As the saying goes, “essentially, all life depends on soil.” African violets are very particular with their soil requirements, and they would prefer a light and porous mix. Starting with the correct medium and spot will allow these delicate pots to develop healthy shoots and blooms.
It is helpful to understand this plant’s natural habitat to use basic principles for indoor raising. Understanding the soil needs is very important when it comes to African violet care.
Referencing the Natural Habitat
In the wild, these gesneriads occur on mossy, rocky slopes. Some rock substrates are made of limestone nourished by piled-up organic debris. Healthier rosettes were observed to be well-spaced and trailing along with the steepness of the substrate. Those that are exposed to direct sunlight tend to dry out compared to being under the shaded regions. Larger varieties prefer humus-rich rock covers.
Components of a Culture Medium
Nowadays, readily prepared potting and growing media are widely available in stores. The three most recommended ingredients of the potting mix are sphagnum peat moss, vermiculite, and perlite. Each component constitutes a hospitable profile for African violets, which is ideally well-drained, well-aerated, with a balanced to slightly acidic pH and minerals, and can retain enough water and nutrients.
Partially decomposed green organic matter, especially mosses and leaves, in acidic-anaerobic and moist conditions, can be sourced from the wetlands and are further ground and dried resulting in peat. The ready-to-use phase would resemble a typical soil, but with less density, a pH of 3.5 to 4.5, and significant water content. Coco coir and coco peat are great alternatives but are less acidic and can decrease aeration over time.
Volcanic sites can be mined for vermiculite, which is a huge industry in the USA and South Africa. It comes in the forms of shiny, grayish-brown, or silvery-gold rock flakes, or mica rocks, with a neutral pH of 7.0 to 7.5, that expands when heated, and then further refined into smaller pebbles. This structure allows water and nutrient absorption and retains minerals such as magnesium, calcium, and potassium.
Vermiculite provides added insulation in the root zones, which can slightly speed up the growth of new shoots in saintpaulias without compromising the health of new plantlets.
In colder climates or seasons, repotting African violets with the addition of vermiculite works as an insulator that promotes root-zone heating which also increases the surrounding air temperature, at least slightly above the level of the medium.
Perlite is also a volcanic mineral that improves drainage and prevents waterlogs. It arises from superheated volcanic glass that expands and pops to form lightweight pebbles, thus the term ‘volcanic popcorn’. The holes ensure the entry of oxygen, thus complementing vermiculite, but it cannot retain nutrients. A substitute is sand or pumice.
The standard is a 2:1:1 formulation of peat moss, vermiculite, and perlite especially for starting medium. A 1:1 ratio is also good for purposeful repotting, half for peat moss while the other is a choice of either vermiculite or perlite, with good knowledge on what each can foster. In some cases, store-bought mixes can be added in a 1:1:1 ratio with peat moss and again either vermiculite or perlite.
Other Matters to Consider
Store-bought media typically contain fertilizer or microbes, so liquid plant food must be in lower doses for at least two months or until symptoms of under fertilization appear. Typical potting mixes for houseplants contain organic matter which is not fit for African violets as it promotes water retention. However, compost can be used as fertilizer or mixed with the medium in small quantities for added nutrients.
Soil Moisture and pH
Watering goes hand in hand with the quality of the potting mix. Ideally, the medium should not be completely dried in between watering, and must also not be flooded and soggy. If salts accumulate, they will show as browning or burning of the foliage, if not wilting and constriction of the stems due to clogged water and nutrient uptake. Too much acidity can be remedied by adding lime or calcium carbonate.
Growing Medium versus Potting Mix
A potting mix has a more controlled formulation and specific components. On the other hand, a growing medium can be adjusted especially when plants increase in size and are finally repotted. The roots of saintpaulias are sensitive to even minor changes in the soil. A good approach is to create a fresh batch of almost the same components as the potting mix, with added compost for nutrients. The amount and frequency of fertilization should still be the same.
Can I use succulent soil for African violets?
Most succulent mixes, same with store-bought ones specific for AVs, are too heavy for these gesneriads. For African violets, mixing with perlite in a 1:1 formulation will have better results.
Will cactus soil work for African violets?
A cactus essentially thrives better with a higher proportion of sand in its potting mix, but it can also work well for saintpaulias. Cactus medium is usually slightly more alkaline compared to the one for AVs which is acidic and can retain more nutrients and moisture. A remedy for this is to add peat moss to the mix, starting with 1:2.
What is the difference between African violet potting soil and regular potting soil?
Regular potting medium, especially those made for houseplants, tends to retain higher moisture and is more compact. It is also likely enhanced with more fertilizer, which can be too heavy in growing African violets. They would need more aeration and better drainage. The medium may use less outdoor soil with fertilizers and more peat moss, vermiculite, and perlite, with the final mix being slightly acidic.
Johansson, D. R. 1978. Saintpaulias in their natural environment with notes on their present status in Tanzania and Kenya. Biological Conservation, 14(1), 45–62. doi:10.1016/0006-3207(78)90005-8
Missouri Botanical Garden. N.d. African Violets. Missouri Botanical Garden: William T. Kemper Center for Home Gardening. https://www.missouribotanicalgarden.org/Portals/0/Gardening/Gardening%20Help/Factsheets/African%20Violets2.pdf
Perry, L. 2016 Nov 30. African Violets: Seven Steps to Success. University of Vermont Department of Plant Soil Science website. https://pss.uvm.edu/ppp/articles/afrviolets.html
Perry, L. 1998 Dec 17. Your African Violet. University of Vermont Department of Plant Soil Science website. https://pss.uvm.edu/ppp/articles/africanv.html
Thomas, P. A. 2012. Growing African Violets. The University of Georgia College of Agricultural and Environmental Sciences, Cooperative Extension Circular 660. https://secure.caes.uga.edu/extension/publications/files/pdf/C%20660_2.PDF
Vogelezang, J. V. M. (1988). Effect of root-zone heating on growth, flowering and keeping quality of Saintpaulia. Scientia Horticulturae, 34(1-2), 101–113. doi:10.1016/0304-4238(88)90080-5
Worrall, R. J. (1981). Comparison of composted hardwood and peat-based media for the production of seedlings, foliage and flowering plants. Scientia Horticulturae, 15(4), 311–319. doi:10.1016/0304-4238(81)90085-6
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