If you’re producing poinsettias this year, you are probably just about finished with potting up your newly rooted cuttings. Keeping an eye on your crop throughout the production cycle will help to identify problems early, and allow you to correct the problem before it gets out-of-hand. Consider this blog post your “cheat sheet” on identifying poinsettia nutrition related disorders.
Common deficiencies are more likely to appear in mid-fall, but in order to head them off it’s important to keep track of your E.C. and pH levels now. For best results, maintain a feed E.C. between 1.0 and 2.5. Higher E.C. values will allow salts to accumulate, which will inhibit nutrient uptake. High E.C. can also cause young roots to burn – which provides an entry point for root rot problems. An optimal pH is in the range of 5.8-6.2. A pH greater than 6.5 will stunt growth, and iron deficiencies will eventually occur. Bi-weekly testing of these indicators and keeping good fertility and spray records can help you to understand what type of corrective action to take if a problem arises.
As with any nutritional problem, symptom location can help to narrow down the culprits. Symptoms in the older, more mature leaves are typically caused by nitrogen (N), phosphorus (P), and/or magnesium (Mg) deficiencies. Symptoms in new or younger growth suggest micronutrient deficiencies such as calcium (Ca), iron (Fe), sulfur (S) or molybdenum (Mo). High quality images and a more extensive description of typical symptoms of these deficiencies can be found in this article.
Remember that a few single or grouped symptomatic plants typically suggest a pathogen or pest problem, while widespread symptoms suggest nutrition issues.
Interested in more general nutrition information? Check out this refresher.