Let’s celebrate the earth—by planting a garden. But wait! Good gardening begins right at ground level, with the soil. Let’s take care of that first.
Native plants vary in what kind of soil suits them best, but in turns out that most garden plants, although hailing from all corners of the world, have surprisingly similar soil requirements. Simply put, garden plants need soils that are well-supplied with air (yes, roots must breathe!), water, and nutrients.
And one other important ingredient, humus, that witch’s brew of organic materials that, in addition to contributing to the just-mentioned needs, also supports a friendly microbial community in the soil for optimum plant health. Organic materials are things that are or were once living; they put the “organic” in organic farming and gardening.
Aeration must be the first consideration because most edible plants can’t utilize nutrients, even in fertile soils, if their roots are gasping for air. Waterlogged soil is the result either of a high water table, with water coming up from below, or because a soil has pores so small that they cling by capillary action to too much water.
For a site with a high water table, either choose another site for planting, raise roots above the water table, or lower the water table. Growing plants in raised beds is one way to bring the roots above the water table. Build beds sufficiently high to take the roots up out of the water, and sufficiently wide so they don’t dry out too quickly. To instead lower a water level, drain water away to lower ground by digging trenches or by burying perforated, plastic pipe.
Small pores clogged with water is a common condition of clay soils. Clay particles are small, and thus have small pores between them. Aerate such soils by “gluing” the small clay particles together into larger units, which creates larger pores in the soil that hold air rather than capillary water. (Small pores within each large aggregate will hold water for plants.) The “glue” that holds the small clay particles together is that humus, previously mentioned, and the source of that humus is organic materials such as compost, peat moss, manure, leaves, wood chips, and sawdust. Mix an abundance of any or all these materials into the soil.
Sandy soils represent the opposite extreme from clay soils. With mostly large pores, sands hold plenty of air but can’t hold moisture. Trudging water all season long to plants is one cure. A more practical approach is, once again, humus. Mix an abundance of organic materials into such soils or lay them on top as mulch. In this case, the sponge-like nature of decomposing organic matter holds moisture in the soil.
With aeration and water taken care of, consider your soil’s fertility. Soils must supply plants with more than a dozen essential nutrients, and in order for a plant to utilize those nutrients, the soil’s acidity also must be in the correct range.
Most cultivated plants thrive best in slightly acidic (pH 6 to 7) soils. Determine your soil’s acidity either with a purchased kit or by taking a soil sample to the Cornell Cooperative Extension office in Kingston. Make your soil more acidic with sulfur, less acidic with ground limestone; both are mined natural materials. The amounts needed to change acidity depend on how much of a change is needed and how much clay is in the soil. To change a soil one pH unit requires, per ten square feet, two-tenths to one pound of limestone or one-tenth to one pound of sulfur. The lower values apply to sandy soils and the higher values apply to clay soils.
Periodic fertilization is needed to replace nutrients that wash out of the soil or that you carry away with your harvest. Mostly, plants need nitrogen, phosphorus, and potassium, and these might be the only nutrients you need to add deliberately, the others hitchhiking along with all those organic materials you added to the soil. Nitrogen is the nutrient needed in the greatest quantity, especially for heavy feeders such as vegetables. Less hungry plants, such as many flowers, especially wild-ish ones like coneflower and liatris, thrive with nothing more than mulch of some organic material.
You can, of course, buy fertilizer to supply nitrogen and/or other nutrients. Much simpler, though, would be to lay down an inch depth of compost every year. That amount of compost provides all the nutrition needed, as well as nourishing soil life. And good quality compost, which can be purchased in bulk or made at home, is the most earth-friendly way to nourish your garden.
Lee Reich, PhD is a garden and orchard consultant; he also hosts workshops at his New Paltz farmden (inquire at leereich.com/workshops).