Things easily get moldy during the plum rain season.
Tips
usage
Key compounds: 发霉 (to go moldy), 倒霉 (unlucky), 霉菌 (mold/fungus). The 'bad luck' meaning comes from 倒霉, one of the most common colloquial expressions.
memory
霉 has 雨 (rain) on top - moisture causes mold. The plum rain season (梅雨) sounds the same as 'moldy rain' (霉雨), which is how the season got its nickname.
Rain radical on top, the indexing radical. Mould grows in damp, humid conditions - the rainy season especially - so the rain radical pins down the cause. Files 霉 with 雪 snow, 露 dew, 霜 frost - the weather family of moisture-related characters.
Bottom 每 supplies the sound - měi shifted to méi in 霉's reading. The 'every' meaning is dormant; treat 每 as the phonetic. Same root: 梅 plum (whose ripening signals 梅雨 plum-rains, the very season mould appears), 海 sea - all sharing this graphic root.
