Yes, it’s beneficial to fertilize Plumeria even when it’s blooming. Flowering requires a significant amount of energy and nutrients, so providing a balanced fertilizer during the blooming period can support the plant’s needs and prolong the blooming season. Fertilizers with a slightly higher phosphorus content (the second number in the N-P-K ratio) can promote more abundant and vibrant flowers if used as a foliar feed at the beginning of the blooming season. However, avoid fertilizing too close to the end of the growing season, as it may stimulate new growth that could be susceptible to frost damage in colder regions.