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What Is Nutrient Lockout and How Does It Affect Cannabis?

One of the most common problems faced by indoor cannabis growers is nutrient lockout. Sometimes referred to as “lockup” or simply “lockout,” nutrient lockout is a common occurrence, but one which can leave a beginning grower scratching their head and wondering just what happened to their plants.

Often misidentified as a nutrient deficiency due to the corresponding symptoms, nutrient lockout can be difficult to identify correctly. Fortunately, once identified, the problem can be reversed, and the plant reinvigorated so long as it is handled in a timely manner.

What is Nutrient Lockout?

Nutrient lockout occurs when a plant’s roots and growing medium become overly-saturated with excess chemical nutrients and fertilizers. Because many nutrient lines (especially hydroponic nutrients) are salt-based, these salts can accumulate in your plant’s root zone or in the growing medium. An excessive buildup of salt-laden nutrients can cause nutrients to bind to one another and lead to your plant’s inability to uptake the nutrients provided by the solution through its roots.

As a result, the plant cannot use the available nutrients, despite continued feeding and watering. Continued feeding during nutrient lockout can actually make the problem much worse. Hydro grows, especially those utilizing coco coir or Rockwool mediums, are especially susceptible.

How to Identify Nutrient Lockout in your Cannabis Plants

Nutrient lockout can be challenging to detect and properly identify because its symptoms so closely resemble a nutrient deficiency. Symptoms typically include:

  • Weak, flimsy stalks
  • Droopy, discoloured foliage
  • The appearance of being underfed
  • Stunted growth
  • Yellowed or yellowing, curling leaves

It is easy to see how nutrient lockout can be mistaken for a nutrient deficiency. This common misidentification leads many growers to increase the levels of nutrients in their solution, in turn making the problem worse. It is essential to take several proactive steps to identify and prevent nutrient lockout before it devastates your plants.

Causes of Nutrient Lockout

Though the chemical reactions occurring within the root system and growing medium are responsible for nutrient lockout, it is often the grower’s actions that lead to these conditions. The most common causes of nutrient lockout are overfeeding and improperly-balanced pH levels.


The temptation to overfeed cannabis plants is one with which many beginning growers must come to terms. While most base nutrient lines supply the necessary macronutrients—nitrogen, phosphorous, and potassium—supplemental nutrients offer up the necessary micronutrients, such as calcium, iron, zinc, magnesium, manganese and copper.

When supplementing nutrients for your plants, it is imperative to remember that more is not always better. Unnecessarily-high nutrient levels may lead to a plant’s inability to uptake other nutrients, leading ultimately to a deficiency. In much the same way that performance athletes avoid overeating for fear of a sluggish performance, you should avoid overfeeding your plants, as the excess could lead to a slower, less-productive grow.

pH and Nutrient Lockout

Another critical component in identifying and curing nutrient lockout is determining the pH of your water source, growing medium and reservoir’s nutrient solution. A pH range of 5.5-6.5 is ideal for hydroponic systems, while soil grows prefer a pH of 6.0-6.8. Within these pH values, plants are capable of up-taking and utilizing the greatest amount of nutrients available. In an acidic or alkaline environment, the uptake of nutrients can slow or cease entirely.

When the pH level of the growing medium or nutrient solution rises above or slips below the desired pH, nutrients become unavailable to plants and remain instead suspended in the root zone or growing medium, leading to the buildup. This buildup of nutrient salts is toxic for your plants and will lead to more significant problems if left untreated.

Treating Nutrient Lockout

The good news about nutrient lockout is that it does not necessarily mean the end of your plants. Plants can often be reinvigorated and brought back from the brink of disaster with relative ease.


The most common cure for nutrient lockout is a good flush of the root zone with pH-balanced water. Running buffered, plain water through the growing medium will help to dissolve some of the salt buildups and free up the nutes present. Many nutrient companies offer a “flushing solution,” a chemical additive that helps to accumulate excess salts as it works its way through the plant and medium, taking many of the excess nutrients with it into the runoff.

An important consideration before flushing is the water being used to conduct the flush. The water’s pH should be adjusted to meet your system’s needs and should also be checked and adjusted when mixing nutrient solution.

Many growers invest in Reverse Osmosis (RO) filtration systems to ensure the water they feed their plants is as fresh and clean as possible. An RO system can reduce particulate concentration in water (measured as parts per million, or ppm) by as much as 90-95%. RO systems filter particulate out of water and provide a consistent pH level for the grower to work with, reducing the need to buffer the pH up or down.

Flushing your plants is not without its own set of dangers as well. For example, a solid flush will essentially clear the root zone of most built-up nutrient salts, leaving the roots in a non-nutritive medium. Therefore, nutrients need to be reintroduced to the medium, but not before the medium has been allowed to dry. Feeding too soon after flushing could cause excess moisture to accumulate around the roots, eventually leading to root rot. Once your plants have been flushed, feeding can resume according to schedule.

Cannabis plant with yellowing leaf due to nutrient lockout

Tips to Avoid Nutrient Lockout

If you’re already fighting with nutrient lockout, you know all too well that prevention is the best strategy. Following a few simple steps can significantly reduce the chances of encountering nutrient lockout.

Check pH Regularly

One of the easiest methods of protection against nutrient lockout is regularly checking your grow’s pH levels. This includes the pH of the soil or soilless hydroponic growing medium, the water being used for the nutrient solution and flush, and the nutrient solution itself. Maintaining a proper pH level in all of these elements of your grow will ensure that the nutrients you add will be as readily available to your plants as possible. Investing in quality water and soil pH meters is essential.

Remember, once the pH level rises above or slips below the ideal range, a plant’s ability to properly utilize the nutrients it receives is significantly compromised.


It is not necessary to wait until your plants have begun showing symptoms of lockout to flush them. Many growers flush regularly throughout the grow cycle to ensure the nutrient lockout does not occur. While this is a reasonable strategy, it is also important to remember to reintroduce nutrients promptly to avoid deficiencies. Plants will respond well to the reintroduction of nutrients after receiving a break.

Utilizing a “flushing agent” during your flushes does not hurt, either. While some growers consider this an unnecessary step and prefer to use pure water, others swear by it and won’t flush without it, citing enhanced flavours, terpenes and THC levels. You will want to determine for yourself whether you’ll need one.

Organic Nutrients

Using organic nutrients, when possible, will also help to prevent nutrient lockout. The accumulation of salts used in chemical fertilizers is most often to blame for nutrient lockout, a problem easily solved by choosing nutrients with a low salt content or avoiding chemical fertilizers altogether. Alternatives include organic compounds such as worm castings, compost or compost tea.

Nutrient lockout can be puzzling and frustrating, with proper identification being key in its treatment. Under the eye of a careful, watchful gardener, nutrient lockout can be detected and quickly reversed, but in a neglected garden, the results can be disastrous. Taking proper care of your plants, including regularly checking pH levels, flushing when necessary, and using high-quality nutrients, will undoubtedly help to abate the problem. 

Post author
Michael Richey
Michael loves to grow cannabis and write about what he learns along the way. His best friends are his dogs and marijuana.
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