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Cannabis-Nutrient-LockoutDo the nutrients you're feeding your plants need to break in?

It may feel like it sometimes. You nurture the plants right from the start... plenty of light, water, and food. Then, BAM, your plants start getting yellow leaves and are no longer thriving. You do everything you can to revive the plants, more food, more water, adjusting light and humidity. But the issue continues. So, how do you fix it, and more importantly avoid nutrient lockout?

You're Controlling An Ecosystem.

To fix, and also avoid a nutrient lockout, you as the grower need to remember that you are controlling a whole ecosystem. In an ecosystem, there are multiple parameters that work together in tandem to be successful. You're probably already very familiar with needing to maintain a delicate balance in order to maximize yield while maintaining the integrity of the plants.

What Is Nutrient Lockout?

Nutrient lockout is when cannabis plants cannot absorb nutrients properly. They are starving even if they are given plenty of food. Funnily enough, the nutrient lockout can make your plants seem like they are underfed. This is caused by one of the key parameters of successful growth being out of whack. Remember that you're controlling an ecosystem? Cannabis needs a careful balance of pH, water chemistry, light, nutrients, and temperature in order to have successful growth and to trigger the flowering cycles.

What Does Nutrient Lockout Look Like?

As mentioned above, marijuana plants will begin to look like they are underfed. The plants themselves will start to pale in color, and look stunted. Leaves on affected plants will be fragile, and root growth could also be stunted.

What Parameter Issues Cause Nutrient Lockout


Plants can be very picky when it comes to the pH of their growth medium. It doesn't matter if they are being grown in soil, soilless media, hydroponically - each plant species has a preferred pH, and cannabis is no exception. When grown in soil, cannabis grows best between 5.5 - 6.5 pH. When grown in a hydroponics setup, cannabis grows best between 6.0 - 6.8 pH. If the growth media does not meet the plant's pH requirements, your plants will not be able to uptake nutrients properly. While this may seem like it isn't a big deal, when the nutrients aren't taken up into the plants, they don't just disappear. They stay in the growth media. This results in nutrient salt buildup around the plants and can dry out the plants.

Water Chemistry

The chemistry of the water that you are watering cannabis plants with, or use in their hydroponics system, can greatly affect the chances of nutrient lockout. Watering infrequently, or systems with water outside of the preferred pH range of your plants, can affect the growth media, and plants, negatively. While the pH of the water can be important, the alkalinity and hardness of the water can be just as important. Alkalinity is essentially the buffering capacity of the water, and hardness contributes to that. If water has little to no alkalinity, small changes to your system can have a BIG impact. pH swings would be more frequent and be harder to keep level. 

Underwatering plants can cause nutrients to build up in the growth medium as salts. Even if you are feeding the proper amounts on a schedule, they could sit in your system without enough water running through.


Underfeeding your plants will definitely cause issues, but overfeeding can lead you to nutrient lockout. Even if all other parameters are perfect, your marijuana plants can only absorb so many nutrients at once. Overfeeding causes nutrients to accumulate as salts in the growth media. This is very similar to what happens when the pH is off.


So... Besides The Visual Symptoms, Can You Test For Nutrient Lockout?

YES! Well, not necessarily directly (aka testing your plant tissue, that isn't economical for an average grow operation), BUT you can test the parameters that cause nutrient lockout to see if one of those is out of range. 

pH Testing

Testing the pH of your growth media and water/nutrient solutions will help you to diagnose if it is a nutrient lockout. Is your pH out of range? Then you may be locking nutrients out of your plants. You can use a handheld pH meter to spot-check, or use a fertigator and controller to automatically monitor and control the pH.

Click Here for More Info on pH Testing and Growth Media!

Alkalinity Testing

Alkalinity tests are not the same as pH tests. Hear me out though, they are NOT harder and do NOT have to be time-consuming. You can spot-check alkalinity using a handheld colorimetric checker or test kit, or you could titrate for it.

Get More Info on Alkalinity

Nutrient Testing

You could try and test for each major nutrient you are feeding your plants. However, it will take a lot of time and materials to do so. The quickest (and easiest) way to get an idea of the total amount of nutrients in your growth media or nutrient solution is to measure the electrical conductivity. As with pH, you can spot-check with a handheld meter.

Click Here for More Info on Nutrient Testing

How To Unlock Your Nutrients

To save your plants, work quickly and systematically. 

Step 1: 

Test the pH of your growing medium and water. This helps to narrow down what is causing the pH imbalance.

Step 2:

Check your EC or test for individual nutrients.

Step 3:

At this step, you have a choice depending on your pH and EC results. If your pH is off, but your EC is normal, then you may be able to get away with just adjusting the pH. However, if your EC is high, even if your pH is normal, you need to perform a flush. To perform a flush, first, make sure that your humidity is at 50% or less.

For soil, this involves using water that has been pH balanced to oversaturate the areas around the roots of the marijuana plants. Your goal here is to remove all of the excess nutrients that got bound up in the soil. DO NOT add more water or feed your plants again until the soil is DRY. Adding additional moisture too early can cause rot to set in. After the soil is dry, resume watering, and then you can start feeding the plants again.

For hydroponic systems, you can flush the system as well. Overfeeding can occur in a hydroponics system. Run pH-balanced water through the system and then reset the system to normal function.

Flushing may have to be repeated several times to reset the pH balance. 

Step 4:

Adjust the amount of light the affected plants are exposed to. Too much light during recovery can cause your plants to exert too much energy trying to grow instead of recovering.

Step 5:

Continue to monitor the pH of the growth medium and make incremental adjustments to keep the pH in the proper range.


Preventing Nutrient Lockout


Preventing nutrient lockout involves TESTING.

  • Get a pH Meter - NOT TEST STRIPS, test daily, and make incremental pH adjustments.
  • Likewise, get an EC meter, test daily, and make incremental adjustments as needed.
  • Using fertilizer from a store? Take a look and see what others have said about the fertilizer mix. It could be that the manufacturer's instructions tend to overfeed marijuana plants. Adjust the amount you are feeding. Organic nutrient mixes can help avoid salt buildup.
  • Keep a Detailed Schedule with Notes. This helps you to know what you did when.
  • Perform preventative Flushing. This can be done after a period of time when you had heavy feeding.

While Hanna is no longer carrying our Fertigation Systems, we're still here to support you!


Got Questions?

Are you looking to automate your crop testing? Talk to a Hanna specialist today and ask about our agriculture and hydroponics solutions. For more information regarding how Hanna Instruments can help you with your needs, contact us, at sales@hannainst.com or 1-800-426-6287.