Garden Soil Basics

A healthy garden begins with healthy soil. In addition to providing physical support to the plant, soil plays a role in gas exchange, water retention and filtration, as well as temperature moderation. It also holds important minerals that provide nutrients to the plant, and many macro and microorganisms live in the soil that help plants thrive.

Soil Types

Soil types range from sand to clay, and the soil that falls somewhere in the middle between these extremes is known as silt or loam. Soil type determines what plant varieties will grow best, and can provide clues to how to successfully manage your garden. For example, sand is a very large particle, and makes soil porous, which means water moves very quickly through the soil. While this helps prevent flooding after a heavy rain, it also means a gardener may need to water plants more often as water travels out of plants’ root zones too quickly for plants to adequately absorb all of the moisture they need. On the other hand, clay soils are composed of very small particles and therefore has small pores, which generally means that drainage is poor. Small pores also provide less space for air in the soil, which makes these soils more prone to compaction.

Diagnosing Soil Health Problems

If many of the plants in your garden are suffering and you don’t notice any visible pest or disease problems, soil health may be the issue. The first step in addressing soil health is to collect a soil sample. Connect with your local extension office, which will likely be able to send a sample of your soil to a soil testing lab. The test results will provide information about soil pH and nutrient deficiencies. Most vegetables prefer a pH between 6 and 7, so if your results fall within that range, pH is not the problem. To prepare samples for the lab, dig 6"–12" deep and put a sample of the soil in a clear plastic bag. If you have a larger garden, it’s a good idea to get a few samples from different sections of the garden, which you should put in separate bags and label what areas of the garden each sample comes from. Make sure the soil is air-dry before sealing the bag and sending it to your extension office.

Improving Your Garden Soil

A few key methods can help ensure soil is healthy for many gardening seasons to come. The first is to practice crop rotation. This means that you shouldn’t plant crops from the same family in the same place year after year. For example, eggplants, tomatoes, and peppers are all part of the Solanaceae family, so if you plant eggplant in a corner of your garden this year, next year you should avoid planting eggplant, tomatoes, and peppers in that spot. This helps reduce pest problems, but it also helps cut down on disease occurrences, as some diseases can remain in the soil for several years after being introduced.

In addition to crop rotation, it’s a good idea to plant a cover crop in beds that are not in use. Some cover crops, such as red clover and hairy vetch, are especially good choices as they have high nitrogen content. At the end of the season, they are simply turned under and be incorporated into the soil to provide nutrients for next year’s crops. Cover crops also function as a ground cover – reducing unwanted weeds and helping prevent soil from eroding when it rains.

Adding compost and other organic matter also improves soil health. Adding compost increases available water in the soil, adds nutrients, reduces the need for fertilizer inputs, and helps with disease suppression.

Finally, to help your soil retain water for longer and to suppress weed growth, you can add a layer of mulch in your garden aisles and around plants. Mulch comes in many forms, and some common examples include wood chips, straw, shredded bark, buckwheat hulls, and leaf debris.