My Winter Garden

How I fell in love with horse manure

During the gray days of November, the wind scraping dry leaves across the pavement, I long for my blooming summer garden now asleep under a bed of kitchen compost for the winter. It is this time of year when my thoughts turn to horse manure.

I have a couple of cold frames, plywood boxes topped with scavenged glass doors. The cold frames are the start of my winter garden, but if I were to just drop in seeds and close the lid, sunshine alone would not be warm enough to germinate seeds even for cold weather crops like spinach and arugula. That’s where the horse manure comes in. Manure has magical properties. It breaks down into fertilizer and as it does so, it gives off heat.

In late November, I rent a pickup truck and drive it out of town to the stables of Boston’s mounted police. They generously share with me fresh horse manure. I ask to make sure they don’t spray the stalls with insecticides to kill flies. The same toxins also assasinates healthy soils. I pile in just less than half a truck bed of the manure-straw mix, enough to fill two trenches the size of the door-sized cold frames to a two feet depth.

Once the horse manure is in the trench, I cover it with about four inches of top soil (the fresh manure on its own would burn out plants). I poke in a thermometer and wait for the microbes in the manure to heat up. After about 48 hours the temperature is hot—about 120 degrees. I wait a few days until it falls to about 90 degrees, then I poke in the seeds and close the glass lid. In the moist, self-heating, little greenhouse it takes no more than two days for the seeds to sprout. They grow slowly because the winter light is feeble compared to the fierce sun of spring, but the seedlings do grow.

I don’t do much else. If we have snow, I go out and clear it off to let the light in. I forget about the boxes and sprouts until about early March when I notice the greens are right at the glass, practically pushing the lid off, so impatient they are to burst out of their winter container. That’s when I take out my scissors. March is the new May and we are eating fresh greens again.

I learned how to make hot beds in a book that an English gardener Thomas Smith wrote in 1911 called A quarter acre of French gardens. Smith and others of his generation were intrigued with the urban farms of Paris. In 1900, five-thousand Parisian farmers grew enough fruits and vegetables to feed two million Parisians with a surplus left over to send to London.

I normally don’t think of 19^th-century farmers in big cities, but Parisian farmers were creating a whole new kind of agriculture. They used the newly-emerging megapolis of Paris to grow far more food per acre than farmers in the countryside. They located their farms inside courtyards where brick walls blocked cold winds. They stapled fruit trees and berry bushes against sun-baked walls, and took advantage of warm pipes flowing underground. They built soil from composted trimmings, food scraps and organic industrial wastes such as beer mash and sugar beet pulp. And yes, they piled mountains of horse manure into hot beds to grow spring crops in winter and summer crops in spring. As each crop ripened, Parisian farmers piled on more compost and planted again, raising three to six crops a year in quick succession.

Parisian farmers were engineers, transforming the climate and the calendar to their benefit while inventing the most productive agriculture in recorded human history. And what I love about it is that they did not rely on indentured workers digging out guano for fertilizer in South America. They didn’t leave farm fields exhausted and eroded. They did the reverse. By making good use of the mountains of horse manure from 100,000 Parisian horses and other urban waste, they were cleaning up the city. They even had enough leftover compost to sell to farmers in the countryside who had striped the nutrients from their fields. Their growing plants scrubbed the air of CO2 and served up green spaces for birds, animals, and humans. That is the kind of circular metabolism I’m aiming for, wasting as little as possible. I like to think of those nutrients passing from one body on to another like neighbors handling water in a bucket brigade.