Potting soil is one of the most useful garden materials. With a coarser, looser texture than garden soil, it can be used for starting seeds, growing plants in containers, or nurturing cuttings and transplants. Potting soil is designed to provide an easy medium for root growth while also holding the right amount of moisture and providing nutrition for growing plants. Commercial potting soils are widely available and they work quite well. Making our own potting soil offers a number of potential advantages however. It can be more affordable. We get to control the components that go into our potting soil mix, allowing us to tailor it to our own needs. Making potting soil also helps us understand what makes good soil and how the ingredients all work together. So let’s dig in and learn a bit more about making potting soil and how we can make it at home!
Potting Soil Ingredients
When it comes to making our own potting soil, it helps if we start with an understanding of potting soil ingredients and what roles they play in the final product. Potting soil needs to do balance several needs: it must be dense enough to support the plant while being loose enough to allow easy root growth. It should hold nutrients and moisture well while allowing for good drainage and air flow. And it needs to be free of weeds, diseases, and pests that might have a negative effect on plant growth. With all that in mind, let’s look at some possible ingredients for DIY potting soil:
· Garden soil forms the basis of potting soil. You can use inexpensive topsoil from the garden center, but a sterilized loam soil is a safer choice as it is more likely to be free of seeds and diseases. We’ve used regular topsoil for years without issue, however, so take that for what it’s worth.
· Sphagnum moss or peat moss is just that—a dried moss used for a number of gardening purposes. In potting soil, the coarse, spongy texture helps keep the soil loose enough while also providing stability and moisture retention. We recommend soaking sphagnum moss/peat moss overnight before adding it to the mix; otherwise it can be difficult to incorporate and may take time to absorb enough water. We recognize that there are sustainability and environmental concerns around the use of this ingredient; if desired, we can substitute loose compost instead.
· Speaking of compost, it serves many of the same functions in potting soil as it does in many other garden uses. Compost add nutrition and organic matter while also helping to loosen dense soils and improve moisture retention. You can buy compost, of course, but home-made compost can be a real cost saver while also ensuring quality.
· Sand is often misunderstood as a gardening material, but in homemade potting soil coarse sand—also sold as builder sand—can help improve drainage and aeration. Be advised, however, that too much sand can interfere with potting soil’s water retention and also make containers very, very heavy. We’d also like to remind you that despite a popular garden myth mixing sand into clay soils creates something very much like concrete rather than loosening the clay.
· Perlite and vermiculite are distinct ingredients, but they fill similar roles so we’ll discuss them together. Both perlite and vermiculate are lightweight, absorptive materials that help hold water while lightening and aerating the soil mix. They are often used in these roles in place of sand, with the downside that they’re more expensive. Perlite also has the tendency to “float” to the top of the potting mix, but that’s easily remedied by giving it a good stir with our hands before moving it to the containers. Generally speaking, they tend to work better than sand but they can also be quite a pit more expensive so what you ultimately use will depend on how much potting soil you’re making, your budget, and your needs.
There are other ingredients that you may see included in recipes for DIY potting mix, including things like ground limestone, pumice, coconut fibers/coconut coir, and volcanic rock. These tend to be used in potting soils for specialty plants like succulents or cacti. There’s nothing wrong with experimenting with them or using them for a specific need, but for now we’ll focus on an all-purpose potting soil recipe.
Making Potting Soil
Now that we understand what the ingredients do and how they interact, let’s look at a basic recipe for potting soil! Before we start mixing, let’s remember that these are general measurements—don’t worry if you’re not exact. We can adjust the mix later by adding small amounts of various components but we recommend using small amounts, going slowly, and mixing thoroughly to see the results before adding more. So here’s the basic recipe for potting mix—let’s take a look:
· Add one gallon/four liters of top soil or sterilized loam soil to a large, clean container. Use something without holes or vents so you don’t lose your potting mix as you go!
· Then add one gallon/four liters of sphagnum moss/peat moss or compost. Don’t forget to moisten your moss in advance. Mix into the soil thoroughly.
· When the moss and soil have been incorporated, add one gallon/four liters of sand OR perlite OR vermiculite. Just one gallon, not one gallon of each! Mix gently and thoroughly.
· When all the ingredients have been combined into an even, homogeneous mix, it’s time to assess our home-made potting soil. If the soil feels gritty or, well, sandy, there’s likely too much sand and we may need to add more compost or sphagnum/peat moss. If the soil feels too wet, sticky, or heavy, we may need to add additional sphagnum/peat moss, sand, perlite, or vermiculite. It can take a bit of experimentation, so go slow, use small quantities, and observe the changes before adding more.
· And finally: relax! Plants are resilient and adaptable and even if your DIY potting soil isn’t 100% perfect it will almost certainly be good enough provided you pay a bit of attention to the process.
There’s a lot more to be said about making potting soils and container mixes, but this should get you started. As you learn more you can adapt your potting mix recipe to fit your needs—your garden is your own and unique to you! This blog was inspired by a customer question, and we’re grateful they reached out. If you have a recipe for potting mix or container mix you’d like to share, please jump into the comments section or send us an email. Likewise, if you have any questions please reach out. Gardzen is all about community and we love to hear from you!
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