Composting

Part of Fertilizers & Soil Amendments

Composting transforms organic waste into rich, stable humus that feeds soil biology and provides slow-release nutrients to crops. It is the single most important soil-building technique available without industrial chemistry — and it costs nothing but labor and time.

Why Composting Is Foundational

In a rebuilding scenario, synthetic fertilizers do not exist. Every nutrient that leaves the soil in a harvested crop must be returned somehow, or yields will decline year after year until the land is barren. Composting closes this nutrient loop by converting kitchen scraps, crop residues, animal manure, and weeds back into plant-available nutrition.

Beyond nutrients, compost improves soil structure — it helps sandy soil retain water and helps clay soil drain. It feeds the billions of soil organisms that make nutrients available to plant roots. No other single technique does as much for long-term soil fertility.

The Science of Decomposition

Composting is managed decomposition by microorganisms — primarily bacteria and fungi. These organisms consume organic matter, breaking complex carbon compounds into simpler ones and releasing nutrients in plant-available forms.

What Microbes Need

Requirement	Why	How to Provide
Carbon (C)	Energy source	Brown materials: dry leaves, straw, sawdust, cardboard
Nitrogen (N)	Protein for growth	Green materials: fresh plant matter, manure, food scraps
Water	Medium for biochemical reactions	Maintain 50-60% moisture (damp sponge feel)
Oxygen	Aerobic microbes work fastest	Turn pile, use coarse materials for air gaps

The C:N Ratio

The single most important composting concept. Microbes need roughly 25-30 parts carbon for every 1 part nitrogen (by weight) for optimal decomposition.

Material	C:N Ratio	Category
Fresh grass clippings	15:1	Green (nitrogen-rich)
Food scraps (vegetable)	15-20:1	Green
Fresh manure (chicken)	7:1	Green
Fresh manure (cow/horse)	20-25:1	Green-brown border
Dry leaves	50-80:1	Brown (carbon-rich)
Straw	75-100:1	Brown
Sawdust	200-500:1	Brown (use sparingly)
Cardboard/paper	200-400:1	Brown
Wood chips	400-700:1	Brown (very slow to decompose)

The simplest rule: mix roughly equal volumes of green and brown materials. This approximates a 25-30:1 C:N ratio without any calculations. If the pile smells of ammonia, add more brown. If it is not heating up, add more green.

Building a Compost Pile

Site Selection

• Well-drained ground — standing water creates anaerobic (smelly, slow) conditions
• Partial shade — full sun dries the pile too quickly in hot climates
• Near the garden and kitchen — convenience increases usage
• Downwind from living areas — even well-managed piles have some odor during turning

Pile Dimensions

The minimum size for effective hot composting is roughly 1 cubic meter (1 m x 1 m x 1 m). Below this volume, the pile cannot retain enough heat. Maximum practical size is about 1.5 m tall — taller piles compact under their own weight and restrict airflow.

Layering Method

Build the pile in alternating layers:

1. Base layer — coarse sticks and branches (10 cm) for drainage and airflow
2. Brown layer — 10-15 cm of dry leaves, straw, or shredded cardboard
3. Green layer — 5-10 cm of fresh plant matter, food scraps, or manure
4. Thin soil layer — 1-2 cm of garden soil (inoculates with native microbes)
5. Water — sprinkle each layer until damp but not dripping
6. Repeat layers until the pile reaches 1-1.5 m tall
7. Cap with a brown layer to reduce odor and flies

Containment Options

Type	Materials	Advantages	Disadvantages
Free-standing pile	Nothing needed	Simplest, no construction	Looks messy, animals access easily
Wire mesh bin	Wire fencing + stakes	Easy turning, good airflow	Does not retain heat well
Pallet bin	4 wooden pallets	Free materials, easy to build	Gaps let material fall out
Brick/block bin	Bricks, blocks, stone	Permanent, neat, retains heat	Labor to build, hard to turn
Three-bin system	Any of above x 3	Best workflow — fill, cook, cure	Most space and materials

Hot Composting vs. Cold Composting

Hot Composting

Active management produces finished compost in 4-8 weeks. The pile heats to 55-70°C, killing weed seeds and pathogens.

