by George Buehler

A while back I was looking for something educational to print in the newsletter when I ran across a table of pH ranges for various tree types (See page 5). I put the table in a folder for further research and the eventual article to put in this newsletter. I had forgotten about it until an insert in one of our water bills recently, showed the quality of the water in Louisville. Looking for a little more information than was included in the insert, I went to the water company's web page. Among other things, I found that the average pH of Louisville water is 8.2. Therefore, if you use Louisville water, you are making your pines basic every time you water.

We have heard that pines and junipers like an acidic soil. But, based on the table on page 5, azaleas needs a slightly more acidic soil than a pine - by about 2.5 times. An Oak requires more acidic soil than a juniper- by about 5 times. I calculated this from the pH ranges listed on page 5.

But, before we go on, let's discuss what pH is. I promise we won't get too technical, but we must delve into some technicalities to help you get a better understanding. I will also be making some statements below without going into the chemical reactions that are involved to try to keep the article simple.

The term "pH" was invented in 1909 by the Danish chemist Søren Sørensen. pH was originally written by Dr Sørensen as PH, and it stands for pondus hydrogenii which means "potential hydrogen". The terminology refers to acidity being due to a predominance of hydrogen ions in an aqueous (water containing) solution. In plain English, pH is a measure of a water solution's acidity.

For simplicity, the strength of an acid or base in a solution is measured on a scale called a pH scale - it can be calculated mathematically, but that is way beyond the scope of this article. When a solution is neutral (i.e. neither acidic nor basic), it has a pH reading of 7. Distilled water - water that has been turned to steam then recollected as liquid water to remove the salts in the water - has a reading just about 7. If a solution has a reading higher than 7 it is considered basic and, likewise, solutions with a pH lower than 7 are acidic. 0 (bottom of the pH scale) is the strongest acid, and 14 (top of the pH scale) is the strongest base. The only other important thing to know about the pH scale is that it is logarithmic. That is, each whole unit on the pH scale is a tenfold increase or decrease in strength. A pH shift from 6 to 7 represents a 10-fold decrease in hydrogen ions (7 is 10 times less acidic than 6), while a shift from 6 to 8 represents a one hundred fold decrease in hydrogen ions. That is why an azalea with a pH range of 5 to 6 (average 5.5 pH), is 2.5 times more acidic than a pH of a pine with a pH range of 5.5 to 6 (average of 5.75).

As stated above, Louisville water has an average pH of 8.2. I asked one of the technical experts at the Louisville water company why the reading was not closer to 7 (neutral). She said that it is due to the limestone we have in this area. The rain we get is slightly acidic (less than 7 pH). As the water goes into the ground, it runs over the limestone and dissolves it, causing the pH of the ground water to rise - increasing the amount of calcium carbonate in the water. Indianapolis has a reported average pH of 7.25, and Nashville reported an average pH of 7.0 (ranged from 6.5 to 8.5 during 2005). When asked why they didn't remove some of the entrained calcium salts, the reply was that it would be too expensive. Another reason Louisville Water Company and several other municipal water companies keep the value slightly high is because when the water is acidic, it will dissolve out some of the lead in the solder used to hold the pipes together, and lead is a known carcinogen. Therefore there is also a safety reason.

Most plants grow best in a slightly acid to neutral soil (pH of 6 to 7). Actually a pH of 6.5 has been shown to be the point where minerals become most available to plants. As an example, nitrogen, phosphorous, potassium (NPK), and trace elements are most readably accessible at a 6.5 pH. Therefore, if your bonsai soil is either too acidic (low pH) or too basic (high pH), the trees ability to adsorb nutrients will be diminished. Aluminum, iron, and manganese precipitate in high (basic) soils ,and plants in a high pH soil may show signs of deficiencies of Iron, boron, zinc, and several other micronutrients. If a tree is showing signs of these deficiencies, simply adjusting the pH will generally correct the problem in a short time.

We water daily in the summer, and we are using water with a pH of 8.2. Is this affecting our trees? It appears that a lot has to do with the amount of rain received, the amount of acidic materials used in your soil mix - like peat or pine bark, the specific type of components in the soil, or whether you use an acidic type fertilizer.

Some of the minerals in the water are adsorbed by the plant. However not all, and those remaining minerals are either deposited into the soil as the water is used or they are flushed out with the daily watering routine. Over time, the pH of the soil in our pots should gradually creep up the pH scale or become more basic. But does that really happen? Probably to some extent, but, because the soil is changed routinely, it probably doesn't make much difference. If a tree is not re potted for a number of years, the basic build up may become important. Use of an acidic fertilizer or a soil amendment chemical (see below) should also take care of any problem.

In the Ohio Valley, the summer rain is normally slightly acidic due to the pollution we have in the area. If we receive any rain, and there has been some deposition of minerals, the acid rain water will most likely re-dissolve some of the deposited minerals, and they will be partially flushed out of the soil. Therefore, if we have a normal amount of rain, any deposition of minerals will be taken care of.

If you use an acidic soil like Kanuma or add an acidic component (like peat or pine bark), the basic tap water is always coming in contact with these acidic components then a chemical reaction takes place, either neutralizing the water solution (moving the pH toward 7) or lowering the pH of the entrained water. This reaction continues to take place as long as there are acidic sites available in the soil.

All commercial container growers routinely monitor their soil several times during the growing season. One of the procedures used is called the VTEM method (stands for Virginia Tech Extraction Method). This method calls for wetting the potting media with distilled water, then adding additional distilled water while collecting a fixed amount of the effluent water, and measuring its pH. They then add chemicals to their watering system to bring the soil pH into the range they need for the particular plants they are growing.

For the typical bonsai artist, this method would be entirely too complicated since it would require a pH meter (expensive) and, there are a number of species with differing pH requirements. So what is the bonsai artist to do? The pH could be adjusted by adding an acidic fertilizer like MirAcid, but, at this time of year, we don't want to add high nitrogen fertilizers since that would cause rapid new growth. A small amount of powdered aluminum sulphate can be sprinkled on top of the soil to make the soil more acidic. Since this material has little nutrient value, it can be safely used, as long as it is added in small quantities.

If we look at the soil composition, most bonsai soils contain some sort of calcined clay aggregate such as Haydite. These clay materials absorb and hold salt ions (components of chemicals like sodium or calcium). These ions are adsorbed on the surface of the clays to form a concentrated salt region where the roots grow. Of course, calcium is a needed component for good plant health and growth. However, when trees like a Japanese maple is exposed to a high salt content, the result is the typical leaf burn we see in mid-summer and blame on the sun. However, the leaf burn may be due to the high salt concentration in the margins of the leaves. Once again, use of an acidic component in the soil would help alleviate this salt build-up. An additional corrective action would be to substitute the clay for a sand type component or decomposed granite in the next replanting.

The bottom line to using the high pH Louisville water is that a number of things we routinely do in the maintenance of our trees take care of any potential problems. In looking at the quality of our water, it is substantially better than that used in other areas of the country. If you are having problems with the health of your trees due to the pH, there are a number of things that can be done to help this situation. Looking at the pH table should give you a better idea of what various trees require.