Nutrient Burn on Cannabis Plants

How to fix Nutrient burn, aka overfeeding

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Nutrient Burn – What is it? How to fix this problem thumbnail

Hi there and welcome (back)!

Today we decided to finally cover Nutrient Burn on cannabis. This happened recently to us so we have the pleasure to share this experience with you, hope it can help out! 🙂 
For you to be aware, nutrient burn and overfeeding are the same thing, a build up of salts in the soil that result in a nutrient lockout.

Nutrient burn on Cannabis - Table of content

What is Nutrient Burn
Identifying Nutrient Burn
How to fix Nutrient Burn
How to prevent overfeeding

What is nutrient burn?

Nutrient burn, also known as Overfeeding, occurs when too many salts (nutrients) are present within the soil. This can happen if there is too much decaying matter, or when the grower has added too much nutrients within the soil.

How to spot Nutrient Burn on Cannabis?

As most ways of spotting deficiencies with Cannabis the symptoms show on the leaves. The most recognizable sign are brown spots appearing and spreading on the leaves. Let’s get into it.

What are the signs of Nutrient burn?

As usual when identifying issues with your babies the signs are on the foliage. In the case of overfeeding you will see the tip of the leaves start to turn bright green, yellow and then brown.

 

What you are observing is a nutrient lockout developing, meaning that the plant isn’t able to intake any nutrients because that soil is just too saturated.

If you don’t act, you will observe the yellowing grow from the tips towards the center of the leaf. The yellow sections will turn brown and curl up.

What are the signs of Nutrient burn?

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Confirming Nutrient Burn

Now that you have observed your plants, noticed the yellowing and browning of your tips, you have validated the fact that your plants are in a nutrient lockout, not that you have saturated the soil.
This nutrient lockout could also be due to an unbalanced pH. Let’s say your soil pH is wayyyy to low, at 5.4. At this level, you can have the perfect amount of nutrients but the plant can’t access them since the soil is to acidic.

 

In order to confirm a saturated soil you are going to want to check the EC an pH levels of your soil.

 

How to measure pH and EC levels of soil :

  1. Measure the pH and EC levels of your watering solution
  2. Slowly water the soil
  3. Measure the pH and EC levels of the run-off
  4. Compare with watering solution levels
Let’s look into each step Couple words on Electro-Conductivity : Electro Conductivity is a measure that allows you to get the levels of salts in your soil. It is a important factor for soil health. Simply put, a high EC level means that the soil has a lot of nutrients (salts), a low EC level means that the soil is poor in salts. Here is a good source about EC in  soil

Step 1 – EC & pH levels of your watering solution

First things first you are going to need to know the value of the pH and EC of your watering solution.
Using this measurement and the one of your runoff you will be able to figure out the levels of your soil and how you need to react.

pH and EC pen in watering solution
Measuring pH and EC of watering solution

Step 2 – Slowly water your plant

Now that you have your starting measurements you can [slowly] water your plant with it, as usual.

Make sure you have a tray under the pot to be able to retrieve the water exiting at the bottom.

Slowly watering the soil to flush it out
Slowly watering the soil

Step 3 – Measuring the pH and EC levels of your runoff

Let your soil drip for a while in order to allow is to humidify as much as the soil as possible. Generally you get about 20% runoff, retrieve it measure the levels with your EC and pH pen.

 

Once you have the measurements you will be able to analyse and act accordingly.
Here’s the step by step :

Water the soil and retrieve the run-off

First watering runoff in tray and glass
Watering runoff of first watering

Measure the EC and pH levels of the runoff

EC Levels of first runoff way too high
Runoff in a glass – 2.80ms/cm measured is way to high. In early flowering we are aiming around 1.7ms/cm

Step 4 – Compare solution and runoff levels

This is the point where you have all the info and you can make your conclusions.
What can we learn when comparing the readings ?

  1. The pH is not the problem : Our solution’s pH was 7.0, the runoff is at 6.8. This shows us that the soil’s pH is between 6.8 and 6.9, a bit too high but not enough to create a nutrient lockout
  2. The EC levels are off the charts : Our solutions EC level was at 0.54 ms/cm and our run-off’s is at 2.80. This shows that a huge amount of salts were added to the water when it came through the soil, enriching it.
    2.80ms/cm converts to 1790ppm which is wayyy to high. Globally during the early flowering stage we should be a bit under 1000ppm.

In our case this confirms nutrient burn and that the pH isn’t the issue, we are going to have to flush.

