We’re back with another installment of our Science Series!
This time, we’re investigating soil, and trying to get to the bottom of some of the questions we get a lot at the shop: what makes certain kinds of soil more sustainable than others? Which types of soil are best for certain types of plants? Should we use different soil blends for raised beds and other garden styles?
What you’re looking for
I’ll start with some basics on what’s out there, plus what I usually opt for. Bagged soil can have a lot of manure from large chicken or cow farms; this can end up making the soil too high in saline, so I try to avoid the big brands and choose something a bit more expensive and locally made. I always like to read the bag for tips, and follow the recommended uses for that particular soil.
But what’s in there?
Soil is made up of a mix of minerals, organic matter, water, and air. Types of soil refer to percentages of clay, sand, silt, and loam—which is often what you read about on seed and plant packages. You can actually have way too much compost, as healthy soil only needs about five percent "humus,” defined as the organic component of soil formed by the decomposition of leaves and other plant material by soil microorganisms.
How do you know it’s healthy?
The number of worms in your outside dirt is a good indication of the health of a soil. There's also the pH balance of soil to consider, either alkaline or acidic. It's very difficult to change the pH of soil—there’s a belief that adding coffee grounds will do the trick, and that’s not necessarily so—but you can have your soil tested in Colorado by CSU. This is a relatively easy process that involves ordering the test tube and taking samples from multiple places around the yard, and sending it back in; some soil can be contaminated so it's a smart idea to find out what you're really working with. You can also look up some simple at home tests to get a sense for soil type and pH, although they’re not as accurate as an official test would be.
Types and usage
Soil isn’t one-size-fits-all. It varies by region, and property by property. You can create different soil conditions in raised beds, planters, larger garden plots, and pots—and I’ve found this to be pretty essential to maximizing garden health, no matter what kind of space you’re working with. For example, Loamy soil is ideal for many gardens, lawns, and shrubs (think climbers and vegetables); some vegetables like a more alkaline chalky soil; if you have peaty soil, you might have drainage issues, but if you dig channels and fortify with compost, your salad greens and root vegetables will love it. Most veggies, perennial plants, and a host of tree types will like silty soil. Sandy soil is good for seedlings. If you enhance drainage in harder clay soil, summer vegetables, fruit and ornamental trees, and perennials will enjoy the nutrients it can offer. For a really solid and sustainable potting soil, we love Den. Their soil comes from within a 500-mile radius of their headquarters in Northern California, contains sequestered carbon, and is specifically designed to help plants thrive; it includes ingredients like biochar, fir bark, and worm casings, and it’s entirely plastic-free. They also have a succulent-specific mix and a plant superfood.
