Make Your Own Organic Potting Mix
Commercial potting mixes have a lot going for them: they're convenient, widely available and usually provide a good medium for plants to grow in. What they often aren't, is organic. Many potting mixes contain wetting agents, synthetic starter fertilizer and other non-organic additives. In addition, the few organic potting mixes that have come on the market have usually gotten the thumbs down from growers due to both their cost and their failure to produce healthy plants.
A couple of years ago, I decided that I was getting sick of making my own certified organic potting mix and started looking around for somewhere I could purchase it from. The organic grower's supply company sales representative I spoke with asked me if my mix worked well for me and grew healthy plants. I told him that it did and, to paraphrase his words, he replied "if you have an organic potting mix that actually grows plants reliably and consistently, don't bother shopping around for a better one, just consider yourself lucky!". I still make all of my own potting mix.
Making potting mix is a very simple process that is akin to making cookie dough:
1. Mix a lot of different ingredients together in the correct proportions
2. Clean up the mess!
The only supplies you will need are your ingredients and a container to mix them in and a place to store your finished mix, if you aren't going to use it right away. A trash can or a large storage tote works well for mixing and storing small batches. You can mix the ingredients with a shovel, a big stick or your arm. If you are lucky enough to have a concrete mixer, you can mix all of the ingredients in it and save yourself a lot of stirring!
Most potting mixes are "soil-less" mixes. Soil is heavy and doesn't have the moisture holding capacity or the "fluffiness" that potting mix needs to have. In addition, soil can harbor insect and disease pests that harm your plants. Typically, mixes are composed of ingredients that will hold a lot of water and air used in conjunction with ingredients that will provide nutrients to the plants.
Water and air holding ingredients that can be used in organic potting mix include:
Peat Moss--this widely available ingredient does a great job of holding air and water. Make sure that the peat you use has not been treated with a chemical wetting agent.
Newspaper--Reuse, recycle. Ground up newspaper can be used as a substitute for peat moss. Just don't use glossy paper and don't let the paper make up more than 25% of your mix.
Coir-- this by-product of the coconut industry has some nutrients as well as good water holding capacity.
Perlite--allows for excellent drainage and air circulation
Vermiculite--holds water, air and nutrients
Alfalfa, kenaf, sawdust and non-swelling marine clays (usually imported from Canada) are other potential potting mix ingredients that have good water and air holding capacity.
Organic potting mix ingredients that provide nutrients to your plants include compost, alfalfa meal, cottonseed meal, worm castings, greensand, rock phosphate. A good compost will often contain enough nutrients to get your plants off to a great start. So, a simple way to make your first potting mix is to mix compost, peat moss and perlite or vermiculite together until you get a fluffy mix that is well-drained yet holds plenty of water for your plants.
Making your own organic potting mix can save you money and allow you to grow plants that are larger and healthier than they would have otherwise been. Developing a recipe that grows huge, healthy plants and uses a combination of ingredients that fit with both your budget and your visions of environmental responsibility (i.e. no animal ingredients or no non-local ingredients) is both an art and an adventure.
For More Information:
This fact sheet explains how to develop your own recipe for organic potting mix and how to test your potting mix to ensure that it will set you up for plant-growing success. http://www.uvm.edu/vtvegandberry/factsheets/pottingmix.html
This is thorough and useful publication for folks who are really serious about making their own potting mix. It contains lots of sample recipes and gives good explanations of what typical potting mix ingredients are and where they come from. http://attra.ncat.org/attra-pub/PDF/potmix.pdf.
Tammy Biondi has been growing organic produce for over 10 years. Besides running Blue Horizon Farm, Tammy teaches about sustainable farming at the Central Carolina Community College. She also is a successful freelance writer, focusing on agricultural topics. Contact her at firstname.lastname@example.org.