Mixing Your Own Potting Soil

The most cost effective way to have a quantity of potting soil for your use is to make it yourself. The following is information on how to do that.

Soil.  A more appropriate term is soil media because the material being sold as potting soil is actually soilless.  Outdoor soil isn’t suitable for potting plants because it can compact in the pot, causing drainage problems for the plant.   It can contain weed seed, disease organisms, and insects.   What the soil-less media provides is support for the plant by anchoring the roots and a medium for water and food to enter the plant through the roots.  There are many options for potting soil that can be purchased ready mixed.  Pro-Mix is a professional potting mix which is light and fluffy and doesn’t compact easily.  There are also types of soil specifically formulated for orchids, cacti, African violets, and seed starting.   I find it cheaper and just as effective to mix my own. 

Basic mix.   A good basic mix is 3 parts peat moss or coir (coir is great if you can get it bulk…from coconut hulls) and one part perlite. Perlite is the white granular material found in premixed soils. For every one gallon of the mix, add 1 tablespoon of ground limestone. The best would be dolomitic limestone because it also provides magnesium.   Wear a dust mask when mixing and handling the materials because it is quite dusty and is quite  unhealthy to inhale a lot of this material.   Once the lime gets mixed in a little, you can add warm or hot water and continue mixing.  There isn’t a dust issue if the materials are wet and it seems easier to get a good mix if it is moist. Peat moss doesn’t absorb water easily if it hasn’t been treated with chemicals to allow it to.  It will absorb water if the water is warm-hot and you continue mixing the mix.  This basic mix can be used for nearly all plants except cacti, carnivorous plants, orchids, and can be used for African violets but it needs a further ingredient to make it more suitable for them. 

African violet soil. 1 part peat moss, 1 part perlite, 1part vermiculite.  To every one gallon of mix, add 1 tablespoon of lime.

Cacti mix. 1part basic mix, 1 part perlite. Doesn’t need lime because there is enough in the basic mix.

Soil Amendments. These are whatever else you want to add to the potting soil to obtain optimal results. They can provide feeding for a couple of months.  I usually supplement with a liquid feed once a month or so just to give the plants a boost because sometimes the organic amendments don’t break down fast enough to feed the plant during rapid growth. 

Amendment Recipe.   I mix this by the handfuls.   It doesn’t matter what size your hand is just try to keep the same amount for each handful.  Or you can use a scoop etc.

1 part cottonseed or blood meal.

1 part sulpomag (a product sold by that name)

1 part greensand

1 part bone meal

1 part dried worm castings (optional)

1 part compost (optional)

The cottonseed/blood meal provides nitrogen, the sulpomag provides sulfur, potassium, and magnesium, the greensand provides more potassium and iron, the bone meal provides calcium and phosphorous, the dried worm castings add all the nutrients including many of the micro-nutrients required for plant growth, as does the compost.

I add 4-6 tablespoons of this mix to 1 gal of basic soil-less mix.  A couple of tablespoons can be added to planting holes outdoors as well.  I particularly like this mix because it is organic and provides all the nutrients the plant needs and will not burn the plants.  I also like the fact that this is higher in potassium.  Potassium helps the plant to have good disease resistance as well as makes it more tolerant of cooler/cold temperatures…something I like the tomatoes to have.

One note, cottonseed meal will cause harmless mold to grow on the surface of the soil.  It won’t harm the plant but is unsightly.  If you want to use cottonseed meal despite the mold and would like to keep it under control, sprinkle a little cinnamon on the surface of the soil.

It may be difficult for an apartment dweller to have access to a compost pile, but if you do, harvest it and pasteurize it for use with the plants.  Heat the compost to 180 degrees F and keep it there for half an hour.  This can be done in the home oven and checked with a meat thermometer saved for this purpose.

About worm castings, sometimes they can be purchased or they can be “grown” in a bin in the kitchen.  It depends on how squeamish everyone in the house is whether you do this.  I have a bin of red worms that compost all of my kitchen waste (no meat) paper towels, plant clippings, and newspaper.  They take this raw waste and turn it into dark, rich material that is super food for plants.  Worm composting is a topic for a future e-book.

I hope this information has been helpful to you and increases the joy you receive from working with plants.