"We know more about the movement of celestial bodies than about the soil underfoot." These words were spoken by Leonard DaVinci, a man who Wikipedia tells us was an "Italian polymath." And yet his polymathy transformed into dumb wonder when thinking about the complicated stuff that is dirt.
Today, we're in pretty much the same spot as DaVinci when thinking about soil. We've learned many things about it since the Renaissance, like that one square inch contains over a billion micro-organisms; yet how these organisms function in the soil is still a matter of speculation. One thing is for sure though: soil is very important. And a beginning gardener should consider the health of her soil before anything else. Fall is an excellent time to do this.
Soil is made up primarily of some combination of sand, silt, and clay, which are represented by the soil triangle
. If you live in Detroit proper, you probably have a heavy clay soil. However, some areas just north of the city, Ferndale for example, are mostly sand. Different soils have their advantages and disadvantages. Sandy soils drain well, but clay soils are better at holding on to nutrients. It's nearly impossible to change the base mineral structure of your soil though, unless you want to build raised beds. What you can change is the percentage of your soil that is made up of organic matter, or OM for short. Many soils in Detroit are only 2 to 3 percent organic matter, whereas an extremely productive prairie soil might be at 10 percent.
Adding OM to your garden can offset problems you might have with your base soil. In short, this is a miracle substance that can solve (almost) all your soil problems. Does your sandy soil drain to quickly? OM will hold on to water and nutrients that might otherwise escape. Does your clay soil hold too much water and become a swamp in spring? OM will soak up this water like a sponge and prevent pooling. Organic matter can also supply most of the important macro- and micro-nutrients that a vegetable or flower garden will need, as well as inoculate the soil with billions of beneficial micro-organisms per square inch. These microbes perform vital functions like protecting plants from disease, retaining water and nutrients, and making nutrients in the soil and organic fertilizers available to plants. This is why organic gardeners say, "Feed the soil, not the plant." Unlike water-soluble synthetic fertilizers like Miracle Grow that feed plants directly and only for a short period of time, organic fertilizers feed the soil microbes that in turn make these nutrients available to plants as they're needed.
Forms of OM
Organic matter comes in a number of forms, including compost, manure, leaves, straw, wood mulch, and more. Compost is probably the best form for direct addition to the soil. It's a well-cured and stabilized source of nutrients and microbes that can be incorporated into the soil to supply most plants needs. Leaf, straw, and wood mulches should be left on top of the soil where they can break down and slowly contribute to the life of the soil. Of these, only leaf and straw mulches are really suitable for direct addition to vegetable beds.
Why do this in fall?
Many people mulch their garden beds in fall to protect the soil from erosion and slowly contribute organic matter. Perennial gardens benefit from a fall addition of wood mulch to protect tender perennials during the cold months. The world provides a number of sources of quality OM at this time of year in the form of leaves, decorative straw bales, spoiled produce from this year's harvest, and yard waste (collection of which stops after Thanksgiving in Detroit).
This is a great time of year to start a compost pile
. The gardener can stockpile leaves to provide the carbon, or "brown," element to her compost pile to use throughout the following year. The aforementioned spoiled produce, including rotting jack o'lanterns and yard waste, provide the "green," or nitrogen-based, material necessary to start or build a serious pile. Together these constitute the basis for a quality compost, which as my friend Patrick Crouch has said is "the engine that drives the Cadillac" that is your organic garden.
Take the test
If you are looking to start a vegetable garden, it's pretty important to get your soil tested for pH, percentage of organic matter, and lead. Fall is a great time to do this because it will give you all winter to evaluate your test results and help you plan your garden. UMass Amherst offers a relatively inexpensive soil test
. The testing procedure involves taking a number of trowel's worth of soil from your current or proposed garden–say 10 to 20–putting these in a bucket and mixing them up. Take a cup of this to composite and put it in a plastic bag and mail it (some people dry it out a bit first by putting it on top of a radiator to save on postage). The pH and percent organic matter will give you a good baseline to begin improving your soil. A pH of 7 or less is ideal, but this can be offset over time with addition of… you guessed it ORGANIC MATTER! A desirable lead level will be less than 300 parts per million. If you're looking to do vegetable gardening and you lead level is higher than this, you may want to consider growing in raised beds. If you have reason to believe that one part of your yard is more contaminated with lead than another–say it is near a house that has likely been painted with lead based paint,–take separate soil samples so that you can more accurately distinguish where might be a safe place to grow.
This is the first piece in a series on urban gardening we're calling "Notes for the Beginning Gardner."
Brian Allnutt is a Detroit-based writer and a co-owner of Detroit Farm and Garden.