Making Your Own Potting Soil

Sphagnum peat moss – this is the primary ingredient in most potting soils. It takes peat a long time to breakdown is widely available and inexpensive.  It will bulk up potting mixes without adding weight and once wet, holds water pretty well. Sphagnum peat moss is well-draining and well-aerated but it is also very low in available nutrients and has an acidic pH ranging between 3.5 to 4.5. Adding limestone to peat-based potting mixes helps balance the pH level.  Plants such as lettuce, Russian sage, and marigolds prefer sweet soil with a pH of 7.5, while other acid lovers, like ferns, asters, and strawberries prefer a pH of 5.5 to 6.0.  Here is a list of more plants’ pH preferences.

Coir fiber – this is a by-product of the coconut industry. It looks and acts like sphagnum peat moss in both commercial and DIY potting soil blends. It is often sold in compressed bricks; coir fiber is considered by many to be more sustainable than sphagnum peat moss. 

Perlite – perlite is mined volcanic rock. When heated, it expands, making perlite particles look like small white balls of Styrofoam. It is a lightweight, sterile addition to bagged and DIY potting mixes. It can hold three to four times its weight in water, increases pore space, and improves drainage.  It has a neutral pH and can be found at garden centers.

Vermiculite – a mined mineral that is conditioned by heating until it expands into light particles.  It is used to increase the porosity of commercial and DIY potting soil mixes, increase the content of calcium and magnesium, as well as increase the water retention of the mix. 

Sand – coarse sand improves drainage and adds weight to potting mixes. Fertilizers act more quickly in the soil if the amount of sand is higher. It helps in proper airflow in the soil. It will help ensure your plants get enough oxygen.

Limestone – you can add pulverized calcitic or dolomitic limestone to peat-based potting soils to neutralize the pH level. Use about ¼ cup for every 6 gallons of peat moss.

Fertilizers – you will need to add fertilizer to peat-based potting soils because the mixes do not naturally contain enough nutrients to support optimum plant growth.  A good potting soil recipe includes a natural fertilizer, derived from a combination of mined minerals, animal by-products, plant materials, or manures. 

Composted wood chips – these lighten up potting soil mixes by increasing the pore sizes, and allowing air and water to travel freely in the mix.  They are slow to break down but could rob nitrogen from the soil as they do, so adding a small amount of blood or alfalfa meal is necessary when using composted wood chips.  You can easily DIY this – get a load of wood chips from a local arborist (like 4 Seasons Arborscapes!) and let the chips compost for a year, turning every few weeks.

Compost – compost is an excellent addition to your DIY potting soil. It contains billions of beneficial microbes, has a superior water-holding capacity, and a decent nutrient content. It is huge in promoting healthy plant growth.

Rice Hulls – this is one of the most sustainable soil amendments available for improving drainage, water holding capacity, and aeration.  Unlike perlite and other rock products, it does not require mining. Rice hulls are the husks that are removed from each grain of rice after harvest. The hulls are parboiled at a high enough heat to sterilize any grains of rice that make their way into the mix. They add nutrients to the soil as they break down. For potting soil, rice hulls should make up 10-50% of the mix.