Garden Blog

Make Your Own Potting Soil Mix

Creating your own organic potting soil with recipes from Sow True Seed Asheville NC.

Make your own potting soil with recipes from Sow True Seed Asheville NC.

Eliot Coleman in his book The New Organic Grower writes that he believes, ‘It is false economy to stint on the growth of young plants.’  One of his famous tenants is that a healthy, vigorous plant requires no real management because healthy plants resist disease and insect attack.  It is important to find a good mix and manage your young plants well.

Potting Soil Mix Recipes

Recipes for making your own mix abound.  ATTRA (the National Sustainable Agriculture Information Service) has a great publication on Potting Mixes for Certified Organic Production as well as an extensive list of sources in its appendices. Click here for an excellent recipe via Organic Gardening and ATTRA. Many sources discuss sterilized mixes and others do not.  This is your choice.  Sterilization assures that there are no disease or insect pests present in the media.  However, Eliot has used unsterilized media for greater than 20 years with no problem.  His method is clear and specific and relies on a balanced biological approach to creating a healthy mix.

Many organic soil mixes rely heavily on well screened (1/2”) compost that has matured over several years or sometimes worm castings.  In addition, perlite, which lightens the mix and allows air to circulate, is also added.  Use vermiculite to hold water. An overly dry potting soil mix is never good.  Lime is usually added to bring the mix to the perfect pH, about 6 – 6.5.  The final ingredient in many mix recipes is peat moss or coconut coir.

The Problem with Peat Moss

The harvesting of peat has come into question in recent decades even though its use remains widespread.  Peat bogs form peat at a very slow rate (1/4” per year) and the disturbance of the sensitive hydrology in these rare ecosystems inhibits this formation (Chalker-Scott).  In addition peat bogs, while being a very small part of the earth’s total surface area sequester more carbon than any other ecosystem, up to 75% of the total atmospheric carbon load.  Removal of this carbon rich material additionally subjects it to decomposition outside of it’s previously oxygen poor environment.  Due to the damage incurred on peat bogs from harvesting, the subjection of this carbon rich material to decomposition (therefore releasing additional carbon into the atmosphere) and the availability of alternatives, peat is not the best sustainable choice for a potting mix.

The most frequently available alternative is coconut coir which has been shown to be a reasonable substitute for peat moss in soil mixes.  Coir is sold as a ‘dust’ in compressed blocks and can be substituted for peat 1:1.

Always Add Compost!

When mixing your soil mix ingredients be sure to wet down your coir or compost/worm castings if they are dry. Some of these materials get hydrophobic if allowed to dry out too much.  A wetting down period prior to mixing your ingredients will help them blend nicely and absorb water when you are ready to add your seed.

Happy Gardening!

Post & photos by Sow True Seed Blogger Megan Schneider