How To Prevent Late-Season Poinsettia Problems
November 4, 2025 In a recent e-Gro Alert, Clayton Humble, Patrick Veazie, and Brian E. Whipker of North Carolina State University cover some of the most common disease, environmental, nutritional, and pest problems that can affect late-season poinsettias. From there, the group shares its best practices to prevent such problems before they detrimentally affect the health and appearance of this high-value holiday crop.
Poinsettia Problems – Magnesium Deficiency
One of the most common nutritional issues that plagues poinsettias is magnesium deficiency. The group says that this type of deficiency “can easily develop with the use of 20-10-20 in areas that lack Mg in their water source, especially when the Mg contribution from any dolomitic limestone leaches out of the pot over time.” However, due to the increasingly more common use of wood fiber-based substrates that have a higher pH mix, with less dolomitic lime blended in, magnesium deficiency may be observed “earlier in the season due to an even lower initial Mg contribution from the lime.”
Symptoms of magnesium deficiency include interveinal chlorosis on the lower foliage of poinsettias, though later season occurrences are more likely to appear higher up on the foliage, below the bracts. Additionally, there is the possibility of necrotic spotting developing over time.
To fix the problem of magnesium deficiency, growers first must determine where a plant’s magnesium supply is coming from and if any of those suppliers are underperforming or need supplemental help. For example, one common way of magnesium being supplied to plants is through irrigation water. Therefore, it’s “important to conduct irrigation water analysis to determine how much magnesium is being supplied through the irrigation water and to supplement the remaining required magnesium with supplemental magnesium,” such as through magnesium sulfate or a fertilizer.
Poinsettia Problems – Proper Spacing
An important but often overlooked cultural practice of plant production is plant spacing. The reason why it’s often overlooked is obvious, as growers aim to maximize the number of plants per area. However, overcrowding a growing space makes it difficult to scout for problems, not to mention prompting plants to compete for light, leading to leaf loss, brittle tissue, and stretching. These problems can snowball into further health and nutrition issues, making them prime targets for pests and disease. Additionally, that leaves growers with visually unappealing poinsettias, making them a hard sell to consumers.
Poinsettia Problems – Water Management
“Water management is an important balance required to promote optimal growth,” the group states, stressing the importance of neither overwatering nor underwatering plants. Common problems associated with underwatering include leaf scorch, lower leaf loss, and marginal necrosis, while a common issue in poinsettias from overwatering is Pythium root rot.
Pythium root rot leads to desiccated roots, which in turn lead to “wilting caused by a lack of water uptake.” To determine whether or not Phthium root rot is the cause you’re combating, the group suggested the common diagnostic method of removing “the root ball from the pot” to “evaluate the roots for brown/desiccated roots.”
To help maintain a balance of water management for poinsettias, they “should be adequately irrigated up to level 4 but also allowed to dry down to a moisture level of 2 on the 1-5 moisture scale.”
Lastly, during the second half of production, the group notes that “plant biomass accumulation slows, temperatures drop, and day length shortens,” which can create conditions that lead to oversaturated root zones, requiring closer management and inspection of plants’ irrigation needs.
For additional and more detailed best practices to protect the health of late-season poinsettias, including bract edge burn from calcium deficiency and damage from whiteflies, please read the full e-Gro (Electronic Grower Resources Online) alert “Preventing Late Season Poinsettia Problems.” Additional and current e-Gro alert pieces from Volume 14 (2025) can be found online.
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