unless temperatures are achieved to kill pathogens)
• Persistent herbicide residues
• Excessive amounts of any single feedstock
• Materials that don't break down (plastic, glass, metal)

The Composting Process

Composting is managed decomposition. The key is maintaining conditions that favor beneficial microbes.

Active Phase

During active composting (4-8 weeks typically):

Temperature: Pile should reach 131-160°F within first week and maintain for pathogen reduction. Monitor with long-stem thermometer.

Moisture: Target 50-60% moisture content. Should feel damp but not drip when squeezed.

Oxygen: Turn piles when temperatures plateau or exceed 160°F. Static piles need forced aeration.

Turning frequency: Depends on system—windrows typically turned every 1-2 weeks during active phase.

Curing Phase

After active composting, material needs 4-8 weeks of curing:

• Temperatures stabilize near ambient
• Pile continues slow decomposition
• Immature compounds break down
• Material becomes stable and safe to use

Skipping or shortening curing is one of the most common mistakes. Immature compost can harm plants.

Quality Testing

Before using compost, test for:

• C:N ratio (finished compost should be 15:1 to 20:1)
• Maturity (germination test, CO2 respiration)
• Nutrient content
• pH and EC
• Contaminants if accepting off-farm materials

Equipment Needs

Equipment requirements depend on scale and approach.

Small-Scale (Under 1,000 tons/year)

• Existing farm tractor
• Bucket loader or front-end loader
• Thermometer
• Basic water source

Medium-Scale (1,000-5,000 tons/year)

• Dedicated loader
• Windrow turner (can start with attachment-type)
• Grinder/chipper for woody materials
• Screening equipment for finished product
• Stormwater containment

Large-Scale (Over 5,000 tons/year)

• Self-propelled windrow turner
• Commercial grinder
• Trommel screen
• Dedicated receiving and mixing equipment
• Sophisticated water management

We can help you right-size equipment for your operation—no point buying capacity you won't use.

Common Problems and Solutions

Odors

Cause: Usually anaerobic conditions from insufficient oxygen or too-wet material

Solutions:

• Increase turning frequency
• Improve pile porosity with bulking agents
• Manage moisture more carefully
• Adjust feedstock mix

Slow Decomposition

Cause: Wrong C:N ratio, insufficient moisture, poor aeration, or cold temperatures

Solutions:

• Adjust feedstock ratios
• Check and correct moisture
• Turn more frequently
• Consider covering piles in winter

Incomplete Breakdown

Cause: Woody or resistant materials, insufficient time, inadequate particle size

Solutions:

• Pre-grind woody materials
• Extend composting and curing time
• Screen finished product to remove large pieces

Making Compost Work for Your Farm

Good compost is just the starting point. Applying it effectively requires understanding your soil needs.

Application Rates

Rates depend on crop, soil condition, and compost analysis. Typical ranges:

• Maintenance: 2-4 tons/acre
• Soil building: 4-8 tons/acre
• Problem soils: Up to 10+ tons/acre initially

Too much at once can create nutrient imbalances. We recommend soil testing before major applications.

Timing

For annual crops, apply before planting and incorporate. For perennials, surface apply in late fall or early spring.

Integration with Fertility Program

Compost is a soil conditioner first, fertilizer second. It provides slow-release nutrients but rarely enough to meet full crop needs. Most programs combine compost with targeted fertilizer applications based on testing.

Get Expert Help

Composting isn't complicated, but doing it right—efficiently, legally, and with consistent quality—takes some expertise.

Agconnect's compost consulting service helps you:

• Evaluate feasibility for your operation
• Navigate regulatory requirements
• Design facility layout
• Select appropriate equipment
• Establish operating procedures
• Train staff
• Test and improve product quality

Contact us at 805-467-2233 or [email protected] to discuss starting a composting operation on your farm.

Composting is one component of building healthy soil. Learn more about our approach in our article on understanding soil health, or explore our full range of soil health services.