How to Make Soilless Potting Mix

Hands mixing potting medium

Purchase a pre-made soilless potting mix or mix your own growing medium. Image from UW Garden Guide.

Flowers springing merrily from dirt-filled pots and planters is a sight that we take for granted. After all, aren’t plants supposed to thrive in dirt? The truth is, planting in containers requires a little more finesse, since you’ve got to encourage the medium to hold moisture against the plant’s roots while draining away any standing water to prevent drowning them.

It’s lucky for us, then, that agricultural scientists realized that by using soilless potting mix, both goals can be accomplished simultaneously, while still creating a sterile growing environment for plants that might be susceptible to soil-borne diseases.

What is Soilless Growing Medium?

Soil less growing media is exactly what it sounds like: a material designed for growing plants that contains no garden soil, sand or clay. Soilless potting mixes have a light texture, creating an ideal environment for seeds to germinate and roots to penetrate deeply without obstacles. It’s important that plants in containers are able to gather nutrients as efficiently as possible because they can’t spread far.

Creating the best soilless mix is the aim of many home gardeners, who start with a basic soilless mix recipe and make subtle changes until it meets their needs. Most recipes have a few common ingredients: a material to hold water, another to prevent compaction and something to provide fertility. When these elements come together properly, the end result is a mix with a near-neutral pH to ensure the optimal utilization of nutrients in the plants you grow.

<a href=


Worm Castings in Soilless Mixes

Researchers experimented extensively with worm castings and their effects on plants in the 1980s, and came to a few conclusions:

  • Worm castings contain similar nutrients to other organic fertilizers, but because of the biology of the worms, the nutrients are in forms more useful to plants. Other organic fertilizers rely on microbes to break them into useable forms – it takes time to acquire these tiny helpers in sterilized medium.
  • Vermicompost (worm castings with some worm bedding left behind) encourages faster germination of seeds than commercial growing media. Plants in their tests also grew bigger in vermicompost-based mixes.
  • Mixing vermicompost, which tends to have a high pH, with peat, which tends to have a low pH, creates a medium with a naturally neutral pH. A medium with this combination of materials does not usually need the pH artificially adjusted, simplifying the work of the container gardener.

For these reasons, we recommend adding worm castings to soilless growing mixes.

Soilless Mix Recipes

A basic, but effective soilless potting mix starts with peat, perlite and an organic fertilizer, such as worm castings. For transplants, mixing one part peat, one part worm castings and one part perlite, by volume, creates a suitable medium. Seed-starting mixes should contain half as much perlite to help seedlings maintain a slightly higher humidity level. Adding about a half-ounce of Epson salts per cubic foot of either mix will create a complete nutrient profile.

Worm casting fertilizer from Hooks & Lattice will turn your soilless potting mix recipe on its ear, adding a fertilizer that can last all year while helping to maintain proper moisture for your plants. Available in both five and 10-pound bags, our worm casting fertilizer is ready for any size container garden.

0 replies

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *