Soil from the ground is the most common reason a container garden fails before it starts. What you fill the pot with matters more than the pot, and it is the one place not to save money by digging in the yard.
Why not garden soil
- It is too dense. In a pot it compacts, and air and water stop moving through it.
- It weighs roughly 75 pounds per cubic foot, against about 10 for a soilless potting mix.
- It can bring insects, weed seeds and disease with it.
What to buy
Buy a bagged potting mix made for containers. These mixes contain no soil at all. Typical ingredients are peat moss or coconut coir, composted bark, perlite (the white specks, for drainage), vermiculite (holds water and nutrients) and sometimes compost, plus a little lime and fertilizer.
- Names on bags vary a great deal, and so does quality. Look for “potting mix” or “container mix” and a light, fluffy feel. Leave “topsoil” and “garden soil” on the shelf.
- If the bag says it feeds plants for a number of months, fertilizer is already mixed in. Do not add more until that runs out.
- As a guide, one 2-cubic-foot bag fills three 5-gallon buckets.
Two things not to do
- No gravel in the bottom. A layer of gravel does not improve drainage; water collects in the mix just above it. Use rocks only if you need weight to stop a pot tipping.
- Do not pack the mix down. Fill to about an inch below the rim so there is room to water.
Can you reuse it next year?
Extension services disagree. Maryland says to mix last year’s mix half and half with fresh mix or compost. NC State and Illinois say it can be reused if no soil-borne disease was present. Colorado State and Texas A&M say never to reuse it. A reasonable reading: if your plants were healthy, refresh the old mix with at least as much new mix; if anything died of rot or disease, throw that pot’s mix away.
Sources
Every fact in this guide comes from the publications below. None of them reviewed or endorsed Balcony Bounty.
- University of Maryland Extension. Growing Media (Potting Soil) for Containers. extension.umd.edu/resource/growing-media-potting-soil-containers
- Purdue Extension. HO-200-W: Container and Raised Bed Gardening. extension.illinois.edu/sites/default/files/container_raised_bed_garden…
- University of Illinois Extension. Container Gardens: Soil. extension.illinois.edu/container-gardens/soil
- Rutgers New Jersey Agricultural Experiment Station. FS1215: Outdoor Container Gardening with Flowering and Foliage Plants. njaes.rutgers.edu/fs1215/
- University of Maryland Extension. Growing Vegetables in Containers and Salad Tables. extension.umd.edu/resource/growing-vegetables-containers-and-salad-tab…
- NC State Extension. Extension Gardener Handbook, chapter 18: Plants Grown in Containers. content.ces.ncsu.edu/extension-gardener-handbook/18-plants-grown-in-co…
- University of Illinois Extension. Container Gardens: Container Drainage Options. extension.illinois.edu/container-gardens/container-drainage-options
- University of Maryland Extension. Types of Containers for Growing Vegetables. extension.umd.edu/resource/types-containers-growing-vegetables
- Colorado State University Extension. Container Gardens. extension.colostate.edu/resource/container-gardens/
- Texas A&M AgriLife Extension. E-545: Vegetable Gardening in Containers. aggie-horticulture.tamu.edu/wp-content/uploads/sites/12/2011/03/E-545_…
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