Coco coir pH chart: What is the best pH for growing weed in coco coir?

The best pH for coco coir weed plants is between 5.8 and 6.0 in the vegetation stage. The best coco pH for flowering is between 6.0 to 6.2. The max coco coir pH range you’d want would be 5.5 to 6.5. Growing weed in coco outside of that pH range will cause nutrient problems.

Your goal is to keep your nutrient solution at a pH of 5.8 to 6.0 which is ideal for proper nitrogen absorption by marijuana plants in vegetation. Varying the pH a bit in veg from 5.7 to 6.0 allows for other nutrients that are best absorbed at slightly higher or lower pH levels.

You want to go a bit higher with your coco pH range during flowering to allow for better absorption of phosphorus and potassium.

A good pH pen is essential. It’s one of the most important tools to ensure a successful grow. The BlueLab pH pen ($80-90) is your best choice. Budget-minded growers can choose the more affordable Hanna pH pen ($30).

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.

Never let your containers sit in this runoff, use a plastic plant stand to elevate your pots above the runoff to avoid issues. A shop vac can remove water that accumulates.

Measuring the pH of the runoff water

If you suspect you’re having deficiencies caused by pH issues in coco coir, you can try measuring runoff pH to see where you fall on the coco pH chart.

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.

If you find your pH in coco coir is way off, flush a bunch of properly pH’d nutrient solution through your plant to get things back in line. Aim for lots of runoff.

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 runoff coco pH.

Don’t go nuts spending all your time chasing runoff pH. It’s a tool available if you suspect pH problems with your weed plants. But spending hours tracking runoff if your plants seem otherwise healthy isn’t the best use of your time unless you’re really seeing issues.

Help! I’ve really fucked up my coco coir pH!

If you’ve really fucked things up with the pH in your substrate and your coco ph is off the chart then you may need to take more decisive action. Slowly flush with 2x to 3x your container size of plain pH’d water to really flush it out. Then an hour later run some more through.

It’s better to do this slowly to ensure that all the of the coco in your container is properly addressed. If you go too fast the flush water may just pour through areas of the root ball with the lowest density; reducing effectiveness of the flush.

At this point your coco will be saturated with water that is devoid of nutrients. So you’ll need to mix up your nutrient mix and rewater to ensure your plants don’t go hungry.

The coco coir pH chart shows the scale used to gauge the acidity of liquid nutrient solutions for marijuana. 7 is neutral; the lower the number the more acidic it is; the higher the number the more alkaline.
This coco pH chart shows the pH scale used to gauge the acidity of liquid nutrient solutions for marijuana. 7 is neutral; the lower the number the more acidic it is; the higher the number the more alkaline.

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.

Using pH down is needed to lower the pH of your nutrient water to the ideal range of 5.7-6.0. To correct pH problems in coco coir, flush with lots of properly pH'd water.
Using pH down is needed to lower the pH of your nutrient water to the ideal range of 5.7-6.0. To correct problems with the proper pH for growing weed in coco coir, flush with lots of properly pH’d water.

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. Use pH Down or a similar product to adjust the level.

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.

Use pH can raise the pH of your nutrient solution to bring it into the ideal range. You won't use all that much pH up compared to pH down though, since your water is likely starting near 7.0.
pH up can raise the pH of your nutrient solution. Since your water is likely starting near 7.0. you’ll use a lot more pH down on a regular basis. pH up is often used to correct overaggressive applications of pH down.

How to raise coco coir pH

If the pH of your runoff water is too low, say 5.6 or below, you can raise your coco coir pH 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.  Your goal is to flush slowly, so apply the water in small amounts at first to let it absorb into your coco medium, and then continue to add water slowly so it drips out of the bottom.

pH up or similar products can help you adjust your water to the proper pH.

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 good pH meter is well worth the investment to test pH in coco coir nutrient solution.  Consider the BlueLab pH pen ($80-90) which is the best choice. It’s very accurate and fully waterproof.

For budget-minded growers, the Hanna pH pen (under $30) is a good option.  I’ve used several of these before switching to Bluelab’s pen. Hanna also makes a better-quality waterproof pH pen ($78) that works well.

Incorrect coco coir pH levels are the biggest cause of cannabi plant health problems among new weed growers. One of the important growing in coco tips is 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 using a dropper, stir gently, and test again until you get it in the zone.  Eventually you’ll start to learn about how much you’ll need each time.

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. It’s impossible to maintain your plants in the proper range on the coco ph chart if your meter is giving incorrect readings.

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

Most pH meters come with a few envelopes containing calibration solution for the first time you do it.  You can pick up pH meter calibration solution on Amazon for under $10.

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.

I’ve heard from several growers who were running into-head scratching pH issues that were resolved through a simple calibration.

Summary: The best pH for coco coir

The best coco coir pH for 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 within the range of the coco pH chart.

Water to runoff of 10-20%, and monitor the pH of this runoff to address 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.