The Perfect pH Value For Cannabis
In chemistry, pH is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. Solutions with a pH measured lower than 7 are acidic and solutions with a pH measured higher than 7 are basic. Pure water is neutral, at pH = 7 (only at 25 °C), being neither an acid nor a base.
Contrary to popular belief, the pH value can be even lower than 0 or even higher than 14 for very strong acids and bases respectively. The pH of aqueous solutions can be calculated using a pH meter, pH papers, pH drops. While a pH meter is used for accurate calculations, pH papers, and pH drops are used for more general results.
In many cases, various nutrient deficiencies or toxicities that may occur in your plants are directly connected to either too high or too low pH levels, whether in growing medium or the water used for watering your plants.
So, instead of increasing or decreasing certain nutrients and trace elements in your nutrient solution, it’s important to know and maintain the proper pH levels needed for your cannabis plants to grow optimally.
How does pH stop Cannabis nutrient deficiencies?
A cannabis plant naturally grows best in a slightly acidic environment at its roots. It prefers a pH environment valuing from 5.5 to 7, depending on the medium you use. When the pH environment rises in basicity above 7.5, the roots are not able to consume the available Iron, Copper, Zinc, Manganese, and Boron Ions in their vicinity, and when the pH lowers into acidity below 5.5 the roots are not able to access Phosphoric Acid, Calcium, and Magnesium because they lose their solubility. If the pH drops its value between 5 to 3 with temperatures above 26 °C fungal diseases become a threat to the plant.
By maintaining the proper pH levels, cannabis plants will suffer less from leaf problems and nutrient deficiencies, and will be able to grow faster, producing bigger yields, as there will be no nutrient problems.
Optimal pH Value For Different Used Mediums
Soil
The optimal pH value for soil is between 6 to 7, with the most common values being between 6.2 and 6.9. It is preferable to let the pH cover a wider range instead of always adjusting it to the exact same value.
In soil based mediums that don’t use liquid nutrients, such as ‘living soil’, pH is not a crucial factor. However, when liquid nutrients are used, there will be a greater need for managing the pH in order to prevent problems and get the most of a plant.
Soilless, Hydroponics & Coco
The optimal pH value for soilless, hydroponics or aeroponics, and coco is ranged from 5.5 to 6.5. It is especially important to allow the pH to range slightly, as some nutrients can only be absorbed at higher or lower pH values.
In a soilless type of medium, there will always be a need for using liquid or powder nutrients. So in order for things to be easier, pH should be watched and adjusted as needed. The pH will naturally change over time and will only need correction when its value starts getting out of the 5.5 – 6.5 range.
pH Symptoms
Low pH (Acidity)
When the pH becomes more acidic than preferable, certain symptoms will appear which are most commonly connected with deficiencies of Phosphoric Acid, Calcium, and Magnesium.
In Phosphoric acid deficiencies, fan leaves may turn from dark green or red / purple, into yellow. Leaves may curl downwards, and even turn brown and die. Having small and thin buds is another main symptom. Phosphoric acid deficiencies exhibit slow growing, weak and stunted plants with dark green or purple pigmentation in older leaves and stems. Some Phosphorus deficiencies during the flowering stage are normal, however too much shouldn’t be tolerated. Red petioles and stems are normal, genetic characteristics for many strains but it can also be a co – symptom of Nitrogen, Potassium, and Magnesium deficiencies, so red stems are not a certain sign of Phosphorus deficiencies. On the other hand, too much Phosphorus can also lead to Iron deficiencies.
In Phosphoric acid toxicities, excess phosphorus can interfere with the availability and stability of Copper and Zinc. Luckily, this condition is rare and usually buffered by pH limitations. In Calcium toxicities, excess Calcium may produce deficiencies in Magnesium and Potassium.
In Magnesium deficiencies, the older leaves are the ones which will get affected first, exhibiting a yellowing (which may later turn brown) and inter – veinal chlorosis that will start at leaf margin and tips, and progress inwards between the veins.
In Magnesium toxicities, excess Magnesium, at extreme high levels, will antagonize other elements like Calcium, Chlorine, and Ammoniacal Nitrogen. Fortunately, these toxicities are rare, however not generally exhibited visibly.
High pH (Basicity)
When the pH becomes more basic than preferable, certain symptoms will appear which are connected with the deficiencies of Iron, Copper, Zinc, Manganese, and Boron Ions.
In Iron deficiencies, the effects are similar to that caused by Magnesium deficiencies, with the only difference – the affected leaves are the younger ones, starting from the lower and middle parts of the plant.
In Iron toxicities, excess Iron accumulation is rare, but could cause bronzing or tiny brown spots on the leaf surface. Manganese is involved in the oxidation – reduction process in the photosynthetic electron transport system. Biochemical research shows that this element plays a structural role in the chloroplast membrane system, and also activates numerous enzymes.
In Copper deficiencies, the symptoms are a reduced or stunted growth with the young leaves often becoming dark green, twisted and / or distorted. The leaves may die or just exhibit necrotic spots. The growth and yield will be deficient as well.
