What the best pH value for cannabis plants ?

WHAT IS PH?
pH is a measure of how acidic or alkaline something is. The pH scale ranges from 1-14, with a pH of 7 being neutral (the pH of pure water). If pH is lower than 7, a substance is considered acidic (think vinegar or lemon juice). If the pH is higher than 7, the substance is alkaline, as is the case with soaps, bleach, and ammonia.

In more scientific terms, pH level has to do with the concentration of hydrogen ions, say in the water you give to your plants. The pH scale is logarithmic to the base 10, which means that water with a pH of 6 is already 10x more acidic than water with a pH of 7.






Why is pH Important in Growing marijuana?

The pH in the growing medium of any plant has a massive effect on the availability of the nutrients in the medium at the plant's roots. Marijuana thrives best in a slightly acidic growing medium. The reason for this is to do with the natural environments where marijuana first evolved. In fact, with a few exceptions, most plants prefer a slightly acidic pH.

The ideal pH for growing marijuana should be considered as a range rather than a specific number. This is because different nutrients become available to the plant at slightly different pH levels. By having your pH sitting within a range rather than at a specific point, you make more nutrients available.

Take a look at the diagram above. The pH range is marked along the bottom. Just follow the lines up to see the uptake and availability of different nutrients at different pH values. Note that in soil there are much smoother lines. This shows how soils act as a buffer. Compare this with the lines of the hydro chart and you can see that there is more room for manoeuvre when growing in soils as opposed to hydroponics. If you are growing with properly amended or composted soils then there is a much lower chance of running into pH problems.

From the diagram we can see that:
The optimum pH for marijuana in soil is around 6.0 - 6.8
The optimum pH for marijuana in soilless or hydro is around 5.5 - 6.5

If you grow in a soilless medium like coco, but with added organic matter (worm castings for example), you should consider aiming for a pH value somewhere between soil and hydro. Remember though, you are looking for a pH range rather than an actual number.

If the pH of your growing medium veers outside of these ranges, certain nutrients and trace elements will no longer be available to the plant. This means that the plant may begin to show symptoms of deficiency in a particular nutrient, even though that nutrient may be physically present at the plant's roots.

If you are unable to monitor and understand the pH of your growing medium you can end up in the position (and it happens A LOT) where you are feeding a plant more and more nutrients to fix a deficiency and the plant simply cannot take them on board. If unchecked this situation can lead to a build up of salts in the growing medium which block up the plant's roots. This is nutrient lock out. Your plants can literally die of starvation despite how much you are feeding them.
WHAT IS THE CORRECT pH FOR CANNABIS?

A natural assumption is that sitting pretty with a pH of 7 would be ideal-many of us often see the middle ground as a safe space. Instead, cannabis plants prefer more acidic media. A slightly acidic growing medium also supports beneficial fungi.

An important side note at this point; even moving one number up or down on the scale will have a significant impact on your cannabis plants. A substance measuring a pH of 6 is ten times more acidic than a pH of 7. A pH of 5 is a hundred times higher in acidity. Smaller, menial adjustments are always the preferred method with pH, providing limited stress to your beloved weed!

To further complicate matters, depending on the grow setup you have opted for, the required pH also varies
pH in Hydro:5.5-6.5 pH




If you grow marijuana in a hydroponics system then pH management is a much more important issue. With no soil to act as a buffer changes in your pH values take effect much more quickly. With hydro grows allowing your pH to fluctuate within a prescribed range is important as it allows all of the nutrients in the solution to become available to the plant in turn. Luckily, this happens naturally as the pH of the solution in your hydroponic reservoir will drift over time.

When making up the nutrient solution for your hydro set up, always mix the separate components in the water. Never mix them together directly as this can cause them to chemically react with each other and may change their desired properties.

Mix your nutrients gently. Overly vigorous mixing adds oxygen to the solution and this will temporarily raise pH levels. Some growers like to shake their solution vigorously to add oxygen which is good for the roots. If you like to do this, do it after you have checked and adjusted the pH.

Make your mix in a clean reservoir and check the pH. Let the mix stand for an hour and check the pH again. The pH of nutrient solutions often changes quite quicklywithin the first hour so you should recheck and adjust as necessary.

If you are topping up your solution, or adjusting the pH in your reservoir, try not to subject the plants to drastic changes in pH which will stress them. Make changes slowly. Do not mix nutrients or pH regulators directly into the plants' reservoir. Make a mix in a separate container first then add that to your reservoir so that changes take place slowly.

Remember that pH drift is not only normal, it's desirable. Allow the pH in your reservoir to change gradually, but make sure you keep within the range of 5.5 to 6.5.
pH in SOIL: 6.0-7.0 pH






If you grow in soil, the optimal pH level for the root zone is between 6.0 and 7.0. However, there is no set number within this range that is "best". Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake. So as you adjust, try a slightly different reading each time. You can, for example, adjust your pH to 6.2 for one watering, then 6.6 the next. As long as it stays within 6.0-7.0, you should be fine. Soil is also more forgiving when it comes to pH imbalances, but it can only give so much.

