The ideal pH for coco coir cannabis grows is between 5.8 and 6.0 in the vegetation stage and 6.0 to 6.2 for flowering stage. The max range you’d want would be 5.5 to 6.5, growing pot in coco outside of that pH range will cause nutrient problems.
Your goal is to keep the coco coir medium at a pH of 5.8-6.0 or so which is ideal for proper nitrogen absorption by marijuana plants in veg. Varying the pH a bit in veg from 5.7 to 6.0 allows for nutrients that are best absorbed at slightly higher or lower levels. You want to go a bit higher for flowering to allow for better absorption of phosphorus and potassium.
You should always water your coco coir to runoff, aim for 10-20% to drain out the bottom of your container. This ensures the roots get fully saturated and the runoff removes excess nutrient salts that could lead to nutrient burn.
Measuring the pH of the runoff water
Measuring the pH of the runoff water helps you understand the pH of your coco medium and your cannabis plants’ root zone. If your runoff pH is too low or too high, you can adjust your next watering to bring it back closer to the proper range.
For example, if you’re seeing a 6.6 in your runoff during flowering, try 5.8 the next time to bring it down a bit, again measuring the runoff. Aim to get it down to 6.2 or so. Don’t go nuts.
If your pH range in coco coir is way off, flush a bunch of properly pH’d nutrient solution through your plant to get things back in line.
Keep in mind that separate plants need to be monitored independently, especially if running different strains. You should also be using a ppm meter to measure total dissolved solids while you’re measuring the pH.
How to fix pH problems in weed plants grown in coco coir
Thankfully it’s pretty easy to fix pH problems in weed plants growing in coco coir. Especially if you catch them early. For the most accurate results, test the pH of the coco’s runoff water to see how things are going inside the root ball.
Too high or too low pH levels will prevent the marijuana roots from being able to absorb necessary nutrients, something known as nutrient lockout. Weed plants suffering from nutrient lockout will show signs of damage, so monitor your plants daily and look for unusual symptoms.
How to lower the pH of coco coir
If your runoff pH is too high or too low, you can fix pH issues easily by flushing the coco coir with properly pH’d water.
For example. if your runoff shows a high pH of over 6.2, try running the next few waterings around 5.6 to 5.7 with about 25-30% runoff and you can bring this down easily. For a pH over 6.5, you’re entering the danger zone and you should flush several gallons per pot plant at 5.6 to make sure to correct the issue more quickly.
How to raise the pH of coco coir
If the pH of your runoff water is too low, say 5.6 or below, you can raise the pH of coco coir in a similar manner by flushing. Flush with water pH’d around 6.3 or so for severe problems and around 6.1 for minor corrections.
Once the runoff pH is back above the 5.7 mark you’re in good shape. Keep an eye on the runoff going forward to try and keep it around 5.8.
How to test pH in coco coir
A decent pH meter is well worth the investment to test pH in coco coir nutrient solution. Incorrect pH levels are the biggest cause of pot plant health problems among new weed growers. You’ll need to maintain an accurate pH every time you water. Don’t guess at it. Get a decent pH meter, adjust using a small amount of pH up or down, stir gently, and test again until you get it in the zone.
Wiggle your pH meter around in the water gently to get the reading to calibrate quicker. Watch for older meters with readings that slowly keep climbing, if this happens it’s time to recalibrate and it may be a sign you’ve fried the bulb and it needs to be replaced.
How to store a pH meter
Make sure to properly store it by adding pH meter storage solution (or clean water) to the cap and replacing it over the pH bulb after each use. Never let the bulb of your pH meter dry out, it will stop working correctly and you’ll need to replace it.
In our experience this can happen a lot if you’re not careful − especially if you’re smoking a jay while you work and you get distracted. Try to have good habits to avoid this, and make sure you replace the cap right away when you’re done using it..
Recalibrate your pH meter frequently
Every 3 months you should recalibrate your pH meter according to the instructions it came with to ensure accurate readings.
If you don’t recalibrate your pH meter you will end up giving improperly pH’d water to your weed plants and you’ll end up with nutrient deficiencies. If you identify a deficiency and the readings of your runoff water seem like they should be ok, you may have a recalibration issue.
Summary: The best pH for coco coir
The ideal pH for coco coir cannabis nutrient solutions is between 5.8 and 6.0 in vegetation and 6.0 to 6.2 in flowering. Try to keep the coco coir medium at a pH of 5.8-6.2. Alternate the pH of waterings to give a range.
Water to runoff of 10-20%, and monitor the pH of this runoff to catch issues early. For small issues just adjust your next watering. Correct bigger issues with too high or too low pH levels in coco coir by flushing your marijuana plants with properly pH’d nutrient solution.