How To Fix And Prevent Nutrient Lockout


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Nutrient lockout is when the soil medium being used is oversaturated with nutrients. It is one of the most common problems growers face, especially when chemical fertilizers with high salt contents are used in the soil medium. Flushing is the most common way to treat nutrient lockout, and feeding is paused to prevent overloading the soil medium with excessive nutrients. Maintaining a proper pH level is key to avoiding nutrient lockout, as nutrient lockout increases if the pH value fluctuates outside the optimal range.

One of the most common problems growers face is nutrient lockout (or nutrient lockup). When growing plants inside, whether it be an indoor garden like a greenhouse, grow room, or grow tent, there are certain factors to consider, including the risk of nutrient lockout, the signs/symptoms, and if nutrient lockout can have long-term effects on your plants. 

Nutrient lockout is a challenging issue, and quite frankly, it is irritating. The good news is, nutrient lockout issues do not have to be the end for your grow room.  

By identifying nutrient lockout early by knowing the signs, knowing how to fix it, and how to prevent it, you can save your plants.

What Is Nutrient Lockout?

A nutrient lockout can be very frustrating when growing plants, especially if you are a newbie grower and have no idea what’s causing your plants to have stunted growth and yellow, limp leaves. 

When a plant experiences nutrient lockout, the plant no longer can absorb nutrients from the growing medium, and therefore, the nutrients are locked out from entering your plant’s vascular system.

Nutrients are needed for your plant to remain healthy, so if you experience a nutrient lockout, your plant is essentially being starved. Consequently, nutrient lockout leads to nutrient deficiency or in severe cases, plant death. 

Cannabis Nutrient Lockout

Nutrient lockout and nutrient mobility are key concepts related to successful growth, and growing healthy cannabis plants. Nutrients must be available for the cannabis plant to uptake from the soil.

When growing cannabis, nutrients are absorbed into the root via osmosis. If the soil medium or water has a high concentration of salts around the root zone, the plant can leach nutrients from the roots back into the soil medium. This is all due to nutrient lockout, which if not addressed quickly and monitored using a pH and electrical conductivity (EC) meter, nutrient deficiencies will rapidly follow the lockout.

Knowing the symptoms and causes is the first step to treating the problem and reversing it.

What Causes Nutrient Lockout?

The two main causes of nutrient lockout are issues with your medium’s pH level and nutrient imbalance. 


The importance of proper pH when growing plants is critical, as the risk of nutrient lockout increases if the pH value fluctuates outside the optimal range. While nutrient lockout has many causes, which we will go into later on in this article, one of the most common culprits is incorrect pH levels.

The optimal range for plants is commonly called its “sweet spot”. It is the pH value for growing high-quality plants where nutrients can be sufficiently absorbed, and nutrient deficiencies are not a problem. 

The optimal pH range for most indoor plants is 5.5 to 6.3. Therefore, pH levels below pH 5.5 or higher than 6.3 can lead to many nutritional issues, including nutrient lockout.

If the pH of the soil or grow medium strays too far from the optimal pH range, certain nutrients are absorbed over others. 

Let’s put this into perspective… 

If the pH value is 5.0, iron and manganese are readily absorbed, while essential nutrients like calcium and magnesium are not, and therefore, the plant will typically suffer from calcium and magnesium deficiencies.

pH Lockout Chart

As pH and nutrient availability play a critical role in preventing nutrient lockout, you should follow the pH lockout chart. The chart includes 17 nutrients that are essential for the overall health of your plants/crops.

Nutrient Imbalance

As plants grow, they must absorb nutrients from the soil, water, and surrounding environment. Over time, the growing medium can accumulate excess nutrient salts, which cause a nutrient lockout. 

If the salts react with your plant and nutrient solutions (chemical fertilizer) that you supply, excess nutrients (typically with a high salt content) can bond together making them unavailable for your plant, essentially locking them out for your plant to utilize. 

So, too many nutrients cause the pH to change and therefore, nutrient lockout to occur.

Can Overwatering Cause Nutrient Lockout?

As overwatering plants increase the number of salts in the soil medium, overwatering can contribute to nutrient lockout.

Can The Use Of Hard Water Cause Nutrient Lockout?

Water sources that contain high levels of water harness will lock out key nutrients required for plants to grow. Water that has high hardness, such as tap water, is also linked to scaling on equipment. This is because calcium and magnesium levels are greater in tap water compared to reverse osmosis (RO) water. 

