How to Spot Nutrient Deficiencies
PH is the measure of how “acidic” or “alkaline” something is, on a 1-14 scale. A pH of “7” is considered neutral, for example pure water has a pH of about 7. The measurements of pH has to do with the concentration of hydrogen in the sample. Growers can measure the pH of a water sample using special pH tester drops or a digital pH pen, like the one shown here on the right. Proper pH at the roots helps plants get access to the nutrients they need. If the pH at the roots is too high or low, the plant can’t properly absorb nutrients.
Paying Attention to pH Gives You Healthy Leaves
By maintaining pH…
- plants are less likely to suffer leaf problems or nutrient deficiencies
- without nutrient problems, cannabis plants can grow faster and produce bigger yields
- occasionally growers are alerted to possible issues before they become a problem, for example if you determine the pH is too high or too low, you can fix it before your leaves start suffering from deficiencies
The main thing to remember is that maintaining the right pH at the cannabis roots helps the plant absorb nutrients. Why is that?
Nutrients take different forms (on a chemical level) depending on the pH around them. Some forms are easier for the roots to absorb than others. When the pH is too high or too low, the plant can show signs of a nutrient deficiency even when the nutrients are physically there at the roots.
With pH, you’re helping plants get access to all the nutrients all the time. While pH is important for all grows, it is most important for growers using nutrients. The way that liquid nutrients are formulated, they are highly available to plant roots, but only in the right pH range.
What’s the Right pH?
- Soil – 6.0-7.0 pH
- Hydro/Soilless/Coco – 5.5-6.5 pH
As a result of the pH being too high or too low, cannabis plants may start showing signs of nutrient deficiencies even if the nutrients are available in the growing medium.
Once you get the hang of maintaining the pH, it’s a breeze and will take you only seconds. And after you have your grow dialed in, you may not even need to check pH as often because you know what to expect. The following charts show you how easy it is for the plant to absorb each nutrient at different pH levels. This can give you something to aim for when you notice a specific nutrient deficiency. In the wild, cannabis prefers a slightly acidic soil environment. For soil an optimum root zone pH for cannabis is between 6.0 and 7.0, with the most time spent with a pH between 6.2 – 6.9. It’s a good idea to let the pH cover a range instead of always adjusting to the exact same pH number.
See which nutrients are best absorbed at which pH levels
In a soil environment that doesn’t use liquid nutrients, pH isn’t as important. When using liquid nutrients in soil, you will almost always need to manage pH to prevent problems and get the best harvest. For hydroponic growing setups (as well as soilless growing mediums like coco coir) an optimum root zone pH is between 5.5 and 6.5. This is slightly more acidic than the optimal root pH for growing in soil.
It’s a good idea to let the pH cover a range instead of always adjusting to the exact same pH number.
See which nutrients are best absorbed at which pH levels
With hydroponics, it’s especially important to allow the pH to range slightly, as you can see above, some nutrients can only be absorbed at higher or lower pH’s.
In a hydroponic setup, you will almost always be using liquid or powder nutrients, so save yourself a ton of trouble by watching and adjusting the pH as needed! The pH will naturally change over time, and you only need to correct it when it starts going out of the 5.5-6.5 range.
What about soilless mediums like coco coir?
Most soilless growing mediums are completely inert, which means they don’t contribute any nutrients to the plant. Instead they act more as a support system for your roots while you provide all the nutrients through the water. When the plant is getting all it’s nutrients in the water, it’s considered a “hydroponic” growing setup.
However, some soilless growing mediums with a lot of organic matter may need a slightly higher pH to thrive. For example if you heavily amended your growing medium with worm castings (worm poop), you will want to aim for a pH between soil and hydroponic ranges since you’ve added “soil-like” components.
No Need to Be Exact – Let pH Range Up & Down
The thing to remember with pH is that you don’t need to be exact. What you do need to be is consistent in keeping the pH from creeping too high or too low in your plant root zone.
