Nutrient lockout is pretty simple. When a plant experiences lockout, it becomes no longer able to intake the nutrients that it is being fed. The nutrients are literally being locked out of the plant.
This problem usually occurs as a result of a chemical reaction between the growing media, nutrient solution and the plants themselves. When your plant continuously absorbs nutrients and water, over time your growing medium can accumulated excess salts and other substances from nutrients.
When there is too much buildup in your medium, it can react with your plants and the nutrients you are feeding them. When this happens, excess nutrients can clump together or become ineffective, making them unavailable to the plant.
Basically, too much nutrient build-up causes a change in the pH of your grow environment, causing a nutrient lockout.
Common signs of nutrient lockout include stunted growth and yellowing leaves, as well as leaf burn. Plants can also become limp and lifeless over time. It can even start to look like your plants are underfed, but remember feeding plants more that are suffering from nutrient lockout won’t help them take in any more nutrients, and may make the problem worse.
Similar to nutrient burn, the best way to take care of nutrient lockout is to flush your plants. By clearing out your growing medium you rinse out the built-up salts that are causing the lockout. You can use plain, fresh water to flush your medium without any nutrients until the blockage clears.
The best way to actively avoid nutrient lockout is to monitor your pH. Using Reverse Osmosis water can make it easier to adjust and maintain pH because RO water will give you more control over the pH of your water. Also, there are pH base nutrients that get your plant into the prime pH sweet spot, with less need for constant measurements of pH.
It all comes down to pH, grow environment, nutrients and the water you use. Even if you do everything perfectly, things can still go wrong and nutrient lockout can still happen. Just remember to flush completely with pure water, and monitor your plants closely until they can start accepting nutrients again.