Using Free Manure as Organic Fertilizer: Aging, Nutrient Values, and Best Practices

Free Manure: A Great Resource—If Handled Correctly

Craigslist listings for free manure (horse, cow, etc.) are legitimate and valuable. But raw manure can burn plants and introduce weed seeds. It must be aged/composted before use.

Composting Guidelines

• University of Illinois: How to Compost and Use Horse Manure
• USDA NRCS: Animal Manure Management

Don’t rush—proper aging eliminates pathogens, weed seeds, and excess ammonia/salts.

Typical NPK of Aged Manures (approx.)

Source	N-P-K
Horse	7-3-6
Duck	6-14-5
Chicken	11-8-5
Rabbit	24-14-6
Cow	6-2-5

Values vary by animal diet, bedding, and aging method. Composted manure releases nutrients slowly, enhancing soil microbiology—unlike raw manure or synthetic fertilizers, which can harm microbes.

Nitrogen Forms Matter

• Nitrate (NO₃⁻) – preferred by annuals, vegetables, turf.
• Ammonium (NH₄⁺) – preferred by perennials, shrubs, trees.

Manure-based compost tends toward nitrate; fungal-dominated compost (less manure) suits woody plants.

Caution for Vegetable Gardens

Even aged manure may carry pathogens. Many authorities advise against using manure on edible crops. Consider plant-based compost for food beds.

Bottom Line

Free manure is a fantastic soil builder—if you compost it thoroughly. Test your soil, match the amendment to your plants, and enjoy the long-term benefits of organic matter.