What You Need to Know About Using Topsoil to Make Your Garden Thrive
No matter where you garden, it's worth improving the quality of the topsoil you've got. After all, plants rely on topsoil, the uppermost layer of the earth's surface, for water and necessary nutrients. The more organic matter it has, the darker the soil will look (like what you may see sold in bags or bulk as "black dirt"). This type of soil is very easy to dig in and support healthy plant growth. However, the type of soil in your yard may look very different. Depending on your region, it can vary from reddish clay to beige sandy soil. Here's what you need to know about improving your topsoil.
Topsoil Myths & Misunderstandings
These four common assumptions about topsoil can trip you up. But knowing these basics will help you successfully create the best environment you can for your plants.
Topsoil Myth 1: All Topsoil Is Pretty Much the Same
Topsoil can differ dramatically, even in the same yard and from one garden bed to another. All the earth in your yard is made up of sand, silt, and clay in various amounts. The best ratios of these three elements allow for good drainage yet hold enough moisture for roots. Your soil can also vary in pH, which is a measure of how acidic or alkaline it is; some plants such as bigleaf hydrangeas are more affected than others by this soil quality.
Topsoil Myth 2: The Dirt in My Yard Is Fine the Way It Is
If you recently moved into a home that was previously owned by a skilled gardener, then maybe this is true. But more often than not, the quality of soil around homes, especially newly constructed ones, isn't the best for plants. It takes time to build up high-quality soil that includes generous amounts of decomposed plants, called organic matter. This is a vital component that gives topsoil good drainage, just the right water-holding capacity, and a loose, easy-to-dig quality. It's also important for supporting a healthy soil ecosystem of microbes that help plants grow better.
The quickest way to great garden soil is to purchase it. You can put a 2-3 inch thick layer directly on top of existing soil before planting and just let nature do the rest of the work, or you can till it in. On top of that, you can amend your topsoil further with a couple of inches of compost. This can be a lot of labor, but ultimately it creates very productive soil.
Topsoil Myth 3: To Always Have Good Topsoil, I Have to Till It Annually
If you're creating a new garden space, and want to till in soil amendments to get everything off to a good start, that's fine. But after that, it's best to avoid disturbing the soil as much as possible. For one thing, turning soil can stimulate weed seeds to sprout, so you'll just be creating more work for yourself to get rid of them. And for another, nature will take care of mixing in organic matter so you really can save yourself the trouble.
Tilling may be necessary if your soil becomes very compacted, which means it doesn't have enough tiny air pockets in it that roots require. You can avoid this by staying off your soil, especially when it's wet. If you need to walk into a bed to care for plants, you can minimize compacting the soil by creating a permanent stepping stone path you can use for maintenance or temporarily laying down a sheet of plywood while you work.
Topsoil Myth 4: Rich Soil Never Needs Fertilizer
Plants draw the nutrients they need to grow from the soil. Those nutrients usually need to be replenished every so often for the healthiest growth, no matter which type of soil you have. This is especially true for the soil where you grow annual flowers and vegetables, which suck up a lot of nutrients to fuel their rapid growth. Luckily, it's easy and inexpensive to restore nutrition by adding high-quality compost and/or granular or liquid fertilizer products as needed. If you're not sure if you need to add nutrients, a soil test is a quick way to check. To add nutrients and to replace organic matter as it breaks down, add 1-2 inches of compost to your garden beds in the fall. Then you'll be all set for spring and can just add a layer of mulch after cleaning up and planting your beds for the new growing season.
Common Topsoil Questions
Once you've decided to add topsoil to your garden, now what? Time to think about how you want to use it, where to get it, and how much you need.
What can I use topsoil for?
Topsoil is a good choice for filling up raised beds, repairing eroded spots, or filling in holes. When planting a new lawn or overseeding a patchy lawn, you can use a thin layer of topsoil to protect grass seeds as they sprout. One thing you shouldn't use topsoil for is filling your containers. It won't drain as well as you need it to in a container, and it makes your pots very heavy. Stick with potting mix ($7, The Home Depot) for containers, and use topsoil in garden beds.
Where can I Buy topsoil?
Topsoil is widely available through a variety of sources, including garden centers, nurseries, and home improvement stores. Topsoil is sold by the bag ($3, Lowe's) totaling a cubic foot, or in bulk, which is usually priced by the cubic yard (the price varies based on location and availability). Usually, commercially available topsoil has been screened; this means any extra materials such as small rocks, roots, and debris have been removed.
How do I figure out how much topsoil I need?
If you need to fill a raised bed or install a berm, measure the area's square footage and depth to estimate how many cubic feet of topsoil you'll need. To spread over a garden bed, you’ll want enough to give you at least a 2-inch layer. To install a new lawn, plan to spread a layer of 3-6 inches of topsoil before sowing seed or laying sod, depending on the quality of your existing soil.