How To Prevent And Treat Nutrient Lockout In Cannabis

Nutrient lockout inhibits your plant from absorbing the nutrients in the medium and is caused by a nutrient excess.
Author Enzo Schillaci
22 July 2020
7 min read
How To Prevent And Treat Nutrient Lockout In Cannabis


Nutrient lockout (or nutrient lock) is caused by the pH levels when not measuring it properly, by an excessive feeding when you're giving watering your plants with a higher dose of nutrients, if you don’t take the right care your plants will start to grow slowly, show deficiencies on the leaves and ultimately die.

1. What is nutrient lockout?

Nutrient lockout is when the necessary macro and micronutrients are present in the medium but your plant cannot absorb them because the medium is saturated or because of higher (or lower) pH levels, this it can happen in all types of mediums and your plant will start signs of nutrient deficiency.


Prevent And Treat Nutrient Lockout: nutrient lockout

Nutrient lock inhibits cannabis plants from absorbing nutrients.

This is a very common problem growers encounter when using a new nutrient brand and especially when using synthetic nutrients, a nutrient lockout will inhibit your plant from absorbing the nutrients it needs to develop and it can ultimately kill your plants if you don’t find out what's wrong with them.

2. What causes nutrient lockout?

Nutrient lock can happen because of two things:

Inappropriate Ph levels

The pH level is what determines which nutrients your plant is able to absorb, that’s why it’s so important to not only check the pH of your nutrient solution but also the pH level of the medium you’re growing in.

The pH level varies depending on the medium you’re growing in and the only way to measure it is with a pH meter, so it’s essential to have one if you want to avoid problems, although you can grow cannabis without one but it will be harder to figure out what’s wrong if you encounter problems along the way.

Nutrient build-up in the medium

Because nutrients are minerals, the excess of nutrients in the medium can increase the pH level in the medium and this can inhibit nutrient absorption.

To avoid this, it’s better to use organic nutrients or really control how much and how often you feed your plants, remember than cannabis plants need a certain amount of nutrients, feeding more or less will result in nutrient deficiency.

3. How to identify nutrient lock and symptoms?

Identifying nutrient lockout can be kinda hard because the symptoms shown will be the same as when overfeeding or when there are nutrient deficiencies, like:

  • Weak plants
  • Stunted growth
  • Yellowing leaves
  • Leaves curling

 To make sure your plants are suffering from nutrient lockout and not anything else, you must first check the pH level of the nutrient solution you’re feeding your plants and the medium they’re in.


Prevent And Treat Nutrient Lockout: nutrient lockout symptoms

Cannabis plants will start to show symptoms of nute lockout and they will get worse if you don't fix it.

You need to check both of them because sometimes the nutrient solution has the correct pH but there are nutrients accumulated in the medium, so even if you’re feeding your plants a pH nutrient solution, they won’t be able to absorb them.

There are two ways to do this and how you do it depends on the tools you have available, obviously you will need a pH meter but some of them allow you to check the soil and others don’t so you can check the soil’s pH directly or measure the run-off after watering your plants.

When measuring the run-off, the pH level of the water coming out of the pot is the pH level in the soil so if it comes up too high it means the medium has a nutrient build-up.

4. How to prevent nutrient lockout?

There’s nothing extra to do to prevent nutrient lockout other than growing with caution, with these three tips and keeping an eye for the signs your plans give you you’ll avoid any problems. 

Check pH daily

Depending on the medium you’re growing in, you’ll have to check the pH daily or even multiple times a day, in hydro the roots are directly in the nutrient solution so you have to check it a couple of times a day while in soil you’ll be fine by checking the soil and the nutrient solution once a day.


Prevent And Treat Nutrient Lockout: adjust pH

Ph up and down can be used to adjust the pH level of your nutrient solution.

If you need to adjust the pH, you can buy a pH Up or a pH Down solution at your local growshop or even adjust it naturally with lemon juice (decrease the pH) or baking soda (increase pH).

Use organic nutrients

Another good way to prevent it’s using organic nutrients, and unlike synthetic nutrients, organic nutrients make the minerals available in the medium for your plant to absorb them when they need to instead of feeding the roots directly.

If  you wanna keep using synthetic ones, make sure you use good quality nutrients and always check the pH and amount of nutrients you provide in every watering, have in mind that in most cases the recommended dosage the manufacturers advise is too high, so if you don’t have a TDS meter you’ll have to decrease the dose manually.


First half of the Vegetative stage½  dose of Veg. Nutrients
Second half of the Vegetative stage1 dose of Veg. Nutrients
Pre-flowering stage½ Veg. Nutes + ½ Flowering Nutes
First half of the Flowering stage½ Flowering Nutes
Second half of Flowering Stage1 dose of Flowering Nutrients
Ripening and Harvest Flushing (water)

How to manually measure the amount of nutrients per growth stage.

You can follow the chart above to make sure you’re not overfeeding your plants, just remember that this is approximate and you should see how your plant develops to increase or decrease the nutrients.

Flush your plants

If you wanna be sure nothing happens, you can always flush between the vegetative and flowering stage although it is not obligatory but will ensure there is no excess to cause nutrient lockout when going from one stage to another.

5. How to treat nutrient lockout?

Depending on the amount of nutrients in the medium, it can take a couple of flushes to completely remove them so you will need to measure the medium until the run-off (or soil) has the correct pH, this is the only way to treat nutrient lockout, if you don’t have a pH meter then you will have to do it until your plant is back to normal. 


The best pH level in your case will depend on the nutrients you’re using, your environment and the strains you’re growing but you can use this chart as a guideline.


Prevent And Treat Nutrient Lockout: symptoms

When your plants can't absorb nutrients they will start to show deficiency symptoms.

When doing this it’s a good idea (if you are growing indoors) to decrease the humidity level in your growing space because the humidity can go up and it will stress your plants even more.

The water you’re flushing with needs to be pH’d and the right pH level will depend on the medium you’re growing in.


MediumPh Level RangeOptimal Range
Hydro and Soilless5.5-6.55.8-6.0

Optimal levels for cannabis in different mediums and stages.

6. In conclusion

Nutrient lockout can be caused by overfeeding but is really caused by the pH level of your solution and medium, this is a really common problem with new growers so make sure you’re feeding your plants properly.

If you’re dealing with this kind of problem and need advice or want to help us by giving tips, please leave a comment below!

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