Correct PH for cannabis plants, Ph up, Ph down, marijuana, weed

pH Fluctuations

Ph Fluctuations Solved

Problem: Brown or tan spots appear on the leaves. 

If you water your plants with the wrong pH over several days, they will grow at a slower rate and suffer from nutrient deficiency, making pathogens and pests more likely to make their appearance. Under these conditions, the plants will also look weaker and duller, with discoloured leaves dry on the ends and yellowish, brownish spots scattered all over. These symptoms are easily detectable by daily visual inspection.

Note: This is more common in hydroponic systems where the pH is drifting dramatically, but of course it can also happen in soil.  Brown spots on the leaves can also mean other things so what we should do is learn to dial in the perfect pH for our cannabis strain and then we can eliminate pH fluctuations as the cause. 

What Is Happening?

Managing pH is crucial to allow cannabis plants to be able to allow nutrient uptake.  Typically at lower pH we see more P & K available. At higher pH we would see something like more calcium available.  So keeping your pH to high or too low effects the nutrient uptake of the cannabis plant.

Light Burn Cannabis LeafNote: keeping pH too low creates an acidic environment that invites things such as pythium disease.  Pythium is less prevalent when the growing medium’s pH is below 5.5.  Pythium is the most common problem that growers experience. Pythium consists of approximately 125 different species, not all of which are plant pathogens, and is found in almost every environment.

The Solution

By understanding pH drift you can set pH to an optimal range, typically 5.8-6.2.  If indeed Ph fluctuations are the issue, then all you have to do is dial this in and watch your problem go away.

Understanding pH Drift

Should pH be set and always stay at 6.0? The answer is NO!

The topic of pH levels are a hotly debated topic for cannabis growers.  So let me back up my reasoning from some knowledge from David Robinson, Author of the Grower’s Handbook.

David says “Plants secrete acids and bases in their root zone to adjust the pH depending on what nutrients they want to eat. If a plant wants more phosphorous and potassium, it may actually secrete an acid, dropping the pH of the rest, so that it can uptake more P and K. It is also possible if the plant wants more calcium, for instance, that it may raise the pH in order to make that calcium more available. If we decide that 6 is the perfect number and every single time the point moves to 6.2 or 5.8 and we run in there and adjust it, it is possible we can be working against our plants.”

So no!  The pH does not need to stay at one point all the time from start to finish. If we allow our plant to choose what it needs, we’re allowing the plant to optimize its root zone environment.

All The Right Gear – pH Meters

In Season 1 Episode 3 of Growing Exposed <WATCH Episode 3 here >

I ran into the guys from HM Digital at the LIFT Tradeshow in Vancouver, Canada.  HM Digital is a world recognized company for providing the best values in water testing instrumentation, especially pH meters for the hydroponic industry. 


What is a pH Meter?

A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH.  The difference in electrical potential relates to the acidity or pH of the solution.

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HM Digital and Blue Lab are considered the best/most popular pH meters for growing cannabis.

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pH Up And Down Products

Measuring the solution’s pH levels allows a grower to see if their nutrients/plants are either too acidic or not acidic enough (alkaline).

Upon determining that their nutrient solution’s pH is too low (too acidic), a grower can make quick adjustments by using pH Up products, which usually contain potassium hydroxide and potassium carbonate.

Add a little at a time if your nutrient solution’s pH is too low in order to raise the pH to the proper level. While store-bought solutions are recommended, growers can use regular baking soda as a pH Up solution.

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Because pH values rise quickly with minimal input, it is advisable to start off with very small amounts of pH Up and continue testing the solution with a pH pen, pH meter, or litmus paper until the ideal pH value is reached. In hydroponics.

Note: It is considered easier to raise pH levels than it is to lower them.

Many things can affect the garden’s pH values, including nutrient levels, water quality, algae growth, and the choice of grow medium. Also, pH values change over time as plants grow and uptake more and more nutrients.

Managing pH

Learn how to manage your pH in this video by The Garden Sage. 

Adjusting the ph is an important concern for growers and gardeners. Adjusting pH allows us to have the optimum range for the nutrient uptake we want for our plants.

There’s a couple of ways to adjust pH. You can use home remedies like baking soda, sodium bicarbonate, and vinegar, or use a product designed specifically for this purpose, which are usually better than any home remedy. Things like sodium bicarbonate could cause you to end up with excess levels of sodium in your nutrient solution, so typically growers are using phosphoric acid and potassium hydroxide. These are decent pH adjusters, but can pH be adjusted organically? The answer is yes. For example, products like potassium bicarbonate and citric acid can be used to adjust pH.

I hope you have found the is article helpful to answer the question of what the proper pH for weed should be and how you can spot and fix a problem.

If you want to check out more about the series then check out our home page for new garden tours each month.

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