It’s a persistent rumor in the cannabis world—white ash is a sign of a superior product. Black ash, according to this thought process, is a byproduct of an improperly flushed or cured plant.
Is this true? Let’s discuss.
White vs. Black Ash
Finding value in ash color isn’t unique to cannabis smokers. In fact, many believe that the trend of associating white ash with a high-quality smoke began with cigar smokers. This is because ash color is related to mineral content, with a higher mineral content leading to white ash. Cuban tobacco was grown in mineral-rich fields, so smoking a Cuban cigar was more likely to lead to white or grayish ash.
Despite the urban legend, cannabis ash color has little to do with flushing or curing the plant. Instead, the color is impacted by the burn temperature, the burn length, and the mineral content. Yusiharni and Gilkes  note that combustion temperature of plants plays a key role; carbon-based charred material decreases alongside nitrogen as temperature increases. “Dark colored (black) ash contains higher amounts of charred organic material compared to the light-colored ash that is mostly composed of crystalline or amorphous inorganic compounds.” 
Tobacco sellers who wanted white-ash products used to add magnesium or calcium carbonates, nitrates, and acids. When burned, a metal oxide formed, coloring the ash white.
It’s possible that dry cannabis leads to white ash because it’s associated with a higher burn temperature.
Ultimately, you can’t tell much about the quality of the cannabis you’re smoking by the color of its ash. There are many factors that affect plant quality, however. These include cultivation style, grow conditions, and manufacturing, among others. Certificates of analysis are a more appropriate metric for flower quality.
There are myriad factors that can affect a cannabis plant’s quality, and white ash seems to have little to do with most of them.
- Yusiharni E, Gilkes R. Minerals in the ash of Australian native plants.2012;189-190, 369–380.doi:10.1016/j.geoderma.2012.06.035. [Impact Factor: 4.848; Times Cited: 16 (Semantic Scholar)]