As long as you stick within the recommended pH ranges above, you will prevent the majority of all nutrient problems caused by too-high or too-low pH.
Why is it a good idea to let the pH cover a range instead of always adjusting to the exact same pH number? Some nutrients are better absorbed at slightly higher pH readings, while others are absorbed better at lower pH readings. Not having to try to pinpoint an exact number also saves a lot of unnecessary frustration.
If your marijuana plant roots are experiencing the wrong pH, it’s recommended you react as soon as you notice, and not wait until you actually notice problems with the leaves. It can be tempting to ignore a pH problem, but you’ll often get the best results by acting before your plant displays a problem. That being said, if your plant is growing green, vibrant and healthy, sometimes the old saying applies, “if it ain’t broke, don’t fix it.”
Be consistent in making sure pH stays in the range
You don’t need to be exact, just keep an eye on things and react if you notice the pH is getting too high or too low
Add all of your nutrients to your water first before checking and adjusting the pH. Your nutrients will affect the pH of your water so it’s important they get added before making any adjustments.
‣ PH Tester
Digital pH Pen or
pH Measurement Kit with drops or strips
These are the two most common methods for measuring water pH when growing cannabis. Learn more about the pros and cons between a Digital pH Pen or a pH Measurement Kit.
‣ PH Adjuster
A bottle of “PH Up” and a bottle of “PH Down”
A bottle of PH Up & PH Down gives you one of the best ways to adjust pH in soil or hydro. They each come in a bottle that lets you easily measure how much to add to your water. General Hydroponics makes the most common version of products like this, but there are other brands such as Mad Farmer which make similar products that are just as good.
There are other methods of adjusting pH, but using pH Up and pH Down is the best method I’ve tried – I know these products work great for growing cannabis, and they keep the pH more stable than natural alternatives like vinegar or baking soda.
For many growers, tap water works just fine for growing cannabis. Do you need special water?
I use a container that was originally made for drinking water to mix up my nutrients, but many different types of containers will work. Most importantly, avoid anything fragile, especially glass (which can break your instruments or shatter).
‣ Nutrients (If You’re Using Nutrients)
Learn more about cannabis nutrients – do you need them for your setup?
Add Any Nutrients or Supplements to Your Water – always do this first because nutrients can change the pH of your water
Gently Shake or Stir Your Water
Test pH – this is done using a pH Pen, drops, or strips. Which one works best?
Adjust pH by adding “PH Up” or “PH Down” solution. Your goal is to get your water in the right pH range for your growing medium. If your pH is too low, you need to add “PH Up,” and if your pH is too high, you need to add “PH Down” in order to correct the pH.
Re-test to make sure pH is in proper range.
Water plants with pH’ed nutrient solution or add water to hydroponic reservoir
Check – Soil or soilless growers who hand water their plants should check the pH or their runoff water to make sure it’s in the right range – try to test the earliest runoff if possible. Hydroponic growers can check the pH of their water by testing a small sample from their water reservoir a few minutes later. How do I correct a bad pH?
The amount of pH Up or Down you add will vary a lot depending on your water. If you’re using very soft water than you will need just a tiny amount of fluid to adjust the water’s pH since there’s not much “stuff” in the water to buffer the pH. However, if you’re using hard water than you’ll need to add more.
- For PH Down – 1 mL/gallon of water will generally reduce your pH about 1 point. That’s just a very rough estimate, but gives you a starting point. In imperial measurements, that’s 0.2 tsp/gallon (1 tsp/5 gallons) will reduce the pH by 1 point. If you’re regularly measuring PH Down I highly recommend using a blunt-tip syringe with mL measurements, it’s much simpler because imperial measurements don’t have precise enough measurements for the small amounts needed with PH Down!
Note: If you are starting with RO (reverse osmosis) or soft water, you likely need less PH Down than the specified amount; if you have very hard water you may need more!
