Potting Soil - pH Imbalance

Description

pH is short for puissance de hydrogen and refers to the measure of acidity or alkalinity of any substance. A pH below 7.0 is considered acidic, while a pH above 7.0 is alkaline. Correct soil pH is vital for the health and performance of African Violets. Optimum soil pH ranges from 5.8 and 6.2. A good potting soil, which has been blended especially for African Violets, will have the correct pH. However, there are other factors which can affect pH, such as concentrations of fertilizer salts and soft water. If the pH of the potting soil varies too much from 5.8 to 6.2, your African Violet will not be able to absorb the proper amount of nutrients it needs. For instance, high pH can result in a decifiency of iron, whereas low pH can result in a deficiency in phosphorus.

Distinguishing Symptoms

Due to the complex interaction between the soil pH and plant nutrients, it will be difficult for most to distinguish symptoms arising from a pH imbalance from those due to a simple lack of available nutrients. However, there is at least one instance when you can be certain that a pH imbalance is playing a role. If you are using soft water to water your Violet, it is almost certainly suffering from a pH imbalance in the soil. Aside from this, and short of sending your Violet to a laboratory for testing, you will probably have to be satisfied with the knowledge that your Violet is suffering from a lack of nutrients, whether or not it is caused by a pH imbalance in the soil. This said, do not be discouraged. Regardless of the cause, the problem can be successfully treated. (See below.)

Other Symptoms

Listed below are some of the symptoms you may encounter from a pH imbalance in the soil. Accompanying these symptoms are some of the specific elements which your Violet may be unable to absorb due to a pH imbalance.

• Leaves pale between the veins. This is a condition called interveinal chlorosis. Chlorotic areas appear yellow in color. This symptom is most likely due to your Violet's inability to absorb either iron, magnesium or manganese.
• Leaves pale on the edge. Edges appear yellow in color. This condition is called "halo-ing" and will probably be the earliest sign that a pH imbalance is at work.
• Leaves pale only on the tip. Tips appear yellow in color. This symptom is most likely due to your Violet's inability to absorb either copper, magnesium or manganese.
• Leaves pale. As the pH imbalance continues, you may see entire leaves turning yellow.
• Leaves pale only in the crown. This is probably due to your Violet's inability to absorb calcium.
• Leaves have yellow spots on them. In cases of a pH imbalance in the soil, this symptom is likely due to your Violet's inability to absorb boron.
• Leaves have white spots on them. When your Violet is unable to absorb copper, you may see this symptom, especially in the new growth, i.e., in the crown.
• Leaves have brown spots on them. This symptom is most likely due to your Violet's inability to absorb manganese.
• Leaves darken on the edge. Edges appear brown in color. This is necrosis, where leaf tissue is actually dying. This symptom is probably associated with a lack of molybdenum.
• Leaves darken. Entire leaves appear brown or black in color (necrosis), especially in the new growth, i.e., in the crown. This is probably due to your Violet's inability to absorb copper.
• Leaves are deformed or twisted. This symptom will be most visible on the younger, smaller leaves of the crown and is probably the result of your Violet's inability to absorb boron, calcium, copper or zinc.
• Leaves curl up on the edge. This is probably the result of your Violet's inability to absorb potassium.
• Leaves are brittle or cracked. This symptom is likely due to your Violet's inability to absorb boron.
• Leaves are smaller than normal. This symptom will arise most often as a result of the Violet's inability to absorb nitrogen. However, if this symptom appears predominantly in the crown, then it may be the result of your Violet's inability to absorb zinc.
• Leaves drop. This is probably the result of your Violet's inability to absorb manganese, phosphorus or zinc.
• Leaves turn purple on the underside of them. This symptom will be most common on varieties which have red reverse leaves, especially during cooler weather. Be sure not to confuse this symptom with the dark red or purple reverse leaves which are characteristic of some varieties.
• Buds do not open. This is probably the result of your Violet's inability to absorb calcium.
• Not flowering. If your Violet is not flowering, it is probably unable to absorb phosphorus.
• Flowers drop off. This symptom is likely due to your Violet's inability to absorb boron.
• Flowers changing color from purple to red (or red to purple). Anthocyanin, the pigment which produces the purple color in Violets, is very sensitive to changes in pH. As a result, repotting or changing fertilizers can cause certain purple or purplish-red varieties to become lighter or darker.
• Crown pales. This is probably due to your Violet's inability to absorb calcium.
• Crown darkens. It appears brown or black in color. This is probably due to your Violet's inability to absorb copper.
• Crown deformed. This symptom is probably the result of your Violet's inability to absorb boron, calcium or copper.
• Plant growth is slow.

