Marijuana
pH And Marijuana (Cannabis)
pH is measured on a scale from 0.0 to 14.0. Pure water has a pH of 7.0 and is considered pH neutral. pH below 7.0 is considered to be acidic and pH higher than 7.0 is considered to be alkaline.
A substance that decreases pH (pH-down) is called an acid while a substance that increases pH (pH-up) is called a base. A substance that helps resist pH changes when an acid or base is added, is called a buffer.
A pH difference of 1.0 is equal to a ten times increase or decrease in pH. That is, a nutrient solution with a pH of 6.0 is ten times more acidic as a nutrient solution with a pH of 7.0. A pH difference of 2.0 is equal to a hundred times increase or decrease in pH.
It is very important to keep the pH level within certain limits when growing marijuana. Even first time marijuana growers need to monitor the pH of their nutrient solution or soil and keep it within a certain range.
The pH level of your hydroponic nutrient solution or soil will determine how well your plants are able to absorb nutrients. If the pH level is out of the proper range, the growth rate of the plants will slow down or stop.
Temperature, nutrient, and pH problems are the top three things that cause a crop failure when growing marijuana. By monitoring and keeping them within optimal ranges you will maximize the chances of a successful crop.
Checking The pH Level Of Marijuana
There are several options when it comes to checking the pH level of your hydroponic or soil garden:
--- A pH Control Kit that contains a pH test kit to measure the pH of liquids like water or hydroponic nutrient solution, pH-up to raise the pH, and pH-down to lower the pH.
--- A pH Test Kit is used to measure the pH of liquids like water or hydroponic nutrient solution.
--- A pH Meter is used to measure the pH of water and other liquids, hydroponic nutrient solution, hydroponic media, etc. Get a pH meter intended for liquids with a hydroponic garden. Some pH meters are strictly to measure soil pH.
--- A Soil Test Kit is used to measure the pH, nitrogen, phosphorus and potassium levels of soil. There are also soil pH test kits available that just measure the pH level of soil.
--- A Soil pH Meter is used to measure the pH of soil.
First time hydroponic marijuana growers should consider getting a pH control kit that contains everything you need to monitor and adjust pH. Look for a control kit that includes a pH test kit to measure the pH level, and pH-up and pH-down to adjust the pH.
A pH test kit for liquids works by putting a small amount of nutrient solution in a container then adding a few drops of pH test liquid and mixing them together.
The combined mixture will turn color. This color is then matched with the color on a pH chart (included with the test kit) to determine the pH level of the nutrient solution.
A pH meter can measure the pH of water (and other liquids), hydroponic nutrient solution, hydroponic media, etc. If you have been growing hydroponic marijuana for a few years and you are tired of buying and re-buying test kits, it might be best to invest in a pH meter.
A pH meter for liquid measurements is long lasting, and will give more accurate results than other methods of measuring pH. But the price may make them out of reach for first time growers on a budget. pH meter probes and batteries will also eventually need to be replaced.
Besides the pH meter itself, you also need to purchase pH calibration solution to ensure accurate readings and electrode storage solution to extend electrode life. To save money look for a pH calibration kit that includes storage solution as well as calibration solution rated at about 4.0 and 7.0.
Calibrating the meter is especially important because all measurements will be wrong if the unit is mis-calibrated. Most kits include 4.0, 7.0, and 10.0 calibration solutions but it is not necessary to calibrate the meter with 10.0 when growing marijuana. If the pH is not within 4.0 to 7.0, your plants will die.
Soil growers should get a soil pH meter to measure the pH level of soil in their garden. They work by inserting the probes of the unit directly into the soil you are growing in, and taking a reading. Follow the manufacturers instructions included with the soil pH meter you have, and you will get years of accurate measurements.
An alternative for soil growers is a soil test kit. These are easy to use and reliable kits that contain separate tests for pH, nitrogen, phosphorus, and potassium. They give instant results on the soil conditions in your garden.
A single soil test kit will have a certain number of tests that can be preformed before you run out and have to buy another. For example, one company makes a soil test kit that can be used to check pH, nitrogen, phosphorus, and potassium levels in soil 10 times.
pH And Hydroponic Marijuana
When growing hydroponic marijuana the pH of the nutrient solution should be between 5.5 and 6.5. In most cases optimal pH for marijuana plants is about 5.8 to 6.2 but this may vary slightly depending on the particular marijuana strain and the growing conditions you provide.
Some growers report good results with pH as low as 5.0 but you should try to maintain 5.8 to 6.2 pH readings for your first few crops. When you gain experience with a particular marijuana strain, you can experiment with pH and see what works best. However, you must always make sure to keep the pH between 5.0 and 7.0.
When rockwool is employed as media, the pH of the nutrient solution has to be lowered so it stays between 5.1 and 6.1. An optimal pH for hydroponic marijuana plants grown in rockwool is about 5.6 to 6.0.
This is because rockwool contains lime. The lime raises the pH level the roots are exposed to, so always keep pH lower than 6.1 with rockwool. If the pH goes over 6.1 plants grown in rockwool will slow or stop growing.
Note that prior to use, rockwool should be washed by soaking in water that has a pH of 5.0 to 5.2 for 24 hours. After that it should be rinsed in water that contains nutrients. Adjust the rinse to a similar level of nutrients and pH to those the rockwool will be placed in when growing.
After the rockwool has been washed for 24 hours, rinse it by soaking in the pH adjusted nutrient solution for 30 minutes or longer and it is ready for marijuana to grow in. Discard the liquid that the rockwool was washed and rinsed in when finished.
Measure the pH after you add the nutrient solution to the reservoir, mix well first because the nutrients will change the pH level of the water. In almost all cases nutrients will lower the pH of water. When you first start growing, check the pH everyday (or several times a day) and make sure it is within the proper range.