- For PH UP – PH Up is not potent stuff! It actually has a very weak effect. Compared to PH Down you will need to add much more PH Up to adjust the pH by the same amount. With PH Up, depending on how hard your water is you need to add 2-4mL/gallon of water to raise the pH 1 point. In imperial measurements that’s 0.4-0.8tsp/gallon.
- The first time you’re adjusting, you don’t know what pH your water is, how “hard” it is, and how your particular nutrients and supplements are going to affect the pH. Initially, you’ll have to add just a little bit at a time and keep testing until you get an idea of exactly how much you’ll need with your tap water, and the nutrients you’re using. After 1-2 times this step will only take seconds!
- It can be helpful to make a note of the total amount of pH up/down added. The total amount of used pH up/down will be about the same each time. Remember that number and write it down! It will make pH’ing easier in the future! The amount will change a little depending on which nutrients your plant is getting for its current stage of life, but having a ballpark figure is really helpful.
Unfortunately there’s no exact formula to adjusting pH, because factors such as the source of water, growing medium, nutrients, drainage and growing setup all have an effect on pH.
You will need to use trial and error to figure out what amount of pH Up or Down works for you in your setup with your nutrients.
If you’re new to adjusting pH, start small with pH Up and Down, and only work your way up to bigger amounts after you’ve gained some experience. Most growers will be able to figure out their personal measurements within 1-2 waterings.
The very first time you pH your water, it will take a little trial and error to figure out how much PH Up or PH Down to add to get to the right number, since everyone’s water is a little different. The general idea is to start with a little bit, maybe a few drops, then retest and add more if needed. Continue this until you get the water in the proper range. PH Down is much stronger than PH Up, so be extra careful with PH Down! After the first time, it will be much easier to measure out how much you need.
Tips for Cannabis Nutrient & pH Management:
Don’t Go Overboard: With liquid nutrients, it’s usually better to give too little than too much. You can always add more, but it’s harder to take nutrients back. A good rule of thumb is to start out at half the recommended dose, and only raise nutrient levels if the plant needs it.
Never Mix Nutrients or Supplements Directly With Each other: Always add nutrients directly to your water. It’s bad to mix nutrients together. They can react with each other in a way that can make nutrients less available to your plants. Most nutrient bottles or pH adjusters will come with a clear warning that says the same thing. Always add any additives directly to the water – your plants will thank you for it.
Add “Micro” to Water First – If you’re using a 3-part nutrient series with a bottle for “Micro,” you should always add that to the water first. It will also say so on the bottle and on the nutrient schedule, but just something to be aware of.
Tap Water Can Be Easier to pH Than RO or Highly Filtered Water: Tap water or mineral water has an extra buffer of extra minerals and other “stuff” in the water. This helps prevent the pH from swinging up too high or too low quickly and can make pHing easier. RO water has very little buffer (it’s basically pure water) and tends to swing up and down in pH easily with just a little pH Up or Down. Do you need special water or is your tap water good enough?
Shaking Water Changes the pH: When checking and adjusting pH, some growers like to shake their water container to make sure everything is evenly mixed. This works well, and roots love the extra dissolved oxygen, but it’s important to understand that after shaking the nutrient water for a long time, the additional dissolved oxygen will raise the pH of the water. Don’t worry about this – don’t retest then readjust the pH. If you’re going to hand-water to your plant, you want to make sure you go by the pH of the water before it was shaken up. In hydro, the water is going to be oxygenated anyway, so shaking it before testing is ok. If water is allowed to sit for a while, it’s normal for the pH to change a bit. When it comes to mixing, make sure you mix water gently so nutrients and pH Up or Down are evenly distributed, but avoid vigorous shaking until after you’ve already adjusted the pH.
pH Drift is Normal. Try to keep pH in the suggested range and you’ll be fine, even if it’s on the higher or lower end of the scale.
Soil or Soilless Mediums
Next time you water the growing medium, test the pH of the water going in
Test the pH of the water that runs out of the bottom (runoff water)
If the pH of the runoff is in the right range, even if it’s not the same as the pH you put in, you’re good. If the pH of the runoff water coming out is too high or too low for your range, you know that you’ll need to correct the pH.
