How To Test Garden Soil
Gardeners often disregard the impact soil has on the health and vigor of their plants. Soil preparation isn’t the most thrilling aspect of planting a garden, but it’s certainly one of the most important. If your soil isn’t right, your garden will struggle to reach its full potential.
Start by digging up a scoop of soil and examining its texture in your hands. Photo by: Sharon Kingston / Shutterstock
“A garden is a reflection of the quality of its soil. Gardens filled with beautiful soil have a vitality about them that we can almost feel,” says landscape designer and author Jan Johnsen.
Achieving that vitality requires understanding the chemistry and composition of your soil and creating the perfect environment for fertile plant growth. Good soil management is a continual process, but once you attend to the basics, your soil will do most of the work itself.
6 Basics of Healthy Soil
1. Know Your Soil Type
Before you begin planting, dig up a scoop of soil and take a look at its texture. Is it dense and heavy and clump together when wet? Or is it loose and free flowing, like play sand? Maybe it’s somewhere in between, feeling somewhat sticky but crumbling easily, like a freshly baked cookie.
All soils are a mixture of mineral particles — primarily clay, sand, and silt. Often they will contain higher amounts of one type of particle relative to the others. That doesn’t make them bad growing mediums, but it will affect their density, drainage rate, and capacity to hold nutrients.
With each soil type, there are trade-offs. Here’s a quick overview:
- Clay soils have tiny, dense particles that hold large reserves of moisture and nutrients. However, clay soil also drains slowly and can become hard and compacted when dry.
- Sandy soils are just the opposite, with large particles that water moves through easily — along with important nutrients.
- Silts have fine particle sizes that pack together tightly, inhibiting drainage and air circulation.
- Loam is the ideal soil for most plants; it contains a balance of all three mineral particles and is rich in humus (what’s left after organic matter decomposes).
If you have poor soil, consider building a raised garden bed and filling it with a well-balanced soil mix. Photo by: Jan Johnsen.
Adding organic matter is the best way to make your soil more loam-like and improve its structure. Another option is to build a raised garden bed and fill it with a well-balanced soil mix. Or take the simple approach by growing plants that do well in your soil type, such as choosing drought-tolerant plants for sandy soils. You can grow a garden successfully in any soil, as long as the plant’s roots are accustomed to the conditions.
2. Test the pH of Your Soil
The pH of your soil is one of the most important factors in determining its fertility. If your soil is too alkaline (with a pH above 7.5) or to acidic (with a pH below 5.5), that can make a big difference in which nutrients are available to your plants.
Although most plants will tolerate a wide range of pH levels, they prefer slightly acidic soils (with a pH of 6 to 7) because important nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium dissolve readily in that environment. In soils that are too acidic or alkaline, your plants may get too much of some nutrients and not enough of others.
When testing the pH of your soil, take samples from different sites in your garden because the pH can vary even within a small backyard. Photo by: Jan Johnsen.
How do you test your soil pH? Here are two options:
- DIY Soil Test Kit: For the quickest results, you can buy an instant-read soil test kit or electronic tester (such as this one from Amazon).
- Professional Soil Analysis: But if you’re starting a new garden, it’s a good idea to have your soil tested professionally. The soil samples will be sent to a lab, which will analyze your soil pH and nutrient content as well as its capacity to retain nutrients. Try the Soil Savvy Test Kit, also available on Amazon.
Be sure to take soil samples from different sites in your garden because the pH can vary quite a bit, even within a small backyard. If your pH reading is low (acidic), you can correct it by adding lime to your soil. If it’s too high, add powdered sulfur or aluminum sulfate. Another option is to choose plants that will thrive at the natural pH level of your soil, such as acid-loving rhododendrons or azaleas.
3. Amend with Organic Matter
Any type of soil can be improved by the addition of organic matter.
Here are three common amendments:
- Composted yard waste
- Fallen leaves
In sandy soils, organic matter improves water-holding capacity and the retention of nutrients. In clay soils, it loosens up the minerals that become sticky when the soil is wet and hard when the soil is dry. And in all soils, it provides a rich supply of slow-release nutrients for your plants as well as food for beneficial soil organisms. Over time, a well-amended soil will provide most of the nutrients your plants need, reducing fertilizer requirements.
Most soil amendments work best if you work them into the soil in the fall, so they are well decomposed before planting the following spring. Photo by: Jan Johnsen.
Most soil amendments work best if you work them into the soil in the fall, so they are well decomposed before planting the following spring, explains organic gardener Elizabeth Stell, author of Secrets to Great Soil. To get the organic matter down to root level, use a garden fork to mix the material into the top 4 to 6 inches of soil. In vegetable gardens, which usually contain annual or biennial plants, you can amend your soil each season. Perennial gardens should be amended prior to planting so you won’t disturb the plant roots. Many perennials must be dug up every few years for division, providing a good opportunity to work in additional organic matter.
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