Water and pH
learn How pH Affects Orchids
Water quality is one of the key components of successful orchid growing, and yet many discussions of the issue become very technical very quickly and become virtually incomprehensible. We're going to try here to discuss the issue of water without delving too deeply into the science behind it. First off, there are 4 types of water in general use: rain, RO, tap, and well. We'll discuss each separately as they each present their own unique issues and challenges to the orchid hobbyist. The simplest water to understand is pure water, in the form of rain water or reverse osmosis (RO) water. Water that comes from the municipal water supply, tap water, and well water will have many different dissolved solids and chemicals in it.
The quality of water has a direct relationship with the quality of the fertilizing solution we use on our orchids. We mix fertilizer and water and hope to feed the plants. Unfortunately, if the pH is too high or too low, the orchids will not be able to consume all the nutrients we are giving them in the fertilizer. This can result in nutrient deficiencies even as we are pouring nutrients on the plants! The type of water and the type of fertilizer both have an effect on the pH of the resulting fertilizer and water solution. By far the simplest thing to do is to test the pH of the fertilizing solution. You can get a pH meter but unfortunately those require calibration to be certain the results are accurate. The simplest way to test pH is with pH test strips, simple, accurate, low cost with no calibration required.
There are two primary factors at play when it comes to pH, the pH of the fertilizing solution and the pH of the orchid mix. Once orchid mix has been in a pot with an orchid for a while there is a lot happening that can have an effect on the pH of the orchid mix. The orchid mix breaks down over time and has fertilizer and water added to it which have their own pH and that leave behind residue. There are several good methods for testing the pH of the orchid mix and commercial growers of all types of crops, not just orchids, typically will test the pH of the mix in the pot every few weeks. One method we are particularly fond of is the "pour-thru" method, since it does not involve disturbing tender orchid roots. About an hour after orchids have been watered, take a plant and pour RO water (or distilled water) through it until a couple of ounces come out the bottom of the pot. This water, called the "leachate" is then tested for pH using a pH test strip.
At the end of the day, it makes sense to keep both the pH of the fertilizing solution and the pH of the orchid mix within the optimal range for nutrient absorption. For most orchids we recommend a pH between 5.5 and 6.0. To lower pH, use Citric Acid. To raise pH use Lime or Oyster Shell. If the orchid mix pH is too high, micronutrient deficiency can occur. Conversely, if the pH of the orchid mix becomes too low, micronutrient toxicity can occur.
Rain water is what orchids receive in their natural environment. It is a form of pure water in that it has no dissolved solids. Because it has no dissolved solids, it doesn't have anything to "buffer" the effect of fertilizer added to it. This is why when rain water is used with orchids it is very important to use a fertilizer designed for use with pure water such as our FEED ME! MSU Orchid Fertilizer. Fertilizers that contain Urea as a nitrogen source when used with pure water will become too acidic and will tend to drive the pH of the orchid mix down.
Reverse Osmosis (RO) Water
Reverse Osmosis is a form of water purification which removes dissolved solids from water. Because it has no dissolved solids, it doesn't have anything to "buffer" the effect of fertilizer added to it. Our FEED ME! MSU Orchid Fertilizer is the original fertilizer that was used by Michigan State University in the study of orchid fertilizers. RO water is a form of pure water just like rain water. Fertilizers that contain Urea as a nitrogen source when used with pure water will become too acidic and will tend to drive the orchid mix down.
Tap water varies greatly across the United States and the world. In some states the tap water is pretty good, low in dissolved solids and quite suitable for use with orchids. In many states, however, tap water has too many dissolved solids. One advantage with municipal water is that many water companies must publish their water quality reports online. Ours is online, our water comes from the Potomac river. In looking at this report we can see that our tap water tends to be hard, it has 120-130 PPM of solids, while our neighbors to the east get the less hard Patuxent water that is softer, around 60-65 PPM. When we measure our tap water it varies from day to day and goes as low as 100 PPM and as high as 200 PPM. As a general rule of thumb water that has less than 100 ppm of solids is good. If water is too hard, one way to reduce the effective hardness of the water is to add Citric Acid. Tap water also may contain high levels of fluoride and chlorine. Levels above 1 PPM are too much and in the case of chlorine, levels above 1 PPM are commonplace. From our water report we can see that our water contains acceptable levels of fluoride but not of chlorine. Luckily Chlorine will evaporate over time or can be removed with a filter. This is why many folks choose to fill their watering containers and then let them sit for a day before using the water on the orchids. The accomplishes two goals, the chlorine evaporates and the water reaches room temperature.
The chemical composition of well water is unique to the well it is drawn from. In order to determine what is in well water, it should be tested before being used on orchids. Once the makeup of the water is understood, the same rules as tap water apply.