What’s In Potting Soil? Everything But Soil
By: Alia Hoyt
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If you find it shocking that there’s no actual dirt in potting soil (also known as potting mix), you’re not alone. Much of the confusion is probably because gardening experts don’t use the word “soil” the same way that regular people do. “Soil is a broad term and is often used interchangeably with planting medium. Soil in general is composed of minerals and organic matter (decomposing plant, animal or microbial matter),” explains Paul Cunningham, hard goods buyer for Pike Nurseries
Potting soil usually contains a combination of Canadian sphagnum peat moss, composted or aged bark, compost, earthworm castings, horticultural grade perlite, pumice or cinders and controlled-release fertilizer, according to Cunningham. “Single-ingredient items like peat moss or bark are not technically soil because they do not contain the full mix; however, they can be used as planting mediums for potted plants,” he says.
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University of Maryland Extension. By comparison, “Topsoil placed in a container stays wet and restricts air movement. The more shallow the container the bigger the negative effect,” he says.
Potting soil also needs to be lightweight to keep shipping costs down and protect the backs of avid gardeners, says horticulturist and gardening expert Melinda Myers. “Eliminating soil from the mix reduces the risk of soil borne and based insect and disease problems,” she adds.
But thrifty gardeners looking to save a few bucks should never forego potting mix for readily available dirt. “Do not dig up the soil from your garden and place it in a pot. It will not drain well (even if it is well-drained garden soil) when confined to the small space of a container,” Myers says via email.
So when should you use potting soil? “We generally recommend potting soil for any indoor or outdoor container gardening – glazed pots, hanging baskets, window boxes and even raised beds,” Cunningham explains. “Your local garden center can confirm which potting soil is the best planting medium based on plant selection.”
Many die-hard gardeners opt to make their own potting mix from scratch. Check out this YouTube video to learn how.
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What’s In Potting Soil? Everything But Soil
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