Manure

Manure: What Makes It Fertile?

Everyone knows manure is animal excrement. But what many don’t know is why some types work better than others in the garden.

Why Bird Manure Is the Gold Standard

Bird manure is excellent because it’s rich in urea—an organic nitrogen source and the key ingredient in Miracle-Gro. Birds excrete and urinate through the same opening, and their metabolism naturally produces high urea levels. That nitrogen boost ends up directly in their droppings.

Other Manures: The Good, the Meh, and the Worm Food

• Pig manure gets great reviews, though I’m not exactly sure why.
• Cow manure is okay—decent, but not amazing.
• Horse manure is nearly useless for most plants but fantastic if you’re raising worms. Worms love the stuff.
• Rabbit manure also delivers a solid dose of urea.

Aside from urea, the main “nutrient” in manure isn’t what you’d expect—it’s bacteria. More specifically, dead bacteria.

The Best Fertilizer I Ever Used

Years ago, my biotech company ran a fermentation process using Bacillus subtilis, a non-pathogenic soil microorganism. We extracted the useful product, but the leftover bacterial mass—basically a slurry of live microbes—was a disposal problem. Dumping large amounts of live bacteria into a sewage system isn’t an option. They consume oxygen and can cause anaerobic conditions, leading to foul-smelling bacterial overgrowth.

So, we left the slurry in a barrel for a month. The bacteria died and began breaking themselves down with their own enzymes. One day, we took a whiff—and it actually smelled sweet. E. coli, the bacteria commonly found in manure, never smells sweet.

We diluted that bacterial soup 1:1000 and poured it into my garden. The results were insane. Within two weeks, everything—grass, flowers, vegetables—exploded in growth and color. It was beyond anything I expected.

Why did it work so well? It turns out that bacteria can synthesize all of their own amino acids and most of their vitamins. These are the same amino acids and vitamins used by plants (and humans). In fact, most commercial vitamins are purified from bacteria—not synthetically made.

Through our experiments, we discovered that plants can absorb amino acids and vitamins directly through their roots. That accidental “bug concentrate” fed both plants and soil microorganisms with pure nutrition. Nothing went to waste. The dead bacteria had essentially digested themselves into peptides and amino acids, which plants and microbes could use immediately.

Manure: Same Principle, Less Efficiency

Manure works similarly but far less efficiently. It contains live bacteria from an animal’s digestive tract. When properly composted, heat kills these bacteria. But raw manure is dangerous—it can be toxic and even deadly.

We’ve all heard about flesh-eating bacteria. The main culprit is a strain of E. coli that releases tissue-killing toxins. Other manure-borne bacteria can be just as harmful. In one local case, a camper cut her finger, got infected with a flesh-eating strain, developed sepsis, and nearly died.

Dead bacteria? Great for the garden. Live bacteria from the GI tract? Always harmful. If you’re using cow manure, ensure it’s well-composted, and always wear gloves when handling it. Better safe than sorry.

A Note on Compost and Bug Juice

Commercially certified compost can’t contain manure. If you plan to make Bug Juice using compost as a starter, check that it’s manure-free. Any surviving manure bacteria can multiply in the mix, and you’ll spread them around your home and garden. Not ideal.