Nutrient Lockout Symptoms

You should know the signs and symptoms of nutrient lockout to act quickly before it drastically affects your plant’s health. If your plants are suffering from nutrient lockout they may show one or more of the following signs:

  • Stunted growth 
  • Yellowing leaves
  • Curling leaves 
  • Limp and lifeless plants
  • Sometimes leaf burn

The trouble with identifying what is wrong with your plants is that the signs of nutrient lockout are very similar to general nutrient deficiencies. For example, you could be overwatering or underwatering your plants, and they may show the same symptoms of nutrient lockout. 

To be sure it is a nutrient lockout, check the pH level of the soil medium, the water supply, and the nutrient solution you use. 

If after testing, the pH level is above 6.3 or below 5.5, the pH level is the issue. But if the pH seems fine, yet your plants are experiencing the above symptoms, you may be overloading your plant with nutrients, and therefore experiencing nutrient lockout.

To accurately measure the pH in soil mediums, we recommend preparing the following:

How To Fix Nutrient Lockout?

Nutrient lockout is an annoyance, but it can be fixed. So, identify that nutrient lockout is the problem for your plants, and follow the steps outlined below to fix the issue. 

The first step to fixing nutrient lockout is to stop feeding your plants. As mentioned, overloading your soil medium and plant only pumps them with more nutrients, which worsens nutrient lockout.

Next would be to flush your plants with pH-balanced water. The best way to fix nutrient lockout is to flush the plant to clear the soil/growing medium from excessive salts. Flushing is the most common way to treat nutrient lockout, by flooding your plants with water in the hope to wash out and dilute the minerals and rebalance the pH level by breaking up salts. If you are growing in a hydroponic system, you should use a fresh solution. 

After flushing the soil, allow it to dry out completely before you water your plants again to prevent root rot from overwatering. After the flushing process, you should no longer have issues with nutrient lockout, so, you can refill your reservoir with the nutrients and supplements your plant needs.

NOTE: Flushing should not be used if your plants are already suffering from nutrient deficiency. Flushing them during this time will reduce their growth and resin percentages.

How To Prevent Nutrient Lockout?

A nutrient lockout can be fixed, but as always, prevention is always much better than a cure. To prevent a nutrient lockout, your focus should be on keeping nutrients balanced and the ideal pH ranges stable. Here’s how to prevent a nutrient lockout.

Regularly Check & Maintain pH Levels

Imbalances in the plant medium’s pH level are one of the leading causes of nutrient lockout. The pH levels should be tested weekly, if not bi-weekly, to make sure your plant is growing in the healthiest environment possible. 

A pH meter is an inexpensive and highly-accurate tool to keep an eye on your pH levels. This means any issues with the medium’s pH can be adjusted before a nutrient lockout occurs. 

If the pH is off, you can buy a pH adjuster to increase or decrease the soil’s pH level. They are super easy to use and are available online. 

If you have a hydroponic system, we also recommend investing in a pH controller to monitor the pH levels more closely and add acid or alkaline solutions as needed.

Use Organic Fertilizers

Organic fertilizers usually have lower mineral and nutrient levels than chemical fertilizers. This means organic fertilizers are less likely to cause nutrient lockout and they also benefit your plant’s overall health.

If you would prefer to use synthetic fertilizers, ensure they contain good quality nutrients, and keep a close eye on the pH level and the number of nutrients that are supplied in every watering. 

Regularly Flush Your Plants & Flush With Reverse Osmosis Water

In addition to a nutrient lockout fix, regularly flushing your hydroponic system and growing medium is a great way to prevent the problem.

Flushing is recommended at the end of each growing season to check your plant is absorbing the nutrients they need to grow and thrive. This is particularly important if you have potting soil. Potting soil is usually stripped of nutrients at the end of the growing season, so flushing will re-feed your plant’s soil before the next harvest. Some growers choose to compost the potting soil and start with freshly-bought soil to prevent a nutrient lockout. 

When flushing your medium, use pure water such as pH-balanced water or RO water to guarantee purity. The use of RO water makes it easier to maintain and adjust the pH level of the growing medium, because you have more control over the water chemistry

If you wish to adjust any nutrient levels, you may also want to flush the plants as the pre-flowering stage is a great time to flush the plant’s medium. This means the soil will have a neutral pH level, and therefore, the chances of nutrient lockout are reduced. 

If you are unable to flush your soil’s medium, a filtration system using RO water can be used. 

Summing Up, Nutrient Lockout

Nutrient lockout is a nuisance, but it doesn’t mean the end for your plants. If you haven’t managed to prevent it, there are ways to fix nutrient lockout if you catch the signs and symptoms early.

The bottom line comes down to how well you maintain and manage the pH level and avoid nutrient imbalances. This includes supplementing the right nutrients and keeping the pH level within your plants’ “sweet spot”. 

If you have any questions regarding nutrient lockout or are unsure which testing tools you need, do not hesitate to contact the world-class team at Atlas Scientific

pH Probes & Sensors

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