Water is water, right? Wrong. The quality of the water used to grow marijuana can either help your plants thrive or spell disaster for your garden. This is basic stuff you need to know if you want to be successful at growing marijuana.
Water, or H2O, by itself is only that: 2 parts hydrogen and 1 part oxygen. Marijuana plants love the stuff, but we rarely find water that pure. Impurities dissolved or suspended in the water can either help or hinder in growing marijuana. Knowing what’s up with your water and what to do to correct a problem is pretty simple but you need to know the basics first.
TDS and EC
As I mentioned, water is rarely pure. Groundwater picks up minerals as it travels through earth and stone. Bottled drinking water has added minerals for flavor, while municipal water sources often add everything from chlorine to fluoride. Total Dissolved Solids (TDS) is the amount of these solids dissolved in the water or any other solution that can’t be removed with a standard filter.
As you may know, pure water does not conduct electricity. Because of this you can determine how much mineral or organic content is in the water by how well it conducts electricity. Electrical Conductivity (EC) is the measure of a solution’s ability to conduct an electrical current. TDS/EC meters have two electrodes that, when placed in the water or nutrient solution, pass AC voltage between them. The amount of current that passes through the solution indicates the conductivity of the solution. The meter reads this current and converts it to a display that will allow you to either read the EC or TDS (parts per million, ppm) of the water or solution.
By determining the baseline TDS of your fresh water you can later determine the strength of the nutrient solution you are going to mix. For example, if your tap water starts with a TDS of 600 ppm, and your fertilizer of choice suggests a dosage strength of 1200 ppm, you will know that the total TDS should come out to 1800 ppm. If you didn’t know the baseline, you might stop at a TDS of 1200 ppm and, by doing so, give your marijuana plants only half of the required nutrients.
Unfortunately without having your water tested or getting a report from your municipal water supplier, you won’t know the makeup of the minerals dissolved in that baseline TDS. For those growing marijuana indoors, there is an economical solution. Small reverse osmosis systems can remove nearly all of the dissolved solids from your water, bringing the TDS to nearly 0 ppm. You will then need to add back in the trace elements like calcium and magnesium required by marijuana plants, but can do so in the exact amounts needed.
The pH (potential of Hydrogen) of your water or any other solution is the measure of its acid or alkali levels. When a solution has equal levels of acid and alkali molecules, then the solution is pH neutral. The pH scale runs from 0.0 to 14.0 where 7.0 is neutral, less than 7.0 is acidic, and levels above 7.0 are alkaline or base/basic solutions. Depending on the growing medium used, you want to stay in the slightly acidic range of 5.5 to 6.5. To keep your growing medium and root zone at the correct pH, you need to keep the water or nutrient solution you are using at the correct pH. Contaminants in the water — whether naturally occurring, added by your municipal water supplier, or added when you mix in nutrients and fertilizers – will all affect the pH and may need to be corrected.
You might remember measuring acidity using litmus test strips in high school science or before adding chlorine to a hot tub. While comparing colors can be fun, it’s just not as accurate as you need to be for growing marijuana. To accurately measure the pH of your water or nutrient solution, you are going to need a pH meter.
If your pH doesn’t stay in the safe zone of 5.5 to 6.5, your marijuana plants won’t be able to absorb all of the necessary nutrients, which will lead to nutrient deficiencies. Because nutrient deficiencies can ruin a garden, a quality pH meter is one of the most important tools you will use for growing marijuana. When growing marijuana indoors, you’ll be testing your nutrient reservoir almost every day. If you are growing marijuana outdoors, a pH meter won’t be used as often but is still an essential tool. Luckily pH meters are relatively inexpensive. While options abound, pH meters by Hanna Instruments are the only meters I personally trust.
When growing marijuana, its best to keep the water temperature about 70 degrees Fahrenheit. Below about 65 the roots have more trouble taking up water and nutrients, while above about 78 can be equally detrimental to the roots. If your nutrient reservoir is located in your indoor grow room, it will probably hold a temperature in this range as it adjusts to the ambient temperature of the room. You should test the water temperature daily with a reservoir thermometer just in case. If you find that the water is staying too cool or that a fresh reservoir takes too long to reach the desired temperature, a reservoir tank heater and thermostat will do the trick. If the reservoir is getting too warm, you have a few solutions. First, if possible, try moving the reservoir out from under the grow light. Just like a water bottle left in the car, the container and water will quickly absorb the heat if left exposed to direct light. Try moving it under a tray table or otherwise creating some shade. If all else fails, try moving the reservoir out of the room entirely.
Aerating Your Reservoir
Roots love oxygen and oxygen-creating movement in water slows the growth of algae. By adding air to your reservoir you can kill two birds with one stone. A small reservoir aeration compressor and air stone similar to what is used in aquariums can be used to aerate the solution of water and fertilizer. This allows you to deliver oxygen to the root zone where it is needed most. Additionally, as the bubbles float to the surface of the tank, the moving air will help stir the reservoir slowing the growth of algae.
Water Quality and Growing Marijuana,