What’s the Best pH for Growing Medical Marijuana?

Scientifically speaking, pH represents the “potential Hydrogen” present in a solution. Which sounds smart, but what does it have to do with plants? Hydrogen is a core element that plants need to survive, without it the plant would not be able to absorb any nutrients found in the soil or fertilizers introduced. The hydrogen-osmosis allows the plants to continuously absorb nutrients traveling from the water to the plant’s root system.

While the scientific breakdown of pH may be of interest to some, the most important thing you’ll want to remember when you start growing is that pH measures the acidity or alkalinity of your water, growing medium, or nutrient solution. pH is measured on a sale from 1-14, with 1 being highly acidic, 14 being highly alkaline, and 7 considered neutral. A seriously important thing to remember when using a pH meter is a pH difference of 1.0 is equal to ten times an increase or decrease in pH. Therefore, a solution or substance with a pH of 5.0 is ten times as acidic as something with a pH of 6.0. In conjunction, a pH difference of 2.0 is equal to a hundred times increase or decrease in pH. In other words, be careful when adjusting. Baby-steps are your friend.

If you are growing hydroponically with inert growing media the pH of the nutrient solution should measure between 5.5 and 6.8, however many growers believe the optimal pH has a smaller margin, between 5.8 and 6.3.  There is no shortage of opinions when it comes to perfect pH for hydroponic growth. Some growers will argue for an even lower pH in the range of 5.2-5.9, while long-time growers may swear by a neutral pH of 7.0. A good rule of thumb to remember is to remain within a standard pH range and then adjust your individual plants from there depending on how they respond.

To adjust the pH of your hydroponic solution you will need to purchase pH-up or pH down solutions. These readily available products can be purchased at your local nursery, hydroponic store, or garden shop. There are also a variety of home-remedies that can aid you in raising or lowering pH levels. You can check out these methods and more here.

[twocol_one]To Lower pH:

  • Lemon juice
  • Phosphoric acid
  • Nitric acid
  • Hydrochloric acid

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To Raise pH:

  • Hydrated lime
  • Baking soda
  • Calcium carbonate
  • Potassium silicate

It’s not advised to try and adjust your pH more than 0.2 a day. Gradually increasing or decreasing is the best way to not overdose your plants. Unless the directions instruct differently, make large pH changes over several days. Check the pH of your nutrient solution at least once or twice a week after you mix your solution into the reservoir. You’ll also want to pay special attention to the quality of the water you use on your plants. It’s best to use dechlorinated, room temperature water. Letting your tap water stand for at least 24 hours will achieve both of these things and lower the risk of shocking your plants.

If you are growing medical marijuana in soil or soilless media, the “best” (again, lots of opinions out there and you will run into your fair share during your research) pH is between 6.5 and 7.0. If you are growing in multiple containers it is advised to have a single pH reading for each. If you are growing in an outdoor in-ground garden, take two or three pH measurements from different areas and depths of the garden. This will let you know if you need to adjust different areas of your garden accordingly. An excellent way to stabilize your native soil is by using dolomite lime because it is slow and continuously acting, allowing your soil to remain stable for months at a time. Add about one cup fine dolomite lime to each cubic foot of soil, then lightly water. Wait one to two days before remixing soil and checking the pH. If you are using a pre-mixed soilless blend, you’ll want to make sure lime has not already been added.

[twocol_one] To Raise pH:

  • Hardwood ashes
  • Oyster shell
  • Hydrated lime

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To Lower pH:

  • Composted leaves
  • Peat moss
  • Organic mulches

As with hydroponic pH adjustment, you should avoid attempting to lower or raise pH in large quantities. When growing in soil or soilless mediums and you have to make adjustments, use smaller amounts of whatever materials you have already introduced to the soil.

There are a variety of different ways to check the pH of your nutrient solution or growing media. Some of your options include:

  • pH Meter: used to measure the pH of water, hydroponic nutrient solution, hydroponic media, and soil.
  •  pH Test Kit: used to measure the pH of liquids like water or hydroponic nutrient solution.
  • Soil pH Meter: used to measure the pH of soil
  • 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.

For an in-depth explanation of each meter and where to buy them, check out this awesome article from the Growery.

The most important thing to remember is that the pH level of your nutrient solution or growing media will play a large role in determining how well your plants are able to absorb nutrients. Keeping the pH level in the proper range will ensure a steady growth rate and happy, healthy plants. Basically just be patient with your plants, stay within a stable pH range, and give ‘em lots of love and you’ll be rewarded with abundance.

For more info, check out some tips from a few growers in this forum. Just remember, lots of opinions out there regarding pH, but you got to do what’s best for your grow and your plants.