Make Your Own Potting Soil

Did you know commercial potting soil often contains questionable ingredients, like sewage sludge? It’s true. That “compost” listed on the bag could be made from human waste, plus all the other nasties that end up in our sewer system – things like cleaners, pharmaceuticals, motor oil and fertilizers. If that doesn’t sound like something you want to grow your food and flowers in, do what I do, and make your own potting mix. It’s really easy to do, and may even save you some money.

Before I share my potting mix recipes, let’s look at the ingredients that typically go into potting soil, so you’ll understand their purpose.

Potting Soil Ingredients

Sphagnum Peat Moss

Peat moss is relatively light-weight, even when it’s wet, so it’ll keep your flower pots from getting too heavy. When mixed with soil or compost, it helps to hold water, and keeps the soil from drying out too quickly. It also supresses diseases that can harm seedlings. Peat moss is hard to get wet, so it’s best to wet it before you add it to your other potting mix ingredients.

Coir

Coir is made from shredded coconut husks, and is a waste product of the coconut industry. It’s sold as a condensed brick, which you have to rehydrate before using. It’s marketed as an alternative to peat moss. When added to potting mix, it helps to retain water.

It should be noted that there’s a bit of controversy as to whether peat moss or coir is the more environmentally-responsible choice. Use whichever one you feel comfortable with. My potting soil recipes work with either.

Perlite

Those little white flecks in potting mix that look like Styrofoam are actually perlite, a form of expanded volcanic rock. It’s added to improve aeration and drainage. Since perlite is incredibly lightweight, it’s the perfect soil amendment for containers. When working with perlite, wear a dust mask and keep the perlite wet, so it doesn’t create dust.

Vermiculite

Made from mica clay, this is another soil amendment that can be added to potting mix to improve aeration and drainage. You’ll pay a bit more for vermiculite, but it’s been shown to hold more water than perlite, so you may not have to water as often.

Sand

Coarse, construction-grade sand is sometimes added to potting mix to improve aeration and drainage, but it adds a lot of weight to containers. Go with vermiculite or perlite, if you have a choice.

Garden Soil or Compost

On its own, soil/compost is too heavy and poor-draining to be used in flower pots and container gardens. To overcome this, it’s typically combined with peat moss and either perlite or vermiculite. This results in a light-weight mix that holds water, without becoming water logged, so your potted plants get all those vital soil nutrients, with none of the drawbacks. Use sterilized garden soil or compost in your potting mix to avoid disease, insects and weeds.

Ever wondered why there’s no soil in seed starting mix? That’s because it’s dense, heavy texture is hard for seedlings to push through.

Potting Soil Recipes

Both of the potting soil recipes that follow are written in parts, so you can make as much or as little as you need. A part can be a measuring cup, a flower pot, a wheel barrow – whatever makes sense for your current potting soil needs.

Wear a dust mask to protect your lungs from any dust you may stir up. Working with moistened ingredients will help to minimize dust, and make the ingredients easier to mix together.

Soil-Based Potting Mix

This mix is good for potted plants and container gardens. It’ll keep your containers from getting too heavy.

Cost to Make: $7.76 with perlite, $8.76 with vermiculite (for 1.5 cu. ft.)
Cost to Buy a Bag of Potting Mix: $7.47
Savings: No savings to make your own, but you’ll know you’re getting a quality potting mix.

To make a batch, combine:

1 part sterilized garden soil or compost
1 part moistened sphagnum peat moss (or coir)
1 part moistened perlite, vermiculite or sand

If you use a good quality soil in your mix, it probably won’t be necessary to add any fertilizers for a while. You can always do a soil test to see. Your goal should be a pH between 6.0-7.0. Amendments, like lime, blood meal and bone meal can be added, if necessary. Consult the bag to determine how much you should add to your potting mix.

Soil-Less Potting Mix ( aka Seed-Starting Mix)

This mix is good for seed germination. It has a light, loose consistency, which makes it easy for seedlings to emerge and roots to grow.

Cost to Make: $2.40 for 12 quarts
Cost to Buy a Bag of Seed-Starting Mix: $4.97
Savings: $2.57 (a savings of over 50%)

To make a batch, combine:

1 part moistened sphagnum peat moss (or coir)
1 part moistened perlite or vermiculite

While peat moss holds water well, it’s difficult to rewet, so try not to let your seedlings dry out.