Test the pH of the reservoir by taking a small sample of water and use it to test the pH.
If the pH is outside the 5.5-6.5 pH range, you know you’ll need to correct the pH.
Think about the pH of the water that you watered your plants with. You made sure it was in the right range. So if the pH that comes out the bottom is outside the range, that means you need to either raise or lower the pH to get it back where it should be.
Flushing– pH problems are sometimes caused by over-fertilizing (the plant was given too many nutrients or supplements, which builds up salts in the growing medium). If you believe this is the case, flush the growing medium to remove salt buildup. This should only be done when the regular method isn’t working for you, and/or you have no other choice. Flushing means giving your plants 1-3 times the volume of its container with plain, pHed water. The flush leaches out extra nutrients and salts. After the flush, water plants with a light nutrient solution. It’s normal for plants to droop when they’ve been flushed (showing signs of being overwatered), but the drooping will go away as soon as the medium begins to dry out. After the top inch of growing medium has dried out, water the plant as normal and test the runoff water to see if the pH has corrected itself.
- 6-7 pH – in the right range, no changes needed.
- Less than 6 – provide next watering at pH 7
- More than 7 – provide next watering at pH 6
Continue this formula with each watering.
Water going in should be 5.5-6.5 pH
If runoff pH is…
- 5.5-6.5 pH – in the right range, no changes needed.
- Less than 5.5 – provide next watering at pH 6.5
- More than 6.5 – provide next watering at pH 5.5
Continue this formula with each watering.
Maintaining pH is especially important in hydroponics. Luckily it’s really straightforward since you only have to worry about the water in your reservoir. However, if the pH is off in between reservoir changes, you can make adjustments.
If pH is too high, add a tiny amount of “PH Down” solution to your reservoir (a little bit goes a long way with PH Down). Return to reservoir and check pH again in a few minutes.
If pH is too low, add a small amount of “PH Up” solution to your reservoir. Return to reservoir and check pH again in a few minutes.
Tips for Hydroponics Growers
- The pH of the water tends to go up when the water is oxygenated (for example by adding bubbles or shaking water) – this is normal.
- The pH also changes as plants use up nutrients in the water
- It’s a good idea to completely change your reservoir at least once every 1-2 weeks, especially in the flowering stage when plants are more picky. This constant renewal helps prevent a lot of pH problems as well as nutrient buildup in the reservoir.
- Test reservoir water regularly so you spot any pH problems before they damage your plants.
If you’ve recently adjusted the pH of your growing medium or hydroponic setup, or made any other major changes, it’s important to keep testing pH regularly.
The most common way to test for the pH of water is probably using drops or strips. These work by taking a water sample, and you compare the color produced to a chart. These give you a rough idea of the pH.
Digital pH pens look a bit like a thermometer. Basically you dip the end into your water and a digital readout on the screen will tell you the pH.
They each have their pros and cons, so it’s important to figure out which one works better for you.
PH Strips or Drops
- Not as exact as a PH Pen
- Some people don’t like using a color chart
- It can be hard to read the color in different colored lighting
- Harder to use if you have dark nutrients that stain your water
Digital PH Pen
- Get an exact reading of the pH on a digital screen – no comparing to charts or other guesswork
- Very quick and easy to test – just dip the pen into the water for a few seconds and the pH will show up on the screen
- Can be easy to break – always put the cap back on after use!
- Needs to be stored properly – always put a few drops of storage liquid in the cap before putting your pen away or it will stop working
- Needs to be calibrated every grow or so just to make sure it’s staying accurate
- Expensive compared to drops/strips – Requires purchase of not just the PH Pen (which can be pricey) but also 3-4 separate fluids for storage and calibration. That being said, once you’ve purchased everything you’re set for many grows.
