Feedstocks & Recipes

Everything a compost pile consumes. Characterize your materials, then combine them to hit the three targets: C:N of 25:1–40:1, moisture of 50–60%, and enough porosity to breathe.

Browns and greens: the mental model

Browns are carbon-rich, usually dry, woody, or strawy: straw, wood chips, sawdust, dead leaves, corn stalks. Greens are nitrogen-rich and usually moist and green or fresh: manure, grass clippings, food scraps, fresh legume hay, coffee grounds. Browns build structure and energy; greens drive microbial growth and heat. A good pile is built in layers or blended batches of both.

Careful Color is a hint, not a definition. Fresh green weeds can be low-N greens; old straw is a brown. What matters is measured (or table-estimated) C:N and moisture, not appearance.

Typical properties of common feedstocks

Why watch it: a university lecture on the components and requirements of producing compost — what each feedstock contributes, and why particle size and moisture decide as much of the outcome as the C:N ratio does. Useful before you trust any single ratio number. Watch on YouTube ↗

Diagram: logarithmic carbon to nitrogen axis ranging from 10 to 1 up to 400 to 1, with brewery grain, poultry litter, dairy slurry, food scraps, solid dairy manure, horse manure with bedding, autumn leaves, straw, wood chips and sawdust plotted. The 25 to 1 through 40 to 1 band is highlighted as the ideal initial mix. — **Where each feedstock lands.** The green band is the target for an initial mix, not a requirement for any single material — you hit it by blending a green with a brown. Note how far apart the manures and the woody browns sit: that distance is why recipes are ratios, not single ingredients.

Values are representative ranges from published analyses; always analyze your own materials when precision matters (lab C:N + moisture costs little and prevents expensive mistakes).

Material	C:N ratio	Moisture %	Bulk density kg/m³	Notes
Dairy manure (liquid/slurry)	12–20	85–92	950–1000	Needs large volume of dry bulking agent
Dairy manure (solid/bedded pack)	20–30	65–78	500–750	Often composts as-is with minor amendments
Beef feedlot manure	15–20	55–75	600–800	Dense, gravel contamination common
Poultry litter (broiler)	10–15	25–40	400–550	N-rich; ammonia loss risk, mix carefully
Swine manure (solid)	13–19	65–80	800–950	Odorous; strong recipe control needed
Horse manure + bedding	25–40	45–65	250–400	Persistent herbicide risk (aminopyralid)
Straw (wheat/oat)	60–100	8–15	60–120	Excellent bulking agent, slow
Corn stover	50–100	10–20	80–150	Tough; grind or shred for speed
Wood chips	100–500	15–45	250–450	Gold standard for ASP/aeration
Sawdust	200–750	20–60	200–400	Compacts; blend with coarser material
Autumn leaves	40–80	30–45	100–250	Shred to prevent matting
Grass clippings	12–25	65–82	~400	Matts when pure; blend into layers <15 cm
Food scraps	14–20	70–85	~700–1000	Odor/vector risk; mix 2–3:1 with browns
Fruit/vegetable culls	12–25	75–90	~700	Acidic; lime or extra browns may help
Spent brewery grain	8–12	70–80	~950	Excellent N source, easily anaerobic
Coffee grounds	17–25	~55–65	~400	Compact but reliable green
Alfalfa hay	13–20	10–20	100–200	Fast green, weed seeds possible
Biochar (10% v/v)	—	—	~200–400	Additive: N retention, CEC, structure
Gypsum / zeolite / rock dust	—	—	—	Additives: see Additives & Inoculants
Rock dust / lime	—	—	—	Additive only; see pH note

Manures: the farm's core feedstock

For most livestock farms, manure is the reason to compost and the feedstock that defines the recipe. Its characteristics vary enormously with species, bedding, and handling.

