Soil-Less potting mix may seem like a misnomer… after all, it looks like dirt, doesn’t that make it soil? Not so much- here’s why . . .and HOW to make your own!
Soil from your garden or yard contains many things including, but not limited to sand, compost, clay, disease spores, bacteria, plant eating insects, worm castings, and is quite heavy. It can easily compact around the roots of plants, oftentimes choking out the plants ability to get proper aeration around the roots. You can kill off many of the pathogens and pests by simply solarizing the soil first. Cover a pile with clear, plastic sheeting for 4-6 weeks.
Soil-less potting mixes are made of a mixture of Sphagnum peat moss, Coir, Perlite, Vermiculite, dolomitic limestone, and just as often- a wetting agent.
Sphagnum Peat Moss(or other types of Peat) – Unfortunately peat moss takes hundreds of years to form, so it’s not particularly environmentally sustainable. Having a pH of around 5.8 Peat is relatively acidic and works well for starting seeds and breaking through the germination stage. Peat drains exceptionally well while staying moist, it’s also very lightweight and inexpensive.
Coir – a suitable replacement for Peat Moss, Coir is a coconut fiber and is considered a by-product of the coconut industry. It provides ample drainage, whilst retaining proper amounts of water, much like Peat Moss.
Perlite– this is probably the easiest “ingredient” to notice in commercial blends as it looks like styrofoam dots. Perlite is actually a volcanic material that adds drainage and water retention properties to the mixture. Inclusion of perlite in homemade mixes is particularly helpful during germination as it allows the mixture to remain consistently moist.
Vermiculite- another easy to spot ingredient, Vermiculite are the shimmery gray flecks (almost Mica-like) in appearance; that when heated expand, allowing them to soak up necessary water and nutrients. There are different grades of vermiculite available (as it is also often used in Construction) but it is not recommended to use building grade vermiculite as the water retention properties are different. Use garden grade vermiculite instead!
Dolomitic Limestone– There are a couple common types of limestone (Calcitic and Dolomitic). In our soil-less mixture we’re opting for Dolomitic Limestone because it is a combination of calcium carbonate and magnesium carbonate. It neutralizes acids while providing calcium and magnesium. Dolomitic limestone also dissolves more slowly than calcitic limestone, lasting an average of 2-4 months (as opposed to 6-8 weeks). It creates a pH stability buffer, if you will.
Wetting Agent– These are polymers that are added to the mix to improve the absorption of water. They aren’t very biodegradable (which actually would defeat the purpose!). Watering plants from the bottom actually helps reduce (or removes!) the need for a wetting agent.
When it all comes together
As the mix comes together it should provide adequate drainage, aeration, water retention, nutrient retention, vital nutrients (aka plant food!), support and natural microbes.
Which one Should I Use?
Self Watering Plants– If you want self-watering plants that require little attention, you’ll want to use a moisture wicking soil-less potting mix.
Hydroponic Plants– if you’re wishing to start your own hydroponic system, opt for clay pebbles or a soil-less potting mix
Weed-Free Gardening– you’ll want to use a quality potting soil, which allows for proper aeration around the roots of the plants.
Homemade Soil-Less Potting Mix Blend:
Add ½ cup each per every 8 gallons of mix:
½ cup Dolomitic Limestone (Raises soil pH and provides calcium and magnesium)
½ cup Blood Mealor Soybean Mealor Dried Kelp Powder (Nitrogen)
½ cup Bone Meal (Phosphorous)
While these can sound expensive, most can be found for under $7 dollars and last a Very long time (after all, you’re using about 1/2 cup at a time).
Here’s how to make your own Self Watering Planters.