Requirements:

• Correct C:N ratio (25-30:1)
• Adequate moisture (50-60%)
• Sufficient volume (1+ cubic meter)
• Regular turning (every 3-5 days)

Temperature progression:

1. Mesophilic phase (days 1-3): bacteria activate, temperature rises to 40°C
2. Thermophilic phase (days 3-21): heat-loving bacteria take over, 55-70°C
3. Cooling phase (days 21-35): temperature drops, fungi and actinomycetes colonize
4. Curing phase (days 35-56): stabilization, humus formation, earthworms arrive

Maintain the thermophilic phase (above 55°C) for at least 3 consecutive days to kill weed seeds and most pathogens. If the pile never gets hot, the C:N ratio is wrong — add more nitrogen materials.

Cold Composting

Passive composting — just pile materials and wait. Takes 6-12 months or longer. Does not kill weed seeds or pathogens, but requires almost zero labor.

Best for: low-labor situations, materials that arrive gradually rather than in large batches.

Turning and Aeration

Turning introduces oxygen, redistributes moisture, and moves outer (cooler) material to the center (hotter zone).

When to Turn

• First turn — when internal temperature peaks and begins to drop (usually day 5-7)
• Subsequent turns — every 3-5 days during the thermophilic phase
• Later turns — weekly during cooling and curing phases
• Stop turning when the pile no longer reheats after being turned

How to Turn

Move the outside of the pile to a new location (or the adjacent bin in a three-bin system), placing it in the center. The old center goes to the outside. Water any dry material as you go.

Temperature Monitoring

Without a thermometer, use the hand test:

• Insert your hand into the pile center (wearing a glove)
• Hot but bearable — roughly 50-55°C, good
• Too hot to hold for 5 seconds — above 60°C, excellent
• Barely warm — below 40°C, needs more nitrogen or moisture or is finished

A length of rebar or metal pipe driven into the center of the pile and left for 10 minutes makes a crude thermometer. Pull it out — if the exposed section is too hot to hold comfortably, the pile is above 55°C.

What to Compost (and What Not To)

Good for the Compost Pile

• Vegetable and fruit scraps
• Eggshells (crush first)
• Coffee grounds and tea leaves
• Grass clippings (thin layers — they mat)
• Dry leaves
• Straw and hay
• Livestock manure (cow, horse, chicken, goat, rabbit)
• Crop residues (corn stalks, bean vines, etc.)
• Weeds (before seed set, or in hot piles only)
• Wood ash (sparingly — raises pH)

Avoid or Use Caution

• Meat, bones, dairy — attract rodents and bears; compost only in well-managed hot piles
• Diseased plants — only if pile reaches 60°C+ for several days
• Dog and cat feces — may contain parasites; avoid for food garden compost
• Treated wood, coal ash — contain toxins
• Large branches — take years to decompose unless chipped first

Knowing When Compost Is Ready

Finished compost should be:

• Dark brown to black in color
• Earthy-smelling — like forest floor, not sour or ammonia-like
• Crumbly texture — no recognizable original materials
• Room temperature — no longer generating heat
• Populated with earthworms — if available in your area

Unfinished compost applied to gardens can rob nitrogen from soil as microbes continue decomposition, harming crops. If in doubt, let it cure another month. Finished compost improves over time, but immature compost causes problems.

Common Mistakes

1. Too wet — soggy piles go anaerobic, producing methane and hydrogen sulfide (rotten egg smell). Add dry brown materials and turn immediately.
2. Too dry — decomposition stalls completely. The pile should feel like a wrung-out sponge. Water during construction and after turning.
3. All green, no brown — produces a slimy, smelly, nitrogen-rich mess. Balance with at least equal volume of carbon materials.
4. Pile too small — volumes under 0.5 cubic meters cannot self-insulate and will not hot-compost. Make bigger piles or insulate with straw bales.
5. Never turning — even cold compost benefits from occasional turning. For hot composting, turning is essential to maintain oxygen levels and redistribute heat.

Summary

Composting — At a Glance

• Composting closes the nutrient loop — returning organic waste to the soil as plant-available fertility
• The C:N ratio (25-30:1) is the key variable: mix roughly equal volumes of green and brown materials
• Hot composting (55-70°C) finishes in 4-8 weeks and kills weed seeds and pathogens
• Minimum pile size: 1 cubic meter for effective heat retention
• Turn every 3-5 days during the hot phase; monitor temperature by hand or rebar method
• Finished compost is dark, crumbly, earthy-smelling, and no longer heats up
• Never apply immature compost to crops — it robs nitrogen from the soil