pH is measured on a scale from 1.0 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 nutrient solutions 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 as 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 optimum levels.
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.
Checking The pH Level Of Marijuana
There are several means of checking the pH level of your hydroponic or soil garden. See
this for information about obtaining pH measuring and adjusting equipment.
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pH Meter: used to measure the pH of water, hydroponic nutrient solution, hydroponic media, and soil.
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pH Test Kit: used to measure the pH of liquids like water or hydroponic nutrient solution.
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Soil pH Meter: used to measure the pH of soil.
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Soil Test Kit: 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.
First time hydroponic marijuana growers should get a simple pH test kit to check pH levels. They are cheap, easy to use, and can be used multiple times. However, you will eventually run out of pH test liquid and have to buy a new kit.
They work 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 be used to measure the pH of water, hydroponic nutrient solution, hydroponic media, and soil. 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 is long lasting, and in general they 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. They also have probes and batteries that eventually will need to be replaced.
For accurate measurements always follow the manufactures instructions for calibrating, cleaning, and using a pH meter. Calibrating the meter is especially important because all measurements will be wrong if the unit is mis-calibrated.
Because pH meters can measure the pH of water, hydroponic nutrient solution, hydroponic media, and soil they are strongly recommended for growers who use hydroponics to grow indoors and soil to grow outdoors.
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 use, 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 6.8. In most cases optimal pH is about 5.8 to 6.3 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. You can experiment to see what works best for your particular plants but always keep the pH between 5.0 and 7.0.
Measure the pH right after you add the nutrient solution to the reservoir (mix well first) because the nutrients will change the pH level of the water. Check the pH level about once a week.
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 them 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 pH by more than 0.2 per day. Make drastic changes over a number of days. If your pH is 7.0 and you would like it at 6.5, try lowering it by 0.1 a day for 5 days (or do it even more gradually). Overcompensating can spell disaster for your garden.
pH And Marijuana Grown In Soil
When growing marijuana in soil the pH of the soil should be between 6.5 and 7.0. When growing in containers, a single pH reading for each container is recommended. When growing outdoors in a garden, it is best to take two or three pH measurements from different areas of the garden.
If you have a large garden, you may have to adjust the pH in various parts of your garden to different levels. Check the pH once every one-two weeks.
Unlike hydroponics where the nutrient solution is in a single reservoir and only needs to be checked once, a soil garden will get its nutrients from the soil it is growing in. Even a small garden that contains a few plants may have soil that varies in pH from one area to another.
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 will stunt the plant and cause browning out of the foliage.
Also, as the plant gets older its roots become less effective in bringing food to the leaves. To avoid the accumulation of these salts in your soil and to ensure that your plant is getting all of the food it needs, you can begin leaf feeding your plant at the age of about 1.5 months.
Dissolve the fertilizer in water (worm castings mixed with water will work well for leaf feeding) and spray the mixture directly onto the foliage. The leaves absorb the fertilizer into their veins. If you want to continue to put fertilizer into the soil as well as leaf feeding, be sure not to overdose your plants.
Adjusting pH Of Marijuana Grown In Soil
A good way to stabilize soil is to use dolomite lime (calcium-magnesium carbonate). Dolomitic lime acts slowly and continuously, so soil will remain pH stable for a few months.
Using fine size dolomite lime is important, coarser grades can take a year or longer to work. You can find fine size dolomite lime at any well stocked garden supply center.
Dolomite lime has been used by gardeners as a pH stabilizer for many years. It has a pH that is neutral (7.0). When added to soil in the correct proportions, it will stabilize soil at a pH near 7.0.
When growing in containers, add one cup of fine dolomite lime to each cubic foot of soil. Mix the dry soil thoroughly with the dolomite lime, then lightly water it. After watering, re-mix it and wait for a day or two before checking the pH. When growing in an outdoor garden, follow the dolomite lime manufacturers instructions.
Lowering soil pH: small amounts of composted leaves, cottonseed meal, or peat moss will lower the pH of soil.
Raising soil pH: small amounts of hardwood ashes or crushed oyster/egg shells will help to raise the soil pH. Hydrated lime can also be used to raise the pH of soil. In containers, use no more than 1/8 cup of hydrated lime per cubic foot of soil (per application). Mix it into warm water, then apply the water to the soil. When growing in an outdoor garden, follow the manufacturers instructions.
Wait at least a day or two before checking the pH level of soil after attempting to raise, lower or stabilize it. If adjustments still have to be made, use small amounts of whatever material you are using. Don't try to adjust the pH more than 0.1 every two days.
