Mix Your Own Potting Soil for Container Plants

Potting soils contain organic matter to help hold water and nutrients in the soil. A careful look at the components of potting soil reveal the essential ingredients necessary for healthy plant growth and development.

Peat, Perlite and Vermiculite

Peat consists of the partially decomposed remains of bog plants. It is probably the most common ingredient in potting mixes.

Perlite is another component of potting soils. Perlite particles are the solid white volcanic materials that hold water only on the outside, instead of soaking up water like a sponge. Perlite does a great job of improving aeration and drainage of potting soils.

Vermiculite is another ingredient that can be found in some mixes. This mica-like ore can hold a surprising amount of water–up to 16 times its weight! Like perlite, vermiculite also helps improve water drainage in a mix. Vermiculite is a common ingredient found in seed starting mixes because it holds just the right amount of water necessary for seeds to germinate.

Both perlite and vermiculite are lightweight materials. To add weight to potting mix for container plantings, substitute sand for half of the perlite. The sand improves water drainage similar to perlite, and it adds weight to the container, especially important for keeping containers from toppling over in high winds.

Make Your Own Potting Soil Mix

If you plan to fill a lot of containers with plants, you may want to make your own potting soil to keep your garden budget from getting soiled. Here’s a recipe for a soil-less potting mix that was developed at Cornell University. This homemade potting mix is relatively simple to prepare, since it doesn’t contain soil or sand, and you won’t need to perform any heat pasteurization to eliminate disease-causing organisms.

Mix together the following ingredients:

• 1 bushel (8 gallons) shredded sphagnum peat moss
• 1 bushel (8 gallons) perlite or vermiculite
• 1/2 cup ground limestone
• 1/3 cup complete analysis fertilizer, such as 18-9-18, or a balanced slow-release fertilizer, such as Osmocote

Here are some tips to keep in mind:

• Moisten the peat moss the night before you want to use it so that it will easily absorb more water at planting time.
• When adding perlite, wear a face mask to avoid inhaling the dust.
• Do not add too much lime. You need only 1 part lime to 20-40 parts peat.
• Store prepared soil in an airtight container, such as a plastic container with a tight-fitting lid or a covered, metal container. Once the mix is in the container, sprinkle the mix with water to moisten it before storing.

For water-loving plants in hot, dry areas, mix water-absorbent polymers called hydrogels into the potting soil. They can improve the water-holding capacity in the soil and reduce the amount of watering.