If you grow purely organically-where you do not administer liquid nutrients-pH is less of an issue. If you're using amended and composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots. However, most growers using standard potting mixes and liquid nutrients will indeed have to reckon with pH.
HOW TO TEST PH

Managing pH level means testing the water or nutrient solution and adjusting it accordingly. This may sound complicated, but it really isn't.

To test pH, you can use a digital pH meter, or a pH measurement kit with drops. Opinions here differ as to which method is "best". Some prefer digital pH meters because they are accurate and easy to read, while others like the drops as they are super simple and don't require calibration. Try them both and see which you prefer.

Measure the pH after you add any nutrients or amendments as they will change the pH value of your water. After you mix the solution, use the pH meter or drops to test the pH level. If you are growing hydroponically, test a sample from your water reservoir a few minutes after you add your nutrients.
How to ADJUST pH

Again, when the pH drifts into unwanted territory, adjustments must be made. Below are standard corrective procedures used to modify substrate pH for plants grown in soilless substrates in greenhouses and adapted for cannabis.

1. Low Substrate pH Correction When Fe toxicity and Mn toxicity become a problem, raise substrate pH to the recommended pH range. Corrective procedures to raise low pH levels are listed on p. 52 (Table 1). Switching to an alkaline fertilizer when substrate pH is nearing the lower limit will help stabilize the pH.

Flowable Lime

To make small adjustments of roughly 0.5 pH units, mix 1 to 2 quarts of flowable lime per 100 gallons of water. If using an injector, avoid using higher concentrations of flowable lime as it will damage it. If higher rates are needed, then split your applications to avoid damaging your injector. To avoid leaf burn, it is best to rinse the foliage after treatment if any flowable lime comes in contact with the leaves.

Hydrated Lime

For more stubborn low-pH problems, use a hydrated lime mixture. Mix 1 pound of hydrated lime in 3 to 5 gallons of warm water. Mix it twice and let it settle after each mixing. Once the sediment collects in the bottom of the container, pour the liquid through your injector system set at a 1:15 ratio. This product is corrosive, so rinse the foliage as soon as possible to avoid leaf burn, and avoid skin contact.

Potassium Bicarbonate (KHCO3)

Potassium bicarbonate should be handled with care. It can throw off your substrate chemistry as it provides 993 ppm of potassium (K) in mixtures of 2 pounds per 100 gallons of water. Rinse the foliage immediately after application via injectors and leach heavily the following day with a complete fertilizer to reduce substrate electrical conductivity (EC) and restore nutrient balance. The 2-pounds rate will increase the substrate pH by roughly 0.8 pH units. Rates greater than 2 pounds per 100 gallons of water can cause phytotoxicity.

As always, remember to recheck your substrate pH to determine if reapplications are needed.

2. High Substrate pH Correction The target pH for cannabis is between 5.8 and 6.2. Higher pH values may result in Fe deficiency and create interveinal chlorosis on upper leaves. Check the substrate pH to determine if it is too high. Be careful when lowering the substrate pH, as low pH can be more problematic and difficult to manage.

Cannabis plant growth is less vigorous at low substrate pH levels.

Acid-Based Fertilizer

If the substrate pH is beginning to increase, consider switching to an acidic-based fertilizer. These ammoniacal nitrogen (N)-based fertilizers are naturally acidic, and plant nitrogen uptake will help moderate the substrate pH over a week or two.

Acid Water Drench

Some growers use this intermediate correction when pH levels are not excessively high and a quick lowering of substrate pH is desired. Sulfuric acid is recommended to acidify irrigation water to a pH 4.0 to 4.5. Apply this acid water as a substrate drench, providing 5 percent to 10 percent excessive leaching of the substrate. Rinse the foliage to avoid phytotoxicity. Results should be visible within five days. Retest the substrate pH and repeat if needed.

Iron Drench

If the levels are excessively high, then a Fe chelate application can be made to the substrate.
Iron-EDDHA can be mixed at a ratio of 5 ounces per 100 gallons of water.
Iron-DTPA can be mixed at a ratio of 5 ounces per 100 gallons of water.
Iron sulfate can be mixed at a ratio of 4 ounces to 8 ounces per 100 gallons of water.

Apply the iron as a substrate drench with enough volume to leach the pot, and rinse the foliage immediately after application.
WHEN SHOULD I TEST pH?

As much as possible is the simple answer. A balanced pH will give your cannabis plants the best chance of reaching their optimal potential.

Testing the pH of your grow every week-the pH of your nutrient solution before watering, the pH of your growing medium a couple of days after a feed, and the pH of the water after drainage-will all ensure the correct levels are maintained. A simple check could save your plants from disaster.
Conclusion

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