Mama used to threaten to wash my mouth out with soap, in those long ago days of my childhood, if she heard me repeat certain words. Believe me, I took those words out of my childhood vocabulary!
There is one word I do not use today when I discuss African violets. My violets are NOT planted in (oh, horrors! Cover your ears; close your mouth)…… SOIL.
In 1985 Pauline Bartholomew explained why in her book Growing to Show-How to grow prize-winning African Violets. “Few growers now include natural soil in potting mixes. Soil has too many drawbacks…………….. It tends to compact rapidly, has poor aeration, and must be pasteurized before use.” (page 50-Potting Mix)
In 25 years great advances have been made; almost no commercial potting mix contains soil. Potting mixes are made using three basic ingredients, perlite, course vermiculite, and peat moss (or composted forest products); the pH balance is achieved by using dolomitic limestone.
Recognizing the role of each of these staple ingredients helps me understand the advantage of the soil-less mix.
Knowing the role of each ingredient helps me when I modify my favorite commercial mix.
When I assemble my mix from scratch, I understand why I am using particular proportions.
Getting the facts
Let us gather some common household items that may help us better understand the function of each ingredient in our potting mix recipe.
- plastic dish scrub pad
- sponge (cut it into small pieces)
- small bowl of animal feed bits, imagine it saturated with lemon juice before being dried
Perlite: Notice the makeup of the scrub pad. It is bulky, nonporous fibers, bundled in a shape with a lot of air space inside. Pour water through it. What happens, does it absorb the liquid? No. Is it wet? Yes, a film of liquid clings to the surfaces of the fibers. Try squeezing water from it, nothing happens. Alone it has no odor, will not decompose; it is a bulky mass that will not compact easily.
A perfect description of perlite and it’s function in our soil-less mix !
“Perlite is a unique volcanic mineral which expands from four to twenty times its original volume when it is quickly heated to a temperature of approximately 1600-1700 degrees F.
“Because of the physical shape of each particle, air passages are formed which provide optimum aeration and drainage. Because perlite is sterile, it is free of disease, seeds, and insects.”
Vermiculite: Pour water through the sponge. It immediately absorbs and holds volumes of fluid which can be released by squeezing. Additives to the water used will be held for slow release, the sponge will not decompose. Even when dry these sponge particles will not compact. Neither will vermiculite.
Peat Moss (or composted forest products). Think of the bowl of pet feed bits having been saturated with lemon juice then dried. It will absorb enormous volumes of water, quickly break down, the products of the breakdown will be distributed to any material touching it. When it dries it is difficult to rehydrate; it forms a tightly compacted mass, not easily broken apart.
“Peat moss does not contain nutrients but it absorbs nutrients both already existing in the soil and those added by you. The cell structure of sphagnum peat moss is large so it can absorb extra air and nutrients like a wick or sponge. By absorbing these important nutrients, peat moss then releases them over time as your plants need them.”
Dolomite Lime: Many growers add a small amount of dolomite lime to control the pH. As sugar “sweetens” the acidic lemon juice making it more palatable to us, dolomite lime counteracts the acid pH of the vermiculite and compost (peat moss) helping to maintain the pH range of 6.4 to 6.9
Most practical for the newbie
Can I just go to a store and buy premixed African Violet potting mix?
Sure, in fact, that is what I do. An advantage when using a good commercial mix is the pH adjustment has been made so there is no need to be concerned. I amend the commercial mix with perlite (a neutral pH) for the fluffier mix I prefer.
A word of caution: There are good mixes and not so good. The cheaper mixes may have large chunks of wood products and other inferior ingredients. You will find, as you experiment, a favorite supplier. I use Miracle-gro or Fafard usually, others prefer Promix and Volkmann mixes.