This type of pH Test Kit works by using drops or strips that turn a color to reveal the pH of your water, using a color chart. Basically you take a small sample of water in an included test tube, add a few drops of the pH solution or dip the strip, and then match the resulting color to figure out the pH.
Many pH Control Kits come with pH Up & pH Down included. Even though they’re often sold by “General Hydroponics,” these kits work great for soil in addition to hydroponic applications.
- Take small water sample in included test tube
- Add a few drops of pH fluid (or dip strip)
- Match the color to find the pH (compare to chart)
Adjust the pH:
- Add a small amount of PH Up to bring it up
- Add a small amount of PH Down to bring it down
How Do Digital pH Testers Work For Growing Cannabis?
Digital pH Pens offer a precise way to measure the pH of your water. No need to squint at a color chart with a pH Pen, you simply look at the number printed out on your screen.
All testers come with step-by-step directions that tell you exactly what you need to do to make sure you pH tester is accurate for years to come!
Don’t get a “TDS” or “PPM” meter by accident! It’s different from a pH pen!
PH Tester PH-009 Digital pH Meter – With 2 Pack of Calibration Solution Mixture Included – Cheap!
- You just can’t beat the price! This is one of the cheapest pH pens I’ve seen.
- Actually comes with a 2-pack sample of calibration fluid, so you don’t need to buy those just to get started the first time (though you will need to get more soon). You still need to get storage solution.
- It may not have all the bells and whistles, but it will get the job done on a budget!
Hanna Instruments HI 99104 pH Tester – this one doesn’t get rave reviews, but it’s been reliable and accurate for me for years and many grows. I have two of these (old and current model) and I still use both of them.
About the HI99104 pH Tester Model:
- The main reason I like this model is the long, thin neck. It makes it so that I can stick this directly into a 5-gallon water jug and test the pH that way. With most other pH tester pens, the neck is too thick for that, and so I have to pour some water out to test it.
- When compared against other pH tester and pH drops, this tester came out just as accurate in our tests. We actually have two, one for each grow room, so we don’t have to shuttle them back and forth.
- You’ll need to get storage and calibration solution (like every pH tester)
- Follow the directions, including use and storage – it’s pretty straightforward. The main thing is to just add a few drops of storage solution to the cap every time before putting the pen away. It’ll last for years!
Hanna Instruments HI 98128 pH Tester – this high-end tester has all the bells and whistles you could possibly want from a digital pH Tester, but may be overkill for new growers.
About the HI98128 pH Tester Model:
- All the bells & whistles
- You’ll need to get calibration solution (like every pH tester)
- Follow the directions, including use and storage – it’s pretty straightforward
All pH tester pens come with step-by-step directions that tell you exactly what you need to do to get a quick, easy and accurate reading every time! In order to make sure your pH pen stays accurate, you need to get a few extra bottles.
Calibration and Storage Fluid for pH Pens
- Calibration fluid – You get a “4.01” & “7.0” bottle together as a kit, and you need both of them to be able to calibrate your pH pen
- Storage Solution – Not 100% necessary, but it dramatically extends the life of the pen. You put a little bit of this liquid in the cap before you put your pH pen away each time. Storage solution can also be used as cleaning solution in a pinch, so if you’re just going to get one, get storage solution over cleaning solution.
- Cleaning Solution – Not 100% necessary, but it extends the life of the pen
If you don’t get all these extra items, you won’t be able to take the best care of your digital pH tester and it won’t give you accurate pH readings and they won’t last nearly as long.
There are many other digital pH testers besides the ones listed above, and many of them will work great. Just be sure you don’t actually buy a “TDS” or “PPM” meter by accident, which is different and does not actually test pH. If you want a TDS meter, that’s great, but many growers accidentally buy one and don’t realize what it’s actually for. Learn more about TDS & PPM.
What to Do After You Test the pH
After using your pH pen, you use a bottle of PH Down & PH Down to adjust the pH to where it should be, if needed.
How to Adjust the pH
- Add a small amount of PH Up to bring it up
- Add a small amount of PH Down to bring it down