Soil is the basis for everything we do in the garden. It provides our plants with critical elements that they need to thrive: nutrients, water, air, and physical support. If you want a prolific garden and bountiful produce, it starts with the soil. Having some basic knowledge about soil under your belt can help you be the master gardener I know you are!
Consider this your soil Cliff’s Notes. You’ll be better prepared to tend to your soil if you understand what makes it so complex and important to your plants’ survival. These are some soil fundamentals all gardeners should know.
Soil has Structure
Ideally, soil is only about 50% solid material by volume â€“ the rest is pore space, which allows your plants’ roots access to water and gives them room to grow. Like me, you’ve probably grown carrots before that were not the long, slender cylinders you were hoping for, but instead orange shorties. Right? That’s all about pore space and airy soil!
There are two kinds of pores in the soil: macro and micro. Macropores, which are created by earth worms tunneling through your rich soil, allow for the movement of water and provide drainage. Micropores help soil to hold water, which is especially helpful during warm months when it rains less frequently. A well-structured soil is like a sponge, holding water that your plants need through micropores and allowing excess water to drain out through macropores.
Soil is a mixture of particles, which are different sizes:
- sand = coarse, visible to the eye, largest of the three particles, gives the soil a gritty feel
- silt = smaller than sand, about the size of a particle of flour
- clay = the smallest, one particle could be seen under a microscope, usually feel very hard when dry
A loam, which is what makes the ideal garden soil because of its balance of macro and micropores, is a soil with roughly an equal mixture of each of the three types of particles. A good loam holds moisture, but allows for good drainage too! Score!
Soil Levels (Horizons)
Soil structure builds in layers, or horizons. Topsoil is the layer closest to the surface and the lower layers below are called subsoil. The topography and climate of an area majorly influence how soil is formed. Soil structure builds slowly over time.
Most gardeners know that even though it looks like a unliving material, healthy soil is teeming with microorganisms and is very much living. It’s a good thing too because that action in the soil is what makes it possible for your plants to get the nutrients they need to survive. The thing is, nutrients in the soil that plants need are not in a form that are readily available for plants (i.e. in their soluble form) until nutrients that come from the minerals in the soil are weathered or until organic matter in the soil is broken down and those nutrients are released by helpful organisms like bacteria, fungi, and insects.
Caring For Your Precious Soil
So, as you can tell, there is a lot more to healthy soil than meets the eye. Good soil takes time to build and is the cornerstone of a productive garden. Here are three easy ways to take care of it.
Avoid Compaction (A.K.A. Don’t walk on it!)
Compaction destroys the fragile macropores that allow water to circulate and drain out of the soil. Compacted soil also makes it difficult for roots to penetrate the soil, which means they’ll have less access to the nutrients they need and will possibly be stunted in growth (think about those carrots again). You can easily avoid this by not walking on your soil. I’ve intentionally built raised beds that are just wide enough for me to reach into and work. You don’t want to squish those beneficial pores you’ve created in your soil.
Watch Out for Wet Soil
Working the soil when it is wet can damage soil structure, so it’s best to wait until a few dry days to dig. Alternatively, you can lay a tarp over the site where you plan to dig a few days before you do the work. This will both help the soil to dry out a bit and will warm up the soil, which is important for good seed germination. Also, if your soil is really wet or you notice big puddles of water in one area, it might be a sign that there is not adequate drainage in the area. You may need to come up with a plan to divert excess runoff that may be affecting your garden or use raised beds for plants that need well-draining soil, which most do.
Add Organic Matter
It is a sign of healthy soil to see earthworms squirming around in it, not just because they help aerate the soil, but also because they are helping the plants access the nutrients they need by consuming organic material and excreting (we’re talking worm poop here) water-soluble nutrients that are ready for plants to absorb. There’s nothing worms like more than rich organic material, like compost. When organic matter decomposes, it forms humus, which binds and strengthens soil particles. Organic matter for the win!
Soil nutrients, pH and fertilizer are topics for another article, but are equally important soil-related issues to consider when gardening. For more information on these topics or on soil in general, check out this link for an incredibly helpful list of resources!
Reference used for this blog post: Sustainable Gardening: The Oregon-Washington Master Gardener Handbook, October 2008
Soil horizons image from here