How and Why to Use Soil Amendments

Soil is the heart and soul of a garden; it’s what our plants grow in, it’s what provides nutrition and support to the living things around it. While the type of soil we have often determines—along with weather and climate—what we can grow in our gardens, the good news is that we have a bit more control over what kind of soil we have in our gardens. By making wise use of soil amendments—additives that are mixed into soil to change its character—you can improve your soil as you wish, helping you to better grow the plants you want to grow. How soil amendments work, which soil amendments are right for you, and what amendments your soil needs are all big questions, but we’ll do our best to help you find the answers. Let’s dig in!

When to Use Soil Amendments

As we touch on a bit above, soil amendments are best use judiciously when you need to improve your soil due to a particular problem or issue. These problems might include amending dense clay, helping soil drain more effectively, or adding much needed nutrition to your soil. As such, the first step in determining what soil amendment you need is a soil test. Many county extension offices in the US and Canada will do soil test for home gardens at no cost, and there are home testing tools to let you determine your soil’s moisture content, pH, and nutritional content. So: start with a soil test before you start adding amendments to your soil!

A Guide to Soil Amendments

So, now that we know how to get started, which soil amendments are available and what do they do for my soil? While there are dozens if not hundreds of soil amendments out there, in this blog we’ll focus on some of the most common and most useful for home gardeners:

• Compostis perhaps the most commonly used soil amendment, and for good reason! It can lighten the density of your soil, provide nutrients and organic content, and can address drainage issues. Compost is also widely available commercially and can be easily produced at home if you have a little space. Compost works well for any soil that is short on organic matter including clay, sandy soils, and silty/loose soils that need additional structure. However, compost can be used as a fertilizer in most soils, making it perhaps the most useful and versatile soil amendment.
• Wood chips, wood bark, or sawdustare often used as soil amendments, but they can create some issues. As wood breaks down and degrades, it can absorb nitrogen from the surrounding soil. This in turn robs plants of a vital nutrient, preventing them from growing! So with that said we don’t recommend using wood chips, bark, or sawdust in their “raw” state, but rather after they’ve been composted a bit. And even then they’re likely best used in clay or silty soil that needs to be lightened, or as part of a landscaping project addressing drainage issues.
• Manure is another popular soil amendment. Horse, chicken, and cow manures are most common, and they can add a great deal of organic matter and nutrition to your soil. With the exception of rabbit manure, all manures should be composted to avoid adding too much nitrogen too quickly and burning your plants! (Before you ask: mixing green manure and wood chips/bark/sawdust is a bad idea; the reaction between them robs soil of nitrogen until they compost down). Composted manure may be used in any soil that needs additional organic matter, but it’s especially useful in sandy/silty soil that needs a bit of additional structure.
• Wood ashes can be a great soil amendment if use properly. If you have a wood or wood pellet burning fireplace the ashes can either be added to your compost heap or directly to your soil. Wood ash is a alkalizer, increasing the pH of your soil to make it less acidic and more alkaline. However, some wood ashes can add salt to your soil, which limits plant growth. It’s best to use wood ash sparingly, as needed and after soil testing, or in your compost heap.
• Sand is often recommended as a soil amendment with the goal of loosening or lightening dense soils. However, we really can’t recommend it; sand tends to turn clay soils into something like concrete, which isn’t good for plant root development. Sand as a soil amendment is best used in potted plantsthat need help with drainage, or as a base for succulents and cacti.
• Straw is often overlooked as a soil amendment, which is a shame. It’s affordable and can be quite useful in lightening dense, clay soils. It helps aerate garden soil and improves drainage without the nitrogen issues that come with wood chips or sawdust. Straw can be chopped up fairly easily by running it over a few times with a lawn mower before adding it to soil. So if you have clay in your garden, straw might be the answer you need!

So What Soil Amendment Should I Use?

There are so many more kinds of soil amendments, soil additives, and fertilizers out there, but we hope this helps you understand what some of the more common options are and what they can do for your garden. The right soil amendment for your garden will depend on your soil conditions, your climate, and what you’re trying to grow. Again, we recommend getting your soil tested and perhaps talking to experienced gardeners in your area to figure out the best solution for you. Gardening is a very personal thing—your goals  and your space are unique and you deserve the best advice you can get!

If you have further questions about soil amendments, or tips for using them successfully, get in touch and let us know. Gardzen is all about community and we love hearing from you!