The answer to 'why is my drip edge algae growth' is that algae growth on the drip edge of your roof is a common problem caused by moisture, shade, and organic debris. Drip edges are susceptible to algae buildup because they are often in damp, shaded areas where algae can thrive. This can lead to unsightly discoloration and potentially even damage to the roofing material over time.
The best solution is to regularly clean and maintain the drip edge to prevent algae growth. This can typically be done as a DIY project, but for more extensive or recurring issues, it's recommended to have a professional roofing contractor inspect and treat the problem.