Dairy & beef

Solid or bedded-pack dairy manure with straw/sawdust bedding often has usable C:N and moisture straight from the barn, and composts well in turned windrows. Slurry/liquid manure must be dewatered, adsorbed onto dry solids, or blended with large volumes of bulking agent (commonly 1:1 to 1:3 manure:bulking by volume). Feedlot manure is drier and denser but often contaminated with soil and gravel — plan for screening.

Poultry

Litter is the most nitrogen-dense common feedstock (also high in P, Ca, and uric acid). Its uric acid converts to ammonia quickly, so poultry litter piles can lose large N fractions and emit strong odor early. Best practice: blend with high-C browns to an initial C:N near 30–35:1, keep moisture ≤55%, and avoid over-turning during the first two weeks.

Swine

Swine manure is wet, dense, and notoriously odorous; it composts best after solid-liquid separation or with generous bedding (deep-bedded systems produce excellent compostable material). Covered or aerated systems are strongly preferred.

Horse stables

Bedded horse manure is a convenient, well-balanced farm feedstock — with one critical caveat: some pasture herbicides (aminopyralid, clopyralid, aminocyclopyrachlor) pass through the animal and persist in hay/bedding and remain herbicidally active in finished compost, damaging tomatoes, beans, and other sensitive crops. Verify herbicide history before accepting off-farm stall waste.

Persistent herbicides Before composting hay, bedding, or stall waste of unknown origin, run a bioassay: germinate peas or tomatoes in a mix of compost + potting soil and watch for cupped leaves, twisted growth, and poor root development over 2–3 weeks.

Crop residues and other on-farm materials

Straw & stover: high-C browns and structural backbone of many farm recipes. Shredding accelerates use.
Spoiled silage: usable but variable; blend and monitor pH/odor.
Culls & packout: wet, fast, acidic; blend with ample browns to prevent anaerobic pockets.
Mortality (on-farm): legal in many regions via dedicated static-pile mortality composting — heavy cover (2 ft finished compost), core at 55 °C+, and strict biosecurity separation. Check local rules; the full method is in Mortality & Specialty Waste Composting.
Manure solids from separators: fibrous, moderately dry; excellent base feedstock.
Wood ash: adds K, Ca, raises pH; use sparingly (≤5–10% by volume) and never with lime-sensitive crops in mind.
Biochar: pre-charged with nutrients ("charged" by soaking in manure slurry) to avoid temporary N tie-up in the pile.

Bulking agents and structure

A pile needs porosity as much as it needs nutrition. The bulking agent provides persistent air channels; without it, wet feedstocks collapse into anaerobic sludge. Particle size guidance: fine (<2 mm) decomposes fast but compacts; coarse (2–5 cm) sustains airflow for weeks; larger than ~6 cm may need screening out and recycling.

Wood chips are the classic choice for aerated systems because they persist through the active phase and can be screened out and reused 3–5+ times, amortizing their cost. Straw decomposes within the cycle (contributing nutrients) but offers less durable structure. A practical starting mix for wet feedstocks is 1 part feedstock to 1–2 parts bulking agent by volume, tuned by moisture and squeeze test.

Interactive C:N mix calculator

Enter up to six ingredients with their C:N, moisture, and mass (any consistent unit — kg, lb, tons). The calculator computes the blend's combined C:N, moisture, and guidance flags.

Ingredient

C:N

Moisture %

Mass (kg or lb)

— : 1

Blended C:N ratio (dry mass basis)

Add ingredients to begin.

Estimated blend moisture: —%

Assumptions The calculator uses the standard approximation that ~50% of dry matter is carbon (so C:N alone drives the mix, without needing separate %C and %N inputs). It is a planning tool — verify the built pile with a thermometer and squeeze test, and refine with lab data for repeated recipes.

Interactive moisture adjustment calculator

The other half of the recipe: your pile (or blend) is at X% moisture and you need it at Y%. Enter the current mass and moisture, pick a target, and choose whether you're adding water or a dry amendment. It solves the dry-matter balance for the amount to add — and shows what the addition does to your C:N.

