matto70799
Member
First let me introduce myself. I am new to this forum and fairly new to marijuana cultivation, however, I understand pH, what it means (what are you actually measuring?), why it's critical to plant health, and the many methods for pH monitoring. Qualifications: I have a masters degree in molecular biology, several years of college botany and plant physiology, and I work in biotech for the past 10 years. Ok now that we have established I probably know what Im talking about....First, what is pH and why doea it matter to plant health. pH is literally the measurement of the proton (hydrogen ions with 1 proton, 0 neutrons, and 0 electrons, therefore they carry a +1 charge) content of a solution. Now this matters because the amount of hydrogen ions defines how basic (alkaline) or acidic a solution is and in the case of plants this matters because the nutrients in the soil can only be taken up by the roots within a certain pH range. So even though you bought the high end nutrients, water your plants, love them, encourage them, etc., if the pH is too high or too low they won't be able to use those expensive nutrients and you'll start to see signs of nutrient deficiencies. Marijuana grown in soil likes a pH range similar to that of tomatoes: ~6.0 to 7.5, grown hydroponically (without soil - only water to deliver the nutrients) the correct pH range is slightly more acidic: ~5.5 to 6.5. At these pH ranges the plants can readily dissociate the nutrient ions from the salt form in which they are often supplied (a salt in chemistry is the ionic product of a neutralization reaction of acids and bases. They are composed of a related amount of cations (positively charged ions) and anions (negatively charged ions) such that the resulting compound is electrically neutral (has a net charge of 0). For example: table salt is the salt of chlorine (Cl, anion) and sodium (Na, cation). Chlorine carries a -1 charge and sodium carries a +1 charge. When they come together to make a salt there is 1 of each atom resulting in the neutrally charged salt molecule (NaCl). Nutrients are supplied in their salt form. At the appropriate pH the salt dissociates (aka: dissolves) in water (so in our NaCl example when salt is dissolved in water what really happens is the ionic bond between the Na and the Cl atom breaks. So a solution of table salt contains free Na+ and Cl- atoms). The plant can then (usually through processes involving bacterial colonies in their roots) uptake the nutrients in a form it can use. Ok, so now, how do we measure pH? There are many ways depending on how accurate a reading you need, and your preference between matching up colors or just having a digital number displayed (also how much you want to invest). I personally use a Hach brand portable meter (about $400 retail). I understand I'm nuts, so I wouldn't expect most people to go out and get one of these sophisticated meters. Less expensive options for digital meters are called pH pens. (I put a pic at the bottom). There are many brands but i would try to stay with Hach, Oakton, VWR, or Mettler toledo. They are excellent quality manufacturers. These will cost about $50-$100 and all digital pH meters will require you purchase reference standards to calibrate. You'll want at least a 2 point calibration, and please, if you are most interested in the range of pH from 5-8 then by all means calibrate your meters with pH 4 and pH 10 standards. You want to bracket the pH range you will be testing with your calibration standards. I've seen websites recommend calibrating with pH 4 and pH 7 standards. This is great if your most interested in a range between pH 4 and 7. Anyway, less expensive and still good options include colormetric (a color change reaction) based tests: pH test strips (dip and match color result to chart), or liquid based tests (like for an aquarium). These last two options have the added pros of being cheap, no calibration needed, and they are quick. However you will sacrifice accuracy for price, which may or may not matter to you. Well i hope this quick little blurb helps someone out there. Ask any questions, happy to answer.
Last edited:
Jotting Notes