Adjusting pH Of Hydroponic Marijuana
pH-up and pH-down solutions are used to adjust the pH level of hydroponic nutrient solution and hydroponic media when the pH is out of range.
pH-up (also called pH increase) is used to raise the pH level and pH-down (also called pH decrease) is used to reduce the pH level. A pH-up or pH-down solution for hydroponic or aquarium use is recommended.
For hydroponic applications, nitric, phosphoric or citric acids (even vinegar) can be used to lower pH, while potassium hydroxide can be used to raise pH.
If you understand what you are doing, you can use these various chemicals instead of buying pH-up and pH-down solutions (contributed by james and jorge).
However, if you aren't sure of the correct amount of acid or base that is needed to adjust the pH to optimum values, it is best to buy a solution specifically made to raise or lower the pH and carefully follow the manufacturers instructions.
Unless directed to do so by the manufacturer, don't try to adjust your nutrient pH by more than 1.0 per day. Always make drastic changes over a number of days. Plants need a gradual change, overcompensating can kill your plants.
pH, Water, And Hydroponic Marijuana
Depending on your source of water, the nutrient solution in your hydroponic set up may or may not offer any buffering ability. A substance that helps resist pH changes when an acid or base is added, is called a buffer.
Tap or well water that is considered hard water often contains levels of calcium and magnesium that have good buffering ability. Reverse osmosis, distilled, and tap or well water that is considered soft water contain levels of calcium and magnesium that offer very little to no buffering ability.
Adding a small amount of an acid or base to water with little buffering ability will cause a major change in pH. If you notice that your pH level changes drastically when nutrients or pH up/down are added, a calcium/magnesium supplement will probably help.
For example, my 3.5 gallon cloner with reverse osmosis water will go from a pH of 5.9 to 5.8 when a single drop of pH-down is added. If the same 3.5 gallon cloner has reverse osmosis water that is buffered with a calcium/magnesium supplement, to go from a pH of 5.9 to 5.8 it takes about 5 drops of pH-down.
When buffering water for use in a hydroponic system with a calcium/magnesium supplement, Botanicare Cal-Mag Plus is recommended. Do not use General Organics CaMg+ in hydroponic applications. Growers (including myself) have had problems with a foul smelling foam forming in the reservoir.
In addition, the pH level rises to dangerous levels quickly and can not be kept in check. This problem is most common in deep water culture systems but similar problems have been reported with ebb and flow, as well as other types of hydroponic systems.
pH And Marijuana Grown In Soil
When growing marijuana in soil the pH of the soil should be between 5.5 and 6.5. An optimal pH level for most types of soil is somewhere between 6.0 and 6.3. When growing in containers, a single pH reading for each container is recommended.
When growing outdoors in a large garden, it is best to take several pH measurements from different areas of the garden. You may have to adjust the pH in various parts of your garden by different amounts. Once stabilized and plants have started growing, check the pH at least once every one-two weeks.
Most fertilizers cause a pH change in the soil. Adding fertilizer to the soil almost always results in a more acidic (lower) pH. As time goes on, the amount of salts produced by the breakdown of fertilizers in the soil causes the soil to become increasingly acidic and eventually the concentration of these salts in the soil can cause browning of the foliage and stunt growth.
Adjusting pH Of Marijuana Grown In Soil
It is important to start plants in soil that is pH ready, rather than trying to drastically adjust pH levels after planting. Small adjustments to the soil where plants are growing is fine, but make sure the pH is in range and stable prior to planting.
Outdoors large growing areas with acidic soils can be treated with limestone or an additive that contains lime to raise the pH level. Dolomite lime (calcium-magnesium carbonate) is good for raising both the pH and magnesium levels of soil.
The finer the size of lime particles gets, the quicker it will affect a soil. Coarser grades can take a year or longer to work while finer grades work more quickly.
Alkaline soils can be treated with sulfate or magnesium sulfate to lower the pH level. Magnesium sulfate is good for lowering the pH and raising the magnesium levels in soil.
After treating an outdoor growing area by working the pH adjustment material into the top 1-2 inches of soil, water the treated area well.
Instead of planting right away, wait 4-5 months before taking final measurements and growing there. This is to allow the soil enough time to mix and stabilize.
When growing in containers besides the methods described above, small amounts of hardwood ashes will raise pH quickly while dry powered (in a blender) seashells or egg shells will gradually raise the soil pH. Small amounts cottonseed meal, citrus fruit rinds or coffee grounds will lower the pH of soil.
Wait at least a day or two before checking the pH level of soil in containers after attempting to raise, lower or stabilize it. If adjustments still have to be made, use small amounts of whatever material you are using.
When watering plants that are growing in soil, if the pH of the water itself is not in the proper range, pH-up or pH-down (employed to raise or lower the pH of hydroponic nutrient solution) can be mixed with the water to achieve an optimal pH level.
Related Books Marijuana Grower's Handbook
Very comprehensive book by Ed Rosenthal that covers all aspects of indoor and outdoor marijuana cultivation with soil and hydroponics. A reference manual with over 500 pages and color images throughout.
The water section of the book explains pH, and other information that would apply to hydroponic growers. The section about soil includes info on pH and soil, adjusting pH of soil, soil testing, types of soil, containers, and more. Also explains soil and growing outdoors as well as potting mixtures for growing in containers (indoors and outdoors).
Marijuana Grower's Handbook
Marijuana Horticulture
By Jorge Cervantes, this is a very good book that includes information about growing marijuana inside and out with soil or hydroponic methods. A reference manual with over 500 pages and more than 1000 color images. Describes growing marijuana outdoors and indoors (with hydroponics or soil). Contains information about pH and hydroponics as well as pH and soil.
Marijuana Horticulture