Are you container gardening this year, or do you have many flower pots to fill? Try making your own potting mix with just a few ingredients!
Have you noticed the prices for potting mix recently? Eek! One bag might fill up one or two containers; three at best, if they are small. But I have 16 grow bags I want to fill this year which means I need over 100 gallons of potting mix. The cheapest potting mix I found near me is $5 for 1.5 cubic feet (just over 11 gallons.) And that is the regular, non-organic stuff. Organic potting mix is over $7 for just 1 cubic foot (about 7 1/2 gallons.) I would need 9-13 bags of potting mix to fill all of my grow bags, plus more if I wanted to do some flower pots.
I decided instead to buy some ingredients and make my own potting mix.
Is Potting Mix the Same As Soil?
Potting mix and garden soil are not the same thing. Most potting mixes do not actually have any soil in them! They contain a mixture of materials that are good for both moisture retention and drainage. (These seems like opposing ideas, but both are important for your plants to be healthy.) They often have some kind of fertilizer in them as well. Potting mix is light and fluffy, and is used for plants grown in containers
Garden soil is heavier and is typically a mixture of topsoil and compost. It is used for in-ground garden beds and larger raised beds. Soil often contains fungi and other pathogens that could affect your container plants. You can read more about the differences between potting mix and garden soil here.
What Ingredients Are In Potting Mix?
Potting mixes contain some mixture of these ingredients (but rarely all of them).
Peat moss
Peat moss is the accumulation of layers of decaying organic material (mostly dead sphagnum moss, some other plants, and sometimes insects) that accumulates over thousands of years on the surface of bogs.
This popular gardening product is great for water retention (up to 70% of its volume!). It is acidic (so lime is often used to counterbalance the pH), and it helps amend garden soil as its organic materials break down.
Peat moss and sustainability*
Harvesting peat moss is not a sustainable or environmentally friendly process. Harvesters drain bogs (even if only temporarily) releasing high amounts of carbon into the atmosphere, and it takes between 5-20 years for harvested areas to regain ecological balance. When the peat is able to grow again, it takes 15-25 years to accumulate 1 inch.
For this reason, I chose not to use peat moss when I made my potting mix.
Sphagnum moss
Sphagnum moss and peat moss are similar products. In fact, they are basically different parts of the same plant. But the way they are harvested have very different environmental impacts.
Sphagnum moss also grows on the surface of bogs, but it is a living plant that is harvested and dried for commercial use. It also is great at retaining water, and it has a more neutral pH than peat moss. The growing cycle for sphagnum moss is 5-6 years, so with careful harvesting, it is a more sustainable and environmentally friendly product than peat moss.
Coconut Coir
Coconut coir (pronounced “coy-er” in the US) is made from the husks of coconuts and was once considered a waste product. Though it does not contain nutrients necessary for growing plants on its own, coir helps soil and potting mix have better water retention and/or drainage as needed.
Coir usually comes in the form of dehydrated bricks which need to be rehydrated before using them. The bricks will expand 5-7 times their original size.
Compost
Compost is organic matter (like food scraps, leaves, and animal waste) that has started to decompose. It looks like dark, rich dirt and it is great for making and maintaining healthy soil. Compost introduces microorganisms and nutrients that feed your soil and help it to become better at controlling moisture. You can read more about compost here.
Perlite
Perlite is made from tiny pieces of volcanic glass that puff up when exposed to high heat and pressure (like popcorn), and it looks like little balls of styrofoam. It also does not contain nutrients, but helps to aerate and loosen soil and potting mixes to create a well-draining planting medium. Perlite also has water retaining properties.
Vermiculite
Vermiculite is another heat-treated naturally occurring mineral. High pressure and heat cause the phyllosilicate minerals to puff up and expand (kind of like perlite). The particles end up looking kind of like tiny, flaky worms. Vermiculite can hold up to 4 times its volume of water, and it also helps lighten soil and improve drainage.
Fertilizers
Plants need Nitrogen, Phosphorous, and Potassium (the N-P-K numbers you see on fertilizer packaging), plus calcium, magnesium, sulfur, and other trace minerals. There are many organic and non-organic fertilizer options that I am not going to go into detail about, but for potting mixes, slow release fertilizer options are best.
If you are container gardening, you should probably also add fertilizer during the growing season, because even slow release fertilizer can get diluted and run-off after watering.
Potting Mix Uses
Potting mix can be used for flower pots and vegetables and herbs grown in containers. Just be aware that different kinds of plants have different needs. For example, succulents and tomatoes should NOT use the same type of potting mix, because they have different water needs. Fruits like blueberries prefer a more acidic planting medium than your average vegetable needs. You may have to do some homework to figure out what specific soil requirements your plants have.
How I Made Potting Mix
My potting mix ingredients
Like I said earlier, I needed over 100 gallons worth of potting mix, so I bought 1 cubic yard of compost and used that as my main ingredient. Additionally I used coconut coir (because of the environmental issues related to peat moss), vermiculite, and worm castings. I also added bone meal to my carrots and potatoes to give them extra phosphorus.
I chose to use vermiculite instead of perlite, because grow bags are porous and therefore good for drainage; vermiculite is better at retaining water. Plus, I found it cheaper in my area. Apparently perlite is still back-ordered in many places after the pandemic.
I should have used a dust mask when mixing in the vermiculite to protect my lungs from the mineral dust. Now I know and you do too! Be safe!
My potting mix ratios
Most of the potting mix recipes I have seen used different ratios, but I am a “use what you got” type of person. My potting mix used roughly:
- 4 parts compost
- 2 parts coconut coir
- 1 part vermiculite
- 1 part worm castings
Now it is time to get your hands dirty. Happy gardening, Friends!
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