How to Mix Your Own Soil for Container Plantings

By Bill Marken, Suzanne DeJohn, and The Editors of the National Gardening Association

To make your own planting mix for container gardening, buy a wholesale mixture of a general peat-based growing mix and then customize it to meet your needs.

For example, you can save money by purchasing a large bale of compressed seed-starting mix at the beginning of the season. Use as much as you need to start seeds; then, when it’s time to grow plants in larger pots, mix in some sterilized compost (or composted manure or composted bark mulch) to add nutrients and lighten the mix. If you’re growing trees and shrubs in containers, mix in some builder’s sand or purchased topsoil for added weight.

You can also add fertilizers to a mix. Slow-release formulas, such as Osmocote, that break down and release nutrients when they’re exposed to water are a common choice. Organic options include kelp, alfalfa, and fish meals, which break down slowly, releasing their nutrients to plant roots.

If you add garden soil to your potting mixture, you run the risk of introducing disease-causing organisms to your container mixture. For best results, use only bagged, commercial topsoil, not the backyard garden fare.

With a little knowledge of what to look for, you can’t really go wrong with buying a commercial mix. If you can’t find a growing mix that suits your needs, however, and you really want to get down and dirty, you can mix your own blend. If you decide to take this route, be aware that you may need to experiment to achieve just the right mix.

Here’s a recipe that creates one cubic yard of mix. A cubic yard is a pile measuring 3 feet x 3 feet x 3 feet. That’s a lot of mix! You can make a smaller amount as long as you maintain the proportions.

First combine the following:

1/2 cubic yard of sphagnum peat moss
1/2 cubic yard of vermiculite

Dump the ingredients in a pile on a smooth, clean surface like a concrete patio or driveway, or on a plastic tarp where you won’t contaminate the mix (for smaller proportions, use a wheelbarrow or garden cart). Break up the peat moss as needed so it isn’t clumped. Mix, adding warm water as necessary to lightly moisten the material, and continue mixing until thoroughly combined.

Now add: