catalyzing chlorophyll, and dividing cells. The Big Three may be the stars, but they can’t perform at their best without the support of trace minerals.
pH
Your soil will likely be acidic or alkaline, and soil pH measures the degree of that acidity or alkalinity. On the acid side of the soil spectrum (about 4.5), plants such as camellias, blueberries, azaleas, and hydrangeas thrive. In fact, the more acidic your soil is, the bluer your hydrangeas. On the alkaline side (about 8.0), artichokes, mint, and asparagus do well. Most vegetables like to grow in an environment that borders a neutral pH, which is 7.0, with many varieties flourishing in a range between 5.5 and 7.5.
Changing the pH of your soil is not like changing the pH of your swimming pool. In a pool or spa, you just add a few chemicals, and—poof!—the pH is different. It doesn’t work that way with soil. It can take years to alter the pH of your garden soil, so the best approach is to find plants that do well in your existing soil conditions. That said, we’ll cover ways to amend your soil to increase acidity or alkalinity later in this chapter.
Soil Texture
It’s time for a very important question: When you stick a shovel in the ground, does it slide right in, or does it barely penetrate the soil? Your soil’s texture is going to determine how hard you will have to work to get your garden ready for planting, or at least which type of planter bed you will use. With texture, there is also a spectrum, just as with the acid/alkaline spectrum, and your soil texture will fall somewhere along the spectrum between clay, silt, and sand. There are pros and cons for each.
Microscopically, clay soil is made up of small particles, with very little airflow between them. Clay soil tends to drain poorly and is difficult to dig. In spring, in places where the ground freezes over, clay soil takes much longer to thaw, drain, and become ready to work than sandy soil. Many gardeners avoid the whole process by building raised beds (turn back to Chapter 2 if you decide you want to do that). The benefit of clay soil is that it holds water and nutrients very well. Gardeners don’t need to add fertilizer as often, nor do they need to water as much, with clay soil, so it isn’t all bad.
Sandy soil, on the other hand, is very loosely put together. Unlike clay soil, which forms into hard clods that are difficult to break up, sandy soil runs through your fingers and doesn’t hold together if you try to form a clump. Under a microscope, you can see that it is made up of large particles. It’s fantastically easy to dig, and it drains very well. The problem is that it drains too well. As a result, sandy soil loses moisture quickly—with all that fantastic drainage, away flows all of your carefully applied nutrients as well. Gardeners with sandy soil have to water more frequently and generally have to stay on top of adding amendments.
Silty soil behaves like a combination of clay and sand. The particles are larger than clay but nowhere near as large as sand. These particles characteristically feel silky, smooth like flour, or some even say greasy. Silty soil has a tendency to become compacted like clay, making drainage and digging difficult. Silt and sand are both made up of weathered rock particles, so they both respond to gravity in the same way—the particles will settle quickly in a water solution.
THE Soil Food Web
In addition to soil nutrients and micronutrients, there is an entire world (or “underworld,” in this case) of insects and microbial life forms in your soil that make the plant world go ’round. It’s called the soil food web, and the fungi, bacteria, protozoa, earthworms, and nematodes all have a purpose—a job to do. They are the stagehands who make the show run flawlessly.
Dr. Elaine Ingham, a soil microbiologist and president of Soil Foodweb, Inc. (soilfoodweb.com), first wrote about and coined the term “soil food web” during her research on soil microbiology in the 1980s and ’90s. Jeff Lowenfels and Wayne Lewis, while tipping their hats to Dr. Ingham, uncover this world in their book, Teaming with Microbes. They deftly explain how plants not only take up nutrients but also “produce chemicals they excrete through their roots.” The excretions or “exudates” are then consumed by fungi and bacteria, which in turn are consumed by protozoa and nematodes, which then excrete waste that is taken back up by the plant as food. How convenient!
Don’t forget the host of arthropods and insects, which burrow and aerate the soil, living and completing their life cycles (naturally or otherwise, i.e., being eaten by birds or other predators). When they die, their bodies go back into the food chain, breaking down into usable organic matter, which is once again consumed by microbes and, eventually, plants. This overlapping series of complicated food chains is the soil food web. It’s fascinating stuff, but why does this matter to you as a gardener?
It matters because when your soil is healthy enough to support this intricate underworld of microbial activity, your garden will be more likely to thrive. Not only that—everything you do in the garden can help or hamper the soil food web. Every box of fertilizer, every shovelful of compost, every bottle of bug spray that is used on your plants affects this underworld. Don’t worry, though, because we’ll give you all the information you need to steward the microbial life in your garden’s soil food web later in this chapter.
Get Tested
The first thing to do, before adding any fertilizers or soil amendments, is to get your soil tested. It takes a little time, and you have to wait for the results, but it’s worth it. There are two kinds of tests available: basic and complete. A basic soil test reveals the nutrient levels of your Big Three. This type of test usually requires that you take a soil sample, mix it with water, and let it settle. Then you draw off some of the liquid and add it to a beaker with specific chemicals that are reactive to nitrogen, phosphorus, or potassium (this is the fun science part). Close the container, shake it, and then leave it undisturbed and wait for the color to change. You’ll compare your results against a color chart to let you know how well supplied your soil is with that particular nutrient. You can buy basic soil tests for N, P, K, and pH at many nurseries or order them online through gardening catalogs.
Home soil-testing kits test levels of nitrogen, phosphorus, and potassium as well as pH.
The second type of soil test yields more elaborate results. A complete test involves sending a soil sample out to a laboratory. Soil technicians provide you not only with N, P, K, and pH ratings but also with ratings for trace elements, salinity, and heavy metals.
Why is this important? Well, let’s say you live in a city, near a busy road. Your test might show high levels of zinc in the soil. Where did that zinc come from? Zinc disperses from braking systems on vehicles, from roads, from airplanes overhead, and from galvanized metal gardening tools (like watering cans or buckets). Excessive zinc prevents the uptake of nutrients in plants. That’s right—it actually blocks the plant’s ability to extract N, P, and K from the soil. A soil test might also show that the pH of your excessively zinc-laden soil is acidic. This would tell you that, if you were to raise your soil’s pH, you would bind up the zinc, making more nutrients available to your plants.
It’s always a good idea to get a complete soil test to rule out the presence of lead (residues from turn-of-the-century oil drilling, leaded gasoline, and house paints), arsenic (used previously for years near railroads as a weed killer), mercury, cadmium, or aluminum. Most university departments of agriculture offer inexpensive soil tests (just search the Internet for “university soil test” to find one near you), or you can send a sample to a soil lab, such as Wallace Laboratories (wlabs.com) in El Segundo, California. To find
