Soil and Additive Testing – Part 1

Soil mixes for growing African Violets are as unique as the growers themselves.  Nearly every grower has his or her own preferred “recipe” with some being as simple as a commercial soil blend to complex formulas with additives such as perlite, vermiculite, fertilizers, etc. For my own growing, I have always been partial to Pro-Mix, a peat based potting soil.  I typically mix Pro-Mix 50/50 (by volume) with perlite to lighten the mix as I bottom water in community trays.

As with opinions on potting blends, opinions on peat moss vary.  Some claim that it is a renewable resource while others point to disrupted ecosystems left after harvesting occurs.  Regardless, peat moss is an acidic material which deteriorates over time.

An alternative to peat moss is coco coir.  This material comes from coconuts and is treated to remove salts before being sold as a potting soil. It is typically sold in compressed bales which expand when water is added.  The brand I am using for my testing is by Hydrofarm and is sold as Grow!t Coco Coir Mix.


I am testing various soil blends utilizing coco coir and peat moss to see which performs best in my conditions.  It is important to note that what performs best in my conditions may not necessarily be the best in other conditions – watering style, temperature, humidity, etc all play a role and vary for each grower. There are several factors which I want to compare and analyze. Keep in mind for all of this that I am not growing on a hobby scale and my goals are somewhat different from a hobby grower. I want to quickly grow a healthy starter plant with a strong root system.  While I do maintain many adult plants which are used for harvesting leaves, I do not focus on growing show plants and I prefer not to keep my starter plants around long enough that they would need repotting.

The formulas which I am testing are:

  • Pro-Mix BX mixed 50/50 with coarse perlite
  • Coco Coir mixed 50/50 with coarse perlite.

These are my bases with no additives.  In addition, I am taking each base blend and testing four additional additives for a total of ten soil blends.  The additives are:

  • Plant-Tone fertilizer by Espoma (1/4 c per gallon),
  • Wiggle Worm earthworm castings (1 c per gallon),
  • Dehydrated Super Manure by Hoffman (1/4 c per gallon), and
  • dolomitic lime (1/8 c per gallon).

The blends are going to be tested by analyzing the following: monitoring pH levels and visually comparing growth of the plants (speed to produce plantlets, first blooms, root growth, overall plant growth/health). The entire cycle will be tested, starting with leaves being set in each blend and the resulting plantlets being potted up into the same blend.  All blends will be treated the same – bottom watered and fertilized with Dyna-Gro.

In order to have a sample size large enough to get results I feel are meaningful, I am starting with (45) 3oz pots per blend (a 1020 tray full).  I will be setting numerous varieties of leaves with the leaves of each variety randomly distributed among the blends. I do not expect to set 10 leaves from 45 varieties, probably 5 leaves from 90 varieties, but the overall growth patterns should provide me with the information I need.

Leaves set in 10 soil blends

While working with these to fill the initial test trays, I noted some pros and cons of each base.

Coco Coir


  • “Flowed” nicely for filling cups
  • No debris/sticks
  • Easy to store – highly compressed bale
  • Delivered to my door
  • Easy to handle – lightweight bale


  • Not available locally (carried by most hydroponic stores if you have one nearby)
  • Takes time to hydrate bale



  • Available locally (most seed and feed stores carry)
  • Ready to use out of bale


  • Contains minimal debris (a few sticks)
  • Heavy bale (I can haul it, but a bale weighs in around 60 lb.)
  • Bulky bale (I only buy two at a time because they take up a lot of room)
  • Occasionally I find some surface mold on the potting media in the bale
  • Expensive to have delivered

Goals and Expectations

My goal is simply to determine which base works best in my environment. These were two potting materials which are readily available and relatively inexpensive. The cost of the two is comparable (Pro-Mix is approximately $4.29/cu ft (excluding gas) and coco coir is approximately $4.40/cu ft (delivered)).  I am hoping to see the pH levels remain more stable in the coco coir.

I am doubtful of seeing any significant difference from the base with the worm castings.  The recommended usage rate was 3 parts base to 1 part castings.  I did not come near this rate; it would have made the mix very heavy and expensive.

The SuperManure was selected after attending a presentation by Marie Burns and Pat Hancock at the 2015 National AVSA Convention.  Ms. Hancock noted that she had used this or a similar product in her soil blend.  However, if I understood correctly, the Turners of Starz and Streps experienced salt buildup from the additive which harmed their plants and they discontinued its use.

The PlantTone by Espoma is an organic fertilizer. I use their products exclusively in my home gardens, both vegetable and perennial.  I selected the product to test due to my satisfaction with the products.

If there is no noticeable difference, I will transition to the coco coir for the pros noted above. My main concern with the SuperManure and PlantTone is fertilizer buildup/burn on the plants.