Mixing It Up

Written for the 2019 November-December issue of the African Violet Magazine

By Sandra Skalski, Columnist of “My First Violets”

Whether your first violets are starter plants or mature plants, at some point, you will need to repot them. Repotting once or twice a year enhances growth, and fresh growth encourages blooming. What will you use for a potting mix? My first violets were gifts from my grandmother when I was 10 years old. As a young girl, I had no idea what a “soilless mix” was, and even if I knew, I still would have selected the closest thing at hand… the endless supply of soil in my backyard. That wasn’t the best decision and those violet are long gone, but now I know a good deal more about what makes a good potting mix for African violets.

What does a potting mix do? Physically a potting mix provides a substrate to anchor the roots for the plant to grow. It makes water and oxygen available to the roots. Chemically , the mix holds the nutrients the plant needs. In the wild, African violets grow in crevices and loose substrate on rocky cliffs or porous rocks. You want a potting mix that approximates these conditions: evenly moist but well-draining, slightly acidic, and with a loose crumbly texture. Potting mixes suitable for African violets contain no actual soil’ that is why they are called soilless mixes. Here are some tips to help you make a good decision for your plants’ mix.

POTTING MIX INGREDIENTS

The most common ingredients in potting mixes are sphagnum peat moss, perlite, vermiculite and dolomite lime. Sphagnum peat moss comes from a bog plant that grows in low-pH, poorly draining environments. Since other plants cannot grow under these conditions, peat moss is free of weeds and weed seeds. It also has good water-holding capacity, which makes it ideal for houseplants and container gardens.

Perlite is made by heating a type of volcanic rock to a very high temperature. The water trapped in the rock expands, creating a light, porous material. There are various type of perlite, sorted by the average size of the particles, from very fine to quite chunky. Look for coarse or horticultural grade perlite. If it is sold by a numerical grade, look for grades 3 or 4.

Vermiculite is made by heating up a type of laminated rock. It expands into a very light material that has excellent water-holding capacity and can improve soil aeration. In general, perlite drains better than vermiculite.

Dolomite lime is a powder-fine ground rock that is used to adjust the pH and add calcium and magnesium to the potting mix. Most peat moss has a pH of around 3.5 to 4, which is well outside the ideal pH for African violets and most other plants. Unless you are buying pure peat moss, most commercial potting mixes have some added dolomite lime to adjust the pH. Be sure to look for the powdered dolomite. The granular type is for lawns and gardens.

Coir now is included in many commercial potting mixes. Coir is ground-up coconut husks. Compared to peat moss, coir has higher water retention, a finer texture and a neutral pH. Many growers have had success using this material, but I have found that I need to use a lot more perlite to make a mix suitable for wick-watering.

YOUR POTTING MIX

There is no single, perfect potting mix. The best potting mix for your plants depends on your growing conditions, including the general temperature and humidity, and how your water and fertilize your plants. If you wick water or mat water, you will want to use a potting mix that contains 40% to 60% perlite. If you buy a ready-made mix, look for words like “wicking mix” to let you know that this is a well-draining material.

The African violets you buy in the supermarket or big box store might be in a much heavier mix that holds a good bit of water. This makes sense because once these plants leave the greenhouse, their care won’t be as consistent. When people get them home, it is easy to overwater them and kill them with kindness. Your violets still can grow in these mixes as long as you are careful to water them only when the top inch or so of the soil feels dry to the touch.

If you are a new grower with a small number of plants, consider getting your potting mix from one of our AVSA commercial growers or an eBay supplier recommended by another grower. They’ve already done the work for you to blend an optimal mix, especially for African violets. As a new grower, you have many things to learn, and having a tried and true potting mix can eliminate one variable.

Many popular horticultural supply companies offer bags of potting mix especially for African violets. They usually come in 8-quart sizes, so it is ideal for the hobbyist with a small collection. Some of these mixes contain fertilizer, so if you choose to use them, be sure to cut back on your own fertilizer for the first few months after you repot. These blends are sold to be used straight out of the bag, but they generally are heavier mixes with very little perlite. I have had success mixing these blends evenly (50/50) with coarse perlite or a 40% mix to 60% coarse perlite. The percentage of perlite can vary because of factors like coarseness or individual growing conditions. Even variations in the base mix can affect the water-holding capacity of the final product. Start with a 50/50 blend and adjust as needed.

If you have a lot of plants or you just like to “do it yourself,” you can easily blend your own African violet potting mix. A good place to start is with either Pro-Mix BX or Pro-Mix HP, or a similar commercial mix. These brands are readily available in garden centers or horticultural supply stores. One drawback is that the base-mix comes in large bags or compressed bales. Depending on the number of plants you have, that might mean you have a very large supply of potting mix.

If it seems like that much potting mix will be more than you can foresee using, consider teaming up with your local club or growing friends to share the cost of materials. Mixing up a good potting mix could be a fun club activity, and a good opportunity to learn about potting mix and repotting violets. There are a lot of good recipes, probably as many as there are growers. Talk to successful growers; most of them will be happy to share their recipes.

OTHER ADDITIONS

I don’t add vermiculite to my potting mix because I wick water, and I think the vermiculite makes the mixture hold too much water. The Pro-Mix I use contains mycorrhizae, which are beneficial fungi that have a symbiotic relationship with the roots and enhance their ability to absorb water and nutrients. Since the mycorrhizae in the base mix don’t have a long shelf-life, I add some additional mycorrhizae before I pot up my plants. I adjust my pH with dolomite lime to a range of 6.5 to 6.8. This is a good pH range, however many successful growers do not test or adjust their pH since most base mixes already have some dolomite lime added.

You might have read a lot about fertilizers and additives some growers include in their potting mixes. Before you start adding a laundry list of “special” additives, be sure first that you can tell whether any positive or negative changes to your plants are related to the potting mix and not some other change. No matter how promising you think the improvements or additives are going to be, try the new mix on just a few plants at first. Even the most experienced growers have made the mistake of moving an entire collection to something new, only to discover weeks or months later that perhaps they should have given it a test-drive first.

That wasn’t so hard, was it? Is it time for your plants to be repotted? Buy some of your favorite mix or mix up a batch and get to it. No matter what potting mix you choose, you will find that the best “additive” of all is your time and consistent care.