In Copper toxicities, excess values of Copper will often induce Iron deficiency. Root growth will be suppressed followed by symptoms of Iron chlorosis, stunting, reduced branching, abnormal darkening and thickening of roots.
In Zinc deficiencies, the deficiencies appear as chlorosis in the interveinal areas of new leaves producing a banding appearance. This may be accompanying the reduction of leaf size and shortening between internodes. Leaf margins are often distorted or wrinkled. Branch terminals of flowers will die back in severe cases.
In Zinc toxicities, excess Zinc interferes with Iron causing chlorosis (especially to sensitive plants) from Iron deficiencies. Excess Zinc is extremely toxic and will cause rapid death.
In Manganese deficiencies, Interveinal chlorosis of young leaves, necrotic lesions, and leaf shredding are some of the typical symptoms of these deficiencies.
In Manganese toxicities, high levels Manganese can cause uneven distribution of chlorophyll resulting in a blotchy appearance. Restricted growth, decreased vigor, and failure to mature normally are often some of the most common symptoms and signs that Manganese levels are too high.
In Boron Ion deficiencies, plants exhibit brittle abnormal growth at sprout tips and one of the earliest symptoms is failure of root tips to elongate normally. Stem and root apical meristems often die. Root tips often become swollen and discolored. Internal tissues may rot and become hosts to fungal diseases. Leaves show various symptoms which include drying, thickening, distorting, wilting, and chlorotic or necrotic spotting.
In Boron Ion toxicities, toxicities cause yellowing of leaf tip followed by necrosis of the leaves beginning at the tips or margins and progressing inward before the leaves die and prematurely fall off. Some plants are especially sensitive to boron accumulation.
Testing & Adjusting The Medium’s pH
Testing Equipment
The most common, accurate, and easier way of testing the medium’s pH is using a pH meter. Other methods include pH papers, and pH drops, though they tend to be less accurate than pH meters but could help you identify a potential issue.
pH Adjustment
The pH can be adjusted using special solutions called pH buffer solutions. These solutions are either acidic or basic in order to adjust a basic environment or acidic environment, respectively.
Another way of adjusting the pH is using nutrients or water supplements. The reason is that every time nutrients are used, they will always change the medium’s pH.
Tips & Common Problems
There are a few tried and true rules for making sure the calculations are accurate.
The right pH buffers must be used. pH meters work best when calibrated slightly above and below the wanted range of testing.
There must be an understanding of what can quickly adjust the chemical composition acidity and basicity. For example, adding garden lime can make water and soil more basic. White vinegar can make both water and soil more acidic.
The plants must be flushed with corrected water if they are out of pH range. This will also help correct the pH of the soil itself.
Sanitary conditions when testing are critical. Always use fresh buffer test liquid. The meter must also be clean. Contamination of either will affect the readings.
Proper storage is essential. All pH meters contain a pH electrode, which is very sensitive. If it is damaged or dried out, it will not give an accurate reading.
There mustn’t be used distilled or deionized water at any point of the process. This can damage the sensing glass of the pH meter.
Common Problems & Answers
When using pH drops, you often can’t notice what color the water is changing into.
The addition of more drops of indicator fluid will help, as well as using fewer drops. When there is not enough or too much of the indicator fluid in the vial, it makes it really hard to tell what color the water is turning into.
The pH meter is not working
Firstly, the meter must be checked for damages. Is the electrode broken? It looks like a glass bulb on the end of the steel bar. Next, was it stored properly? What that means is, was the glass bulb stored with storage fluid in the cap. If it was stored dry, the bulb can break even if everything looks fine. If the meter was stored under the perfect conditions then it must be about the correct calibration. Was the meter recently calibrated with the 4 and 7 values calibration fluid? An uncalibrated pH meter can give wildly inaccurate readings. Lastly, at what condition the battery exists? These batteries last a really long time but it is still a good idea to check and replace them regularly.
The pH keeps changing while it is being tested.
Something to keep in mind is shaking the water actually temporarily raises the pH. So if the water is shaken and tested again, it will be noticed that the pH reading is different each time. If pH drops or papers are used, make sure the directions are closely followed. Adding too much or too little drops will make it impossible to accurately track the pH. If a pH meter is used, make sure the pH tester is working – by testing it on 4 and 7 pH values calibration fluid.
The runoff pH is too high / low, how can this be fixed?
If the pH is really off the preferable pH range, or if the plant is suffering from toxicity or severe nutrient burn, it may be a good idea to flush the growing medium first. What that means is that the plant is given enough water to get lots of runoff. This helps “flush” out any extra nutrients or salt buildup in the soil.
Only flush if it is absolutely needed, though. Flushing can temporarily slow down the growth of the plant, and you should give your plants plenty of time to dry out and for fresh oxygen to get to your roots. If the runoff is only off by a slight, the pH will be corrected by changing the amount of the pH buffer solutions, which are provided to the plant, when watering.
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