Treatment

Assuming that you have ruled out other possible causes for the symptoms you are encountering, your best course of action assumes that your Violet is suffering from a general lack of nutrients and that a pH imbalance in the soil may or may not be the cause of it. With this in mind, here is what you should do.

First, repot your Violet with fresh potting soil. After separating the rootball from its container, shake as much of the old soil from the roots as you can without disturbing the roots too much. Repot the plant in a potting soil that is light, porous and guarantees a pH of 5.8 to 6.2.

Next, drench the soil with lukewarm water. Water from the top until about a cup (8 oz.) of water has drained from the pot. Allow any excess water to drain. This will help leach out any of the substances that may have contributed to a pH imbalance. If these substances were the cause of the problem, they may still be present in the old soil that clung to your Violet's roots.

After you have drenched the soil, wait one week. During this time, do not use a fertilizer. The nutrients in the soil will be sufficient until you begin fertilizing again.

After one week, you may notice that your Violet has already begun to recover. If it has, it was most likely suffering from a pH imbalance in the soil. In either case, you can again start fertilizing. When selecting a fertilizer, be sure that it contains approximately equal amounts of the primary nutrients, nitrogen (N), phosphorus (P) and potassium (K). For standard-sized African Violets (in 3-inch pots or larger), an NPK of 14-12-14 is recommended. For Miniature Violets, you will need a fertilizer specifically formulated for miniature plants, such as Optimara Miniature Plant Food. In addition to being fully-dissolving, make sure that the nitrogen is not derived from urea, since urea will cause Root Burn on African Violets. Sources for each of the three primary elements can be found in the Guaranteed Analysis, located on the fertilizer label. (Note: Many of the micronutrients, though essential to the health of African Violets, are often not listed on the Guaranteed Analysis. If interested, reputable Violet Food producers will generally be happy to send you a complete analysis upon request.)

Important: If symptoms begin to return, you may have a problem with your water. Some common problems with water include too much chlorine in the water, too much boron in the water and soft water. If you suspect your water to be the problem, repeat the above steps and try using non-distilled, bottled spring water on your plants. If symptoms clear up, your water is almost certainly the problem. To be sure, you may want to have a sample of your water tested at a laboratory. If you do, have them check the levels of boron, zinc, molybdenum, potassium and chlorine. These are the most likely causes of problems for plants.

Prevention

Use a recommended Violet Food or fertilizer specifically formulated for African Violets. Your Violet Food should be fully-dissolving and contain approximately equal amounts of the primary nutrients, nitrogen (N), phosphorus (P) and potassium (K). Miniature Violets generally need a slightly higher proportion of phosphorus, such as that contained in a 7-9-5 formula. Also, your Violet Food should not contain urea nitrogen, since urea causes Root Burn on African Violets.

Use a potting soil that is light, porous and guarantees a pH of 5.8 to 6.2. For best results, your potting soil will consist of mostly block-harvested, sphagnum peat moss. Other ingredients may be included to increase the porosity and stabilize the pH.

At least twice a year, repot your African Violet, using fresh potting soil.

About every three months, drench soil with lukewarm water to leach out any unwanted concentrations of fertilizer salts. To do this, water from the top until about a cup (8 oz.) of water has drained from the pot. Allow any excess water to drain.

Do not use soft water. Soft water increases the saline content in your potting soil. This will alter both the pH and the electrical conductivity of the soil, thereby affecting an African Violet's ability to absorb water and nutrients.

Finally, if the pH of your potting soil is a recurring concern, you may want to measure the pH from time to time. Reasonably inexpensive pH test kits are available at most garden centers. For African Violets, the pH should measure between 5.8 and 6.2.

For more about potting soils, pH and the proper absorption of nutrients, see "Caring for African Violets."

Begin New Diagnosis

Doctor Optimara Main Page | Glossary of Violet Terms | Contact Optimara

Pests, Pathogens and Cultural Problems (Complete List)

Copyright 1999 Optimara/Holtkamp Greenhouses, Inc. Nashville, Tennessee. Doctor Optimara is a trademark of Holtkamp Greenhouses, Inc. Optimara and the Optimara logo are trademarks of International Plant Breeding, A.G., Switzerland.