Yellowing: Some Causes, and What it Means for your Grow
Hi Guys, Dr. NPK here. People can be green with envy, red with anger (like when my football teams lose!), but most people don’t like to be… yellow? As growers, that’s the most important color we hope to not see! Leaf yellowing is a very vague term that can mean a variety of things to different people. This article is dedicated to helping you understand yellowing: why it occurs, what some potential causes are, and methods you can use to determine the cause.
What Causes Yellowing?
Unfortunately, diagnosing yellowing is extremely difficult. It’s difficult to quickly diagnose issues in your grow due to the sheer number of variables involved. In order to definitively conclude that a given variable is causing the problem, two separate trials must be identical except for the variable being tested. When solving an issue in a living environment, this is often impractical or impossible to do. Below are some of the more well-known reasons that yellowing can occur.
pH Range. In my personal opinion, incorrect pH is one of the most common mistakes people make in their grows. Many growers test the pH of their sumps, but fail to test the runoff pH as well. If there is a significant difference between the two pH’s, it’s likely that something is going awry in your medium/soil. Remember that your ideal pH is between 5.8 and 6.3.
Do be careful, however. Nitrogen toxicity is a real thing. Symptoms of nitrogen toxicity include:
- Darker leaves
- Weak stems
- Stunted growth
- A “claw look” to the leaves.
If you’ve ruled out a nitrogen deficiency as your cause of yellowing, it’s time to look at other nutrient deficiencies.
Remedies to Yellowing
Identifying the source of the yellowing is half of the battle! You’re nearly there! The next step is treating the problem.
Obviously, pH adjustment is basically self-explanatory. Use your favorite pH up/down to get to the correct pH. If your media is going bad, switch it out for some fresher material, or get some microbes to help you out.
For nutrient deficiencies, especially those unrelated to N-P-K, take a peek inside your reservoir. Do you see any precipitate (typically in the form of white, solid stuff)? If so, you may be experiencing a nutrient lockout. Nutrient lockout means that the ions in your sump are reacting with one another to make insoluble salts that just chill at the bottom of your reservoir. If you’re getting yellowing and you see a bunch of solid stuff in your tank that you didn’t add intentionally, chances are that nutrient lockout is preventing the contents of your sump from being delivered to the plant! Make sure you are mixing individual nutrients slowly and completely.
Lastly, if you have an environmental stressor or pest… address that problem first, silly!
Yellowing is a difficult issue to remedy in your grow. It is always worthwhile to take the time to ensure that your pH is within the correct range, your plant has plenty of secondary nutrients and that you are mixing you nutrient correctly to avoid making insoluble salts.
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About the Author
Dr. NPK has been in the chemical formulating business for over 9 years. With a Bachelors in chemistry from UCLA and a Ph.D. in chemistry from UC Irvine, he has always had a passion for chemical formulation. Over the past several years, his focus has narrowed towards the research and development of products that are optimized for cannabis. He assisted in the development of the Elite Nutrient line and takes great pride in the products he created and uses himself. He has made it his mission to cut through all the pseudoscience available on the web and to educate readers on the science behind growing top-shelf bud.