Back in the late ’80s, I went to Guatemala on a credit card. I stayed on a farm full of young almond trees owned by a Californian not much older than I was. Over beers one day, he told me he had a cow horn buried in his field. It was filled with manure and would come to enrich his almonds like no fertilizer on earth. I was convinced he was drunk. Or a warlock.

Flash forward a few decades and I now know he was neither. It seems cow horns stuffed with manure are buried on biodynamic farms all over Southwest Colorado (and the world). And the ingredients have a rather non-mystical name: Preparation 500.

While Prep 500 is just one of nine essential elixirs that the father of biodynamics, Rudolf Steiner, developed as part of his holistic approach to agriculture, it often ranks as the most renowned. This is no easy torch to carry when you consider the other preps include processes like stuffing chamomile blossoms in the small intestines of a cow, burying them in autumn, and retrieving them in spring.

“There is definitely a spiritual aspect to it. Some faith and intention,” says Emily Jensen. She and her husband, Mike, own Homegrown Farm, a biodynamic farm in Bayfield, Colorado.

Here is how it works. On the autumn equinox, take a cow horn (a bull horn won’t work), stuff it with fresh manure from a pastured and preferably lactating cow, bury the cow horn approximately 18 inches underground lying on its side with the opening facing down (to prevent rainwater from collecting inside, thus ruining the process). Step away for six months. On the spring equinox, dig up the horn. Inside you will find tangible evidence that a physical transformation has occurred. A once rank and greenish manure is transformed to a brown, springy, dirt-like texture with a sweet earthy smell. But you’re not done. Relatively minuscule amounts of this rich soil become the base of a solution.

“It’s delivered in an envelope” says Jensen, who doesn’t bury cow horns but instead purchases her prep.

Amounts vary slightly. The farmers at Homegrown use about a baseball-sized clump of prep for every six gallons of water. This will treat their entire 2.5-acre farm. The solution requires creating a deep tornado-like vortex through one hour of constant stirring. Throughout the mixing, it is important to interrupt the vortex you have created and stir in the opposite direction. It’s also important to bring intention to what you’re doing. So don’t plan to multi-task.

“It is the cosmic channeler of energy,” Emily says. “I say that with a little bit of irony.” While some biodynamic farmers have automated this process, the Jensens use a bucket and a stick.

It is said that the manure is infused with the energy of the earth. The number 500 comes from the 500 million more micro-organisms present than when you buried the horn – all waiting to go to work.

“You are potentizing it. The shape of the cow horn, the shape of the vortex … the Fibonacci sequence. It brings action to the microbial activity,” Jensen explains.


The resulting solution is immediately applied in a thin layer using a simple backpack sprayer. You can also use a paintbrush. Dip the brush in the bucket and flick it on your soil. These are homeopathic amounts.

There are skeptics. Steiner uses esoteric words  like “cosmic” and “holistic” and “anthroposophical” to explain his theory, language which certainly would send half the farmers in this region into a catatonic state.

“Obviously, I think preps work or I wouldn’t go through the trouble to make them. Because it is quite a bit of trouble,” says Pat Frazier of Peace and Plenty Farm in Hotchkiss, who makes and uses all nine of Steiner’s preps with the help of the community. “The waste of the farm is actually the nutrients of the farm,” she adds. “It is a healthier farm.”

While Frazier (and any other biodynamic farmer) doesn’t recommend using preparation 500 alone, she says it’s better than nothing. “Its function is to promote proliferate growth in the early spring, but at some point you need to give them [the plants] a different message.” That, Frazier says, is when preparation 501 comes into play. It involves crushed quartz crystals. A mystical rung of the biodynamic ladder better left for another story.

“We are growing the soil” Jensen says. “The vortex, the cow horn, is all about quality. That is the point.”