With the right growing conditions, your African Violets can reward you with lush growth and an almost constant supply of blooms. However, growing African violets can be a challenge, especially if you’re not aware of the importance of soil pH.
Soil PH is an unseen factor that affects the availability of nutrients and minerals to the plant, which in turn affects its overall health and growth. In this context, it’s essential for African violet growers to understand soil pH and its impact on plant health to ensure that their plants thrive and bloom beautifully.
What is soil pH?
Soil pH is a measure of the acidity or alkalinity of the soil. It is measured on a scale that ranges from 0 to 14, where a pH of 7 is considered neutral, below 7 is acidic, and above 7 is alkaline.
Soil pH is determined by the concentration of hydrogen ions (H+) in the soil solution. Each step on the pH scale represents a ten-fold difference in hydrogen ion concentration.
Only a little bit out?
A solution with a pH of 3 has ten times more hydrogen ions than a solution with a pH of 4, and 100 times more hydrogen ions than a solution with a pH of 5. In practical terms, this means that small differences on the pH scale can result in dramatic differences in plant health
Why pH is important
pH is an essential factor for growing healthy plants as it influences the the availability of nutrients to plants, the activity of soil microorganisms, and the growth of plant roots.
African Violets grow best in a potting mix that is slightly acidic, with a pH between 6.0 and 7.0. Somewhere between 6.5 and 6.8 is considered ideal.
If the PH of your potting soil moves too far outside this optimal range, your plant will begin to deteriorate. For example, if the soil pH is too low, African violets may suffer from aluminum toxicity, which can inhibit root growth and nutrient uptake. On the other hand, if the soil pH is too high, African violets may not be able to absorb certain essential nutrients, such as iron and magnesium, which can cause yellowing between the veins of the leaves.
Why your plant's pH will change
Over time, the pH of your plant’s soil is likely to change for a variety of reasons, such as the type of mix, the frequency and quality of water used, and the use of fertilisers and additives.
The use of hard water for watering or the buildup of mineral salts in the soil can increase the pH level, making the soil more alkaline. Fertilizers that contain ammonium-based nitrogen sources can lower the pH of the potting mix, making it more acidic. On the other hand, fertilizers that contain nitrate-based nitrogen sources can increase the pH of the potting mix, making it more alkaline.
Peat moss, a key ingredient in many African Violet potting mixes, is naturally acidic (around 3.5 to 4.5). When making mix with peat moss, it’s important to buffer (alter) the pH using powdered lime stone. Over time, the buffering effect of the lime can wear off.
What to do about natural changes of pH
Symptoms of pH problems
The symptoms of pH problems vary depending on whether the pH is too high or too low. Also, on how far the pH is outside of the optimal range. Here are some general symptoms to look out for:
If the pH is too low (acidic soil):
- Stunted growth and small leaves
- Leaves turning yellow or brown
- Leaf edges and tips drying up or becoming brittle
- Slow development
- Reduced flowering or no flowering
If the pH is too high (alkaline soil):
- Leaves turning yellow or brown, especially around the edges
- Reduced flowering or no flowering
- Stunted growth
- Brittle leaves
- Loss of leaf color
When the soil is too acidic, the African violet may develop yellowing leaves. This is because acidic soil can interfere with the plant’s ability to absorb nutrients such as iron and magnesium.
African violets with soil pH problems can exhibit stunted or distorted growth. This is commonly confused as mite infestation
The edges of the African violet’s leaves may turn brown when the soil pH is too acidic. In extreme cases the crown will die. This is due to a buildup of salts in the soil that can occur when the pH is too low.
It is important to note that these symptoms can also be caused by other factors like overwatering, poor growing conditions, pests, and diseases. If your plant is showing any of these symptoms, you should test the pH of the mix to rule out pH as a contributing factor.
The pH of ALL new potting mix should also be tested. Don’t just assume that commercial mixes are ready to go. Recently, I tested the pH of two popular brands of commercial mix and both were significantly acidic, enough to potentially kill the plant.
3 tools for measuring the PH of your potting mix are electronic meters, soil test kits, and paper PH test strips
Digital PH Meter
Soil Test Kit (Wet)
Paper Test Strips
Taking pH sample of your plant
To take a pH sample of African violet mix, follow these steps:
- Water your African violet plant thoroughly, allowing the excess water to drain from the pot.
- Using a clean and sterilised tool, such as a small trowel or spoon, dig down into the soil mix to a depth of about 7-10 cm (3 – 4 inches). Take a small sample of soil mix from this depth, avoiding any roots or plant debris. Alternatively, tip your pot out and take a sample from somewhere in the middle of the pot.
- Place the soil sample in a clean container, such as a shot glass, plastic cup, or small bowl.
- Add enough distilled water to the sample to create a muddy consistency.
- Stir the soil and water mixture thoroughly to ensure that the water is evenly distributed.
- Allow the mixture to sit for a few minutes to settle.
- Dip a pH test strip or digital pH meter probe into the soil mixture.
- Follow the instructions for your test device to get an accurate pH reading of the African violet mix.
You should take multiple pH samples from different parts of the pot to get an accurate representation of the overall pH level of the soil mix. Additionally, make sure to clean and sterilize your tools and container before and after taking the samples to prevent contamination.
Treating a plant with pH problems
If you have tested your potting mix and found that it has pH problems, you have a few options: try and correct the Ph using soil additives, or repot the plant.
Adjust the pH level: If the soil is too acidic, add lime to the soil mix to raise the pH level. If the soil is too alkaline, add sulfur to the soil mix to lower the pH level. This option may require repeated testing to ensure you have achieved a reliable pH.
In general, your best course of action is to repot the plant in soil that is already stable and at the correct pH. When repotting, try to remove as much of the old mix from the roots. You could even wash the rootball in a bowl of tepid water.
The plants illustrated below were repotted 4 weeks ago due to pH problems and now show signs of new healthy growth.
To promote healthy growth, it is important to maintain the appropriate soil pH level for African violets. Gardeners can use pH testing kits to determine the soil pH and make necessary adjustments by adding appropriate soil amendments or fertilizers. By ensuring the correct pH level, African violets can thrive and produce beautiful blooms.