Current pile mass

Current moisture %

Target moisture %

Add

Amendment moisture %

Pile C:N (optional)

Amendment C:N (optional)

—

Amount to add (same units as the pile mass)

New total mass: — · Final moisture: —%

Blended C:N after addition: —

Enter values to begin.

Assumptions & limits Dry matter is conserved; only water moves. Moisture percentages here are wet-weight (water ÷ total mass), the same basis as the squeeze test. If the chosen amendment is wetter than the target — or you're adding water to dry down — the tool tells you instead of giving a nonsense number. For large corrections, make them at turning, in layers, not by dumping onto the surface.

Pair it with the C:N mix calculator: that tool plans the recipe from scratch; this one corrects a pile or blend that's already built. Both are planning aids — the squeeze test and a thermometer at the pile remain the ground truth (see moisture management).

Other feedstock considerations

Food scraps & off-farm organics

Food scraps are nitrogen-rich and very wet; they bring revenue or fees in some markets but require excellent odor and vector management. Covered aerated systems or immediate heavy blending with browns are near-mandatory at any real scale. Contamination (plastic, glass) is the dominant operational headache.

Biosolids

Municipal biosolids compost into a valuable product and are legal for many uses, but are prohibited in certified-organic production (NOP) and carry PFAS scrutiny in many regions. Check both your intended market and state rules before sourcing.

Yard trimmings

Municipal leaves, brush, and grass are often available at low or negative cost (gate fees) and make excellent browns — but confirm herbicide history and screen for contaminants.

What never to compost (or only with care)

A short but critical list — the difference between a kitchen-garden pile and a commercial facility is partly what you refuse:

Material	Risk	Practical rule
Diseased plant material (clubroot, some wilts, viruses)	Plant pathogens may survive normal heating	Exclude or dedicate a far-off static mortality-style pile; research crop-specific survival before relying on heat
Treated lumber, painted wood, MDF, ash from pressure-treated wood	Arsenic/copper preservatives, glues	Never — toxin concentration into crop product
Coal ash, chemical containers, batteries, sharps	Metals, residues, injury	Never
Dog/cat/other carnivore feces	Zoonotic parasites (Toxocara, Toxoplasma)	Exclude from any food-crop compost
Persistent-herbicide residues (aminopyralid-clopyralid hay/bedding)	Survive composting, injure sensitive crops	Bioassay; refuse unknown hay/bedding sources (see manures)
Plastic-laden food waste, coated paper	Microplastics into soil	Screen incoming; document contaminant policy
Weed seed-heads of noxious species	Distribution via product	Hot-process or screen; know your weeds
Oils, fats at scale, dairy-dense waste	Anaerobic pockets, strong odor, vectors	Small quantities only, well mixed into hot piles; large flows need dedicated systems

The refusal is the product Every off-farm feedstock you accept exports your reputation into someone else's waste stream. A written acceptance policy — what you take, what you refuse, how you document — is the cheapest quality-control instrument you own.

Accepting off-farm materials: a due-diligence toolkit

Gate fees are tempting and most on-farm operations cross this line eventually. Before you do:

Legal check first: accepting off-farm feedstocks usually shifts you out of the small-farm exemption into permitting territory (see the regulatory map) — resolve this before the first truck.
Know your offtake: an extra feedstock doubles your product volume; have land, storage, or market before you take it.
Contamination policy: inspect every load; refuse visibly contaminated material at the gate; charge clean-up fees for hidden contaminants.
Document: load manifests (source, date, description, weight), batch records, and end-use logs — your traceability story starts at the gate.
Bioassay unknowns: for hay/bedding/fiber sources, run the pea-tomato bioassay (see persistent herbicides) before large-scale acceptance.
Food-waste logistics: covered receiving, immediate blending with browns, vector control, and leachate handling (see water).

Key takeaway Characterize before you commit: know each material's C:N, moisture, and contamination risk. A 30-minute recipe calculation prevents weeks of odor, slow piles, and lost nitrogen — and a written intake policy protects the product you sell.