What Is a Planting Mix Formula?


Planting mixes or, potting soils, consist of several key ingredients intended to help your plants, whether in your garden or in pots, thrive. The old saying, your garden is only as healthy as your soil, is true. You can make your own planting mix or buy one at your local nursery. Before you go shopping, be certain you know what your soil needs.


Test the health of your garden soil by testing your drainage. Slow drainage is usually a sign that your soil could use amending. Dig a hole 6 inches wide by 1 foot deep. Fill it with water and let it drain completely. Fill it again. If it takes more than four hours to drain the second time, you likely need to amend your soil for drainage problems. For potted plants, garden soil is often too heavy to use. Potting soil needs to be lightweight, able to hold water, but also able to drain well in order to avoid root rot, stunted or withering growth and the spread of diseases and fungus.


Planting mixes are divided into two kinds. Soil mixes contain peat moss, soil, vermiculite and compost. Add peat moss and vermiculite in equal parts to your garden soil prior to planting in the spring. Mix well with compost. If your garden is established, adding compost around the base of plants helps keep the soil moist. Soilless mixes are lightweight and ideal for container gardening. They contain peat moss, vermiculite and sand or fine wood products. The primary goal with potted plants is to keep them moist, but not wet. Nurseries and garden stores will have several varieties of bagged planting mix. Or you can make your own.

Key Ingredient Definitions

Vermiculite is a naturally occurring mineral used in planting mixes to hold and then slowly release water and to keep the soil from compacting. Peat moss, also referred to as sphagnum, is made of a variety of decomposed mosses. Peat moss absorbs air and water and allows your soil to breathe (good for clay soils) and retain moisture (good for sandy soils).


At the beginning of the planting season, apply a slow-release fertilizer with an equal amount of nitrogen, phosphorus and nitrogen (indicated by numbers such as 10-10-10 on the product packaging). Later in the season, to encourage blooming, look for a fertilizer with a higher phosphorus number such as 15-30-15. You can also try organic fertilizers. Bone meal is a good source of phosphorus and is a slow-release fertilizer. Blood meal is an excellent source of nitrogen. Lime is used to adjust the pH of soil by reducing acidity.

Cover Crops

We often don't think much about our gardens in the winter, but the fallow months of the year can be important to your soil's health. Cover crops not only help to prevent soil erosion, but will add important nutrients when you till them in coming spring. More nutrients in the spring means you will have even healthier soil to start your next season.

Keywords: planting mixes, container gardening, vegetable gardening

About this Author

Erika Sanders has been writing since 1997. She teaches writing at the Washington State Reformatory and edits the monthly newsletter for the Collaborative on Health and the Environment, a national nonprofit organization. She received her Master of Fine Arts in fiction from the Solstice MFA Program at Pine Manor College in Boston.