Watering solution vs runoff

When you do this you are going to get one of 4 cases, which we will detail here to help you fix your situation. If you are in the same situation as we are you can skip right to solving nutrient burn.

EliteGarden has some great pictures that illustrate each step, you can find the 4 images below on their article that goes over this

EC measurements – 4 cases you may encounter

Case 1
EC levels of runoff are lower than the solution

EC levels in runoff lower than watering

This is perfect, this implies that your plants are taking in the nutrients.
Note: If your runoff levels are regularly very low you can start upping a little the levels of nutrients within your watering solution

Case 2
EC levels of runoff are equal to the solution

This case shows that your plant isn’t taking up any nutrients. One of the most common reasons for this is a pH level, blocking your plant for absorbing the nutrients.

Case 3
EC levels of runoff are much lower than usual

One common reason for this, especially if you are sure to have added the right amount of nutrients, is a reaction between the salts within the soil.
Check if you have small solids in your runoff, which would be a sign of calcium phosphate reacting to other salts the salts, solidifying them and making them unavailable (nutrient lockout).

Case 4
EC levels of runoff are higher than solution

This is the type fo reading you get when overfeeding. The higher ppm within the watering solution shows that there is a salt build up and it was released into the water.
In this case you are going to have to flush the soil to dissolves the salt build up.

So now that you know that you have a nutrient build up that is creating a nutrient burn on your plant, let’s look into solving the situation

How to fix Nutrient Burn (aka Overfeeding)?

Flush, flush flush, is the key word here to fix your nutrient burn and get out of this nutrient lock out 

What does flushing your soil mean?

Flushing your soil is a term used to describe the action of passing a large amount of water through your soil.
When flushing your soil to treat nutrient burn you are flushing it in order to remove the access salts that are blocking the intake of nutrients.

 

As a rule of thumb, you have to slowly drain the soil with around 1/3 of the volume of soil in water (ie: to flush 30L of soil you will use 10L of water).

 

How to flush your soil

  • Start by watering your soil with about a third/quarter of your water and take a break. Taking a break will allow the water to spread and humidify as much of the soil as possible.
  • Measure the EC levels of your soil regularly. It’s normal to observe an increase in EC levels at first, as the water is dissolving the salts in the soil.
  • Keep watering the soil slowly until the EC levels of your runoff reach the wanted levels.

Tips when flushing

  • Make sure you water your soil SLOWLY! Since water likes to take the fastest road, it is easy to create pockets of dry, unflushed, soil.
  • Give little breaks between each watering to allow the water to irrigate all the soil 
  • Flush with plain water, don’t add any nutrients to it
  • At least during the first half of the flush you don’t need to worry about pH levels of your watering solution
  • It is normal to see the EC levels rise at first. The first rounds of water are going to release all the salts in the soil

How to prevent Overfeeding?

The best way to prevent overfeeding is holding back on nutrient supplements, especially when if you’re using newly purchased soil, as soil is generally rich, so hold back on the nutrients and watch your plant to understand her needs instead of packing your solutions. 

 

Another thing we personally do is always go on the lower end of nutrient feeding schedules to make sure to bring her at least what she needs. We will then up the nutrients once in awhile to boost her growth.

Most Common Reasons for overfeeding

Overfeeding, as the name suggests, is generally due to an access amount of salts (nutrients) within the soil. You could think that too much nutrients doesn’t hurt, the plant would just intake what she needs, but that’s not really what happens, when a soil is saturated the plant is not able to suck up any nutrients and a nutrient lock up occurs.

 

This happens when too many nutrients are added within the soil, either due to decaying matter or because the grower has simply added too much nutrients within the watering solution.

 

Some growers actually get to a close nutrient burn in order to get to her “maximum intake level”, but honestly our tip is to do this if you know what you are doing, or willing to lose a bit of the harvest in order to learn. 
Alright that’s it for this one folks! If you’re still struggling with this don’t hesitate to get in touch with us, we’ll be glad to help you

That’s it for this one folks, hope you found all your answers ! If not don’t hesitate to reach out 😉

 

Until next time,
be safe and grow easy

About the author

plant-lover

plant-lover

Plant Lover is Free the Tree's founder and a passionate grower of plants. Mostly from the city, I work on my computer all day so about 4 years ago, on my off time, I started growing to have some more green in my life. I never imagined I would fall in love with botany and discover so much about this plant. Since then I keep learning everyday, meeting new awesome people of our community and which keeps me growing constantly You can always get in touch with me on our Instagram!