Potting Soil Basics
by Pamela Kock

Spring is a great time to re-pot your plants, if they are outgrowing their current homes.  It’s also the right time to take cuttings, make divisions, and re-arrange your plants in creative ways.  Before you do this, you’ll need to choose the perfect potting medium, or soil, for your plants.  There are a lot of different types, so how do you choose the right soil?

Ordinary garden soil should never be used for indoor potted plants, or for any plant grown in a container.  Topsoil is also a poor choice, because it usually contains pests, weed seeds, and diseases, and needs to be sterilized before using indoors.  An ideal potting soil contains different amounts of several basic ingredients, depending on the needs of the plant variety. 

Bark:  comes in different sizes of chips, from small for most potting mixes to large chunks for plants such as orchids that don’t grow in soil.

Compost:  provides nutrients; should be well-aged and sifted thoroughly before use. 

Peat Moss:  holds moisture

Sand:  provides drainage. 

Pumice or Lava Rock:  lightweight material that prevents soil from being compacted.

Perlite:  prevents compacting of soil; holds moisture and air better than lava rock. 

Vermiculite:  a type of mica that holds moisture better than perlite.

You can make your own potting soil by combining these ingredients in the proper ratios for your plants, but most indoor gardeners will find it more economical to simply purchase the correct blend. 

 Most houseplants do well in an all-purpose potting mixture.  All potting mixtures are not created equal, however. 

Basic All-Purpose Mixture:  Contains composted bark, peat moss, and sterilized soil. 

Premium All-Purpose Mixtures:  Usually contain more bark and peat moss and less soil.  They may also contain vermiculite or perlite to aerate the soil, and some contain chemical wetting agents to hold and distribute water more effectively.

Professional Mixtures:  Contain the same ingredients, but are finer in texture.

Some potting soils also contain fertilizer pellets.  These can be convenient to use for most plant varieties, but read the label and keep in mind that after the fertilizer is used up (usually about three to six months after potting) you’ll have to begin feeding the plant yourself.

Special Needs

African Violet mixes, which are also good for other flowering plants such as gloxinias, miniature roses, and others that need to stay evenly moist, contain extra organic matter.

Cacti and succulents need good drainage, as too much moisture can harm or even kill them.  Cactus mixes contain a quantity of sand in addition to the basic potting soil mixture.

Most varieties of orchids do not grow in soil.  Therefore, orchid potting mediums are mostly composed of bark chips, which hold water, nutrients, and give the roots a surface to cling to.  They can also contain lava rock, clay pellets, perlite, sphagnum moss, cork, peat moss, and charcoal.  Choose the mixture most recommended for your type of orchid.

Recipe for an All-Purpose Potting Soil:

 1 part sterile soil

1 part peat moss, compost, leaf mold, or fine bark

1 part sharp sand (washed, coarse, river sand)