I get asked this question a lot…! When filling raised plant beds do you use topsoil or garden soil? There's a big price difference! Oh, and don't forget potting soil, compost, seed starting soil, mulch, and so many more. Where do we start!?
Dirt and soil, while used interchangeably, are not the same thing. Dirt is comprised of sand, silt, and clay, but contains no living matter. Soil, on the other hand, contains the same elements as dirt, but has added minerals, nutrients, living matter and their waste byproducts, air and water. When you start thinking of planting a garden, whether it's in containers, raised beds, or directly in ground, good soil is a REQUIREMENT for success.
Let's take a look at the different types of soil that can be purchased at big box stores or by the truck load from a local nursery.
Topsoil is just as it sounds, the uppermost layer of soil that has been scraped away from some location. Since that location can vary, so can the quality of the soil. I would be hesitant to put topsoil in a garden bed, but it would do fine to fill in holes in the lawn. Garden soil has been mixed to include peat or vermiculite, compost, and most likely a little topsoil. This allows for better aeration and drainage in the bed. You can make your own by buying those three components or you can buy garden soil.
Amending soil before and/or after a growing season can be accomplished in a variety of ways, but primarily, the addition of compost is most beneficial in most areas for most soils. Having said that, getting your soil tested and knowing what kind of soil you have will reduce the amount of frustration you might experience when planting perennials as well as a vegetable garden. Different plants flourish in different soil types and nutrient availability. Knowing what you have and how to amend is an important first step BEFORE you purchase plants.
Sending soil samples through your local county extension office is, by far, the best way of assessing your soil needs. They will report, not only on the type of soil you are working with, but the relative nutrient and mineral content as well. You can do a quick and dirty (pun intended) test at home to familiarize yourself with your most basic soil structure.
I prefer to have my samples sit overnight, just to make sure everything has a chance to settle. You'll notice different layers in your jar, like the cartoon below.
Now it's time to use the soil texture triangle to determine the type of soil you are working with. Don't become overwhelmed! Using this tool is pretty simple. Let's walk through a few examples.
First you want to determine how much sand, silt, and clay you have present in your sample. Look at your container and estimate the percentage for each and then take a quick look at the soil texture triangle. Along the outside of the triangle are the relative percentages of sand, silt, and clay.
You will trace the percentage lines for all three of these texture types (sand, silt, and clay) and where the three lines intersect, the triangle will indicate what type of soil you have present (i.e. sandy clay, loam, silt loam, etc.).
Let's try an example and see if we can get the same answer. Look at the picture on the left and the jar that claims to be LOAM. From the experiment, they claim to have 40% sand, 40% silt, and 20% clay. You know you're doing well when your first check is 40+40+20 = 100% !
--Ok, now, let's start with sand. On the bottom of the triangle, find the 40% sand line (looks to be in the olive green area).
--Next, find the 40% silt line along the right side of the triangle (where the yellow and green-ish colors meet).
--Follow the two 40% lines into the triangle until they meet. To double check, it should cross with another line (clay = 20%). The name of the soil type where all three of those lines cross is LOAM! Congrats! You've successfully used the soil texture diagram. Do another example from the picture on the left to see if your answer matches their soil type.
Now you are ready to try this on your own soil type. Calculate the approximate percentages of sand, silt, and clay in your sample and use the soil texture triangle to determine the type of soil you are working with! Now that you are armed with the knowledge of your soil texture, you are ready to start amending or planting, whichever your plants require!
Before I close this blog, I wanted to briefly touch on the topic of mulch and how it differs from soil. Mulch can be organic (made up of once living things) or inorganic (i.e. rocks) and the type and amount utilized will depend on where it's going in the garden as well as its intended use. We'll have another blog just on the considerations of mulch at a later time, but I wanted to stress that mulch is used ON TOP of the soil to help insulate it, reduce the amount of weeds (reduce, not eliminate), and help retain moisture. Shredded leaves, shredded bark, pea gravel, river stones, etc. are all examples of mulch and each have their pluses and minuses. I prefer organic mulch in my garden/flower beds because as it breaks down over time, it releases nutrients that the plants can utilize. A down side to organic mulch is that it really needs to be replenished on a yearly basis. Inorganic mulches are great around landscape plantings (i.e. bushes) or walkways and while they'll eventually need to be replaces, that typically isn't as frequent as organic mulches. We'll talk much more in depth about all this in another blog.