Fertilizing plumeria with synthetic or organic fertilizers during or just before dormancy can be harmful to the plant.

Here’s why:

1. Reduced Nutrient Requirement: Plumeria plants significantly slow down their growth and metabolic activities during dormancy. This means their requirement for nutrients decreases. The plant is not actively using the nutrients for growth, so adding extra fertilizer is not beneficial.
2. Risk of Nutrient Buildup: Applying fertilizer when the plant is not actively growing can lead to an accumulation of nutrients in the soil. This accumulation can disrupt the soil’s nutrient balance and potentially harm the plant when it resumes growth.
3. Potential Root Damage: Excess nutrients, particularly in the case of synthetic fertilizers, which tend to be more concentrated, can cause root burn or other forms of root damage.
4. Increased Risk of Diseases: Over-fertilization can create an environment conducive to root rot and other fungal diseases. This is particularly problematic during dormancy when the plant’s ability to recover from stress or damage is reduced.
5. Waste of Fertilizer: Applying fertilizer during dormancy is essentially a waste of resources, as the plant cannot use these nutrients during its dormant state.
6. Environmental Concerns: Over-fertilization can also have environmental impacts, such as nutrient runoff into water systems.
7. Organic Fertilizers: While organic fertilizers release nutrients more slowly and are generally less likely to cause immediate damage, over-application during dormancy can still lead to similar problems as with synthetic fertilizers.

To avoid these issues, aligning fertilization with the plumeria’s active growing season is best. Generally, you should stop fertilizing as the plant begins to show signs of entering dormancy in the fall and resume only when new growth appears in the spring. This practice ensures the plant gets nutrients when needed and helps prevent the potential negative effects of over-fertilization during dormancy.