The Backyard Gardener (Lyons Press, 2017), by Kelly Orzel, is a concentrated guide to sustainable gardening, whether in a backyard or on a large farm. Orzel is a master gardener and horticulturist who shares her academic and farming experience as an author and freelance writer. The following excerpt focuses on nitty-gritty of soil.
It’s important to have a clean start (sort of). Healthy soil is the most important part of gardening. It costs much less to do it right the first time than if you cheap out and buy bargain brand soil. Not only will you wind up with unremarkable — even poor — produce, you’ll only have to spend more money and resources in the long run.
I think of my soil as a living thing — something to be nurtured, fed, and cared for. Lots of microorganisms play various roles in developing your soil’s structure, aerating it, and mobilizing nutrients. Therefore, you need to know what’s going on under your feet before you can plant.
Not all soils are created equal. Loam is the gardener’s best friend: it contains the perfect balance of sand, silt, and clay particles, along with organic matter. This translates into good drainage, as well as nutrient and water retention, which creates the ideal environment for most plants. Other soil types like clay, sand, silt, and chalk are more difficult and often require more attention to keep your garden healthy. Clay soil is the most fertile since its wet, sticky structure holds nutrients and water tightly. Unfortunately, clay leaves little room for air and water movement, which can lead to root rot. In addition, clay also reacts to temperature extremes: cold, wet soil in cool weather — and hard, dry soil in warm weather. Sand is the opposite of clay. It drains well — a little too well — and readily loses moisture and nutrients. Cacti and succulents thrive in sandy, often acidic, soils, but most other plants will suffer from the lack of water and nutrients. The main benefit to sandy soil is that it warms more quickly in the spring, which is good for germination. Silt falls somewhere between clay and sand, producing light, moist soil that drains well, but also compacts easily. Chalky soil is often shallow, overlays rock, and is more alkaline due to its high lime and calcium carbonate content. The classic ball test will help you figure out what type of soil you’re working with. If you grab a handful of soil and it falls apart the minute you release, you have sandy soil. If it stays compact in a ball, you have clay soil, and if it’s more crumbly, you have desirable loam.
There are some things you can do to improve your soil structure. Adding leaf mold, decomposed manure, and compost to sandy soils will prevent them from draining too much. Conversely, incorporating ample amounts of bulky organic matter or gravel to clay will improve drainage. Unfortunately, you don’t have a lot of options when it comes to chalky soils. My advice: embrace what you have and grow arid, alkaline-loving plants.
The next step is to run a soil test to find out your soil’s pH, its organic matter content, and what its fertility demands are (you can get your soil tested for a small fee through your local cooperative extension office). Think of pH as your soil’s temperature; every species has its own optimal temperature and soil is no different. The pH scale runs from acidic to alkaline, 0.0-14.0, with 7.0 being neutral. A soil pH of 6.5 (5.5-7.5) is optimal for most vegetables. Once you know what you’re dealing with, it’s simple to adjust. Raising pH is a lot easier than lowering it; just add limestone in the fall or winter. Lime is available in multiple forms (fine dust, granular, pelletized, or hydrated) and should cover the area completely — and, if possible, be worked into the soil. It should be spread at least two to three months before you plant since it takes time and moisture to neutralize the acidity. The finer the lime, the more quickly it will work. To lower the pH of highly alkaline soil (most common in arid regions), work aluminum sulfate or sulfur into soil. Aluminum sulfate works faster, but if you have several months before planting time, sulfur will work just as well.
Depending on how you amend and rotate you garden, you may also need to add organic matter to help your soil hold moisture and nutrients better. Your soil test will tell you more about your organic matter and fertility needs, but we’ll talk more about that later.
To dig or not to dig? Unless I’m creating a brand-new garden bed or working with severely compacted clay soil, I do not dig or till. There is a method to my madness, and it has to do with soil structure. Healthy soil is full of earthworms and other soil microbes that naturally till and incorporate your compost into the garden. When I top my beds off with compost, I don’t bother mixing it in. As counterintuitive as it may seem, undug soil will reward you with good drainage, more air space, higher moisture retention, fewer weeds, and stronger, better anchored vegetables. To sum it up: compost feeds soil; tilling destroys it. The microbes that live in the soil, like bacteria and fungi, help mobilize nutrients and extend plant roots to access these minerals, which encourages plant growth. Earthworms are nature’s rototiller, pulling compost and other organic matter deep down into the soil so that fungi and bacteria can break it down and release nutrients. Furthermore, their castings help bind soil aggregates, or groups of soil particles, creating space for roots to grow and air to penetrate. So every time you dig or till the soil, you’re killing these organisms by breaking them up or exposing them to the environment. Tilling makes it more difficult for plants to root, metabolize nutrients, access air, and hold water and brings new weeds to the surface.
Most gardeners don’t realize the importance of air in soil, but it’s vital. Soil aggregates, organic matter, and plant roots create air tunnels and hold them in place. Worms help perforate the soil with a network of channels for air, water, nutrients, and roots to move. Again, with every dig or till, these channels deteriorate, and depending on the extent of the damage, it can take years before they’re reestablished. It’s easy for the untrained eye to mistake firm, undisturbed, healthy soil for the compacted kind, tricking the most well-intentioned gardeners into rototilling. After rototilling, the soil appears “fluffy,” and people think this is the same thing as having well-drained, open soil — it isn’t. So unless you’re reinvigorating a long-forgotten garden or beginning a new one, don’t dig. Also, you may hear or read about a method called “double-digging.” Don’t get excited — this is the same as rototilling. Instead, apply organic matter and compost to encourage microbial activity and build soil structure.