by Donaly W. Waikus

Editor’s note: The article below is a well considered response to the article, BROWN LEAF TIPS by Stephen Hendricks, which appears above. It originally appeared in the Fort Worth Bonsai Society NEWSLETTER Jan. 1994 pp 4-6

The addition of gypsum as a soil amendment to a potting mix, bonsai or otherwise, bears merit and should be considered. I have used many bags of gypsum on my Illinois lawn and garden to break up the clay, which was its big claim to fame, and I can heartily endorse its use.

The author of BROWN LEAF TIPS did considerable research into his unique problem and came up with a solution for that problem, and he is to be commended for his effort. However, as the scientific method for the testing was not contained in the text, it appears that there may have been other forces at work causing these problems rather than just the clay material. So, before you start dumping your "Turface" and "Solite" or adding any more amendments to your potting soil, here are some things to consider.

First, what was the pH of the soil after mixing, or was it even tested? Many plants thrive only when the pH of the soil closely approximates the optimum for that particular species. For example, azaleas do best in a range of 4.5 to 6.0; junipers want a range of 5.0 to 6.5; spruce want a range of 4.0 to 5.0. The greatest majority of plant life wants an acid condition, and if you are not sure of a particular species’ requirements, it is suggested that a pH of 6.5 is a good starting point.

Second, what was the pH of the water, its hardness and residual chemistry? Typical household water has a pH of about 7.6, with a chlorine residual of about 0.4 parts per million. Almost good enough to swim in, but not good enough for plants. I used to water my plants with aged household water, but not anymore. My well has a pH of about 6.0, with no chlorine residual, so that’s what I use on all my exotic tropicals, bonsai (including maples and azaleas, cacti and succulents. Many of these plants are over ten years old, and most have a minimum of 1/3 Solite in the soil mix. These plants show no signs of brown leaf tip from this soil mix or method of watering. The Japanese maples usually start showing some heat stress once the temperature gets to 85°F, and some tip burning is noted unless the plants are moved into some shade. The soil pH in the root zone of most of these plants is about 6.0.

Water hardness due to high levels of calcium, magnesium, etc., will leave deposits on your pots and soil. This is visible evidence that you may have a water problem. A simple pH test on your water source will tell you if you, indeed, have a problem. If your water is alkaline, the addition of vinegar is a simple, effective means of pH reduction.

If you have a brown leaf tip problem, and if you must use household water, put it into one gallon milk jugs or other such storage vessels and allow the water to age/stand for at least 24 hours before using it. This allows the chlorine and other gases to "burn off" or otherwise dissipate. This is what tropical fish hobbyists do, and it’s easier and cheaper than adding other chemicals to neutralize the chlorine.

It is not recommended that you use distilled water on your plants. Distilled water lacks the natural minor element chemistry necessary for growth. If you must use this as a water source, then it is suggested that you save the water from your dehumidifier or air conditioner and add the essential minors to that before watering your plants. It's certainly cheaper than buying bottled water.

I would not recommend the use of softened water on potted plants of any kind.

Third, variable pH in azalea pots? While azaleas may "prefer" deeper pots, so would most any other plant. Azaleas dislike dryness, and a deeper pot holds moisture longer. Plants that flower always have a greater affinity for water, and most flowering plants are usually placed into a glazed pot. I’m not so sure that "azaleas prefer a deeper pot" is an accurate rationale.

However, in the matter of greater acidity toward the bottom of the potting soil and not being aware of the method or amount of testing done by the author of the BROWN LEAF TIPS article, it would more likely be due to the pH of the water source and perhaps the original pH of the potting soil he used. It only stands to reason that if you started with a soil pH of 6.0, add water of the same value and use no other materials to affect pH, that the pH cannot change. You might get slight variations from test zone to test zone, but not enough to draw a conclusion that the depth of the pot can influence pH.

I have done some pH sampling on a number of potted plants, both shallow and deep. The pot depths varied from two to eight inches. The pH of the soil initially ranges from 6.5 to 6.8. The water source pH ranges from 6.0 to 6.2. The tested pH in the root zone of all the tested plants was in each case 6.0 plus or minus a couple of points for meter and reading accuracy. I did find that if the moisture content of the soil was less than half of the full scale moisture meter reading, that the test meter registered a higher pH. When the plant was thoroughly watered, the pH readings were fairly consistent throughout the entire pot. Consequently, I have determined that the pH meter needs considerable moisture to operate effectively.