A brief saunter down the gardening aisle of your local store will quickly reveal there are many soil options out there, all vying for your attention. Where to begin?
“Soils are complex and very much alive and crucial to the success of a garden,” says Paul Zammit, director of horticulture at the Toronto Botanical Garden. After earning a degree in agricultural science from the University of Guelph, Zammit spent 20 years working at a garden center, so he knows a thing or two thousand about gardening.
Zammit says the first question you should ask yourself is: “Where will the soil be used?” What you need for gardening in the ground is very different from what you need for gardening in containers.
Gardening in the Ground
Look for: topsoil or blend
If you want to grow your garden in the ground, buy topsoil or a blend. “If you’re going to mend a lawn or do seeding, and you want something heavier, topsoil or top dresser helps,” Zammit says. “A blend is good for new or existing vegetable and flower beds.”
Blends often include topsoil and may be labeled as “triple mix,” “three-in-one,” or “four-in-one.” A quality blend should contain a combination of loam, peat base, humus, and some form of compost; if you don’t see these keywords listed, it’s a red flag suggesting lower quality.
Blends tend to be more expensive than topsoil because they contain multiple elements.
If you’re gardening in the ground, Zammit stresses the importance of adding organic matter. Why? Because feeding your soil will, in turn, feed your plants. “Worms and other organisms are constantly moving and aerating the soil,” he says. “Organic matter becomes a food source for the worms, the bacteria, and the fungi, and they will release nutrients that the plants can then take.”
To do this, you can add your own compost or buy bags of compost. When shopping for organic matter, look for keywords such as seaweed, manure, mushroom, bone mill, soybean mill, fish meal, worm — whatever’s local and available.
Should I use fertilizer?
Fertilizer is meant to help promote plant growth by improving the fertility of soil but adding too much can harm soil organisms and alter the soil pH. “Soil is alive, very much alive,” says Zammit. “We need to feed the soil and encourage the life of the soil.” Adding organic matter helps to feed the organisms that do all this great work.
Consider Getting Your Soil pH Tested First
Before you even begin planning what you want to grow, consider getting your soil tested. “The pH of your soil will influence how successfully plants will grow, and what plants will grow,” Zammit says. Since pH is very difficult to alter, he recommends working with the soil you have and selecting the right plants for your soil type and soil pH.
(Don't know about pH? Look no further than pH pHacts)
Gardening in Containers
Look for: Container mix
If you’re gardening in a container, Zammit recommends buying a potting mix, which tends to be peat- or chor-based. He advises against using actual soil in a container as it’s too heavy. “It would likely settle and the plants would suffer,” he says, pointing out soil life is very different in a container compared to in the ground.
Watch out for polymers, though; they can reduce the need to water as often but Zammit tends to avoid these because they’re synthetic. Instead, he recommends container mixes that include mycorrhiza: “It’s a soil-born fungi that helps create a relationship with the plant, and they are being shown to be very beneficial.”
(Learn more about container gardening with The Do's and Don’ts of Container Gardening)
Should I use fertilizer?
If you’re gardening in a container, adding fertilizer is a good idea. “Gardening in the ground is about feeding the soil and letting the soil organisms make the nutrients available to the plants,” Zammit says. “With container gardening, because we water more frequently, we often leach out the nutrients in the pots, so we need to supplement with a fertilizer to feed the plants.”
Consider a slow-release fertilizer, which some container mixes may already include. “Slow-release fertilizer helps to get plants established and continue to grow throughout the season,” Zammit explains. “They release nutrients to the plant slowly over time over the growing season based on temperature and based on moisture.”
Whether you’re growing edibles or non-edibles in the ground or in a container, it’s important to recognize the role of your soil. Choosing the right soil will literally help you create a solid foundation for your dream garden.