Answer: If similar plants are doing well in similar light exposure, I'd suspect the soil isn't quite right for the non-blooming impatiens. Perhaps it doesn't drain as well, or maybe the pH is different. Are there roots from other plants nearby that might be competing with the impatiens for moisture and nutrients? I'd investigate further, even to the point of digging one of the plants up and transplanting it to another area of the garden. If it thrives, the soil in the old spot is suspect. If it continues to act as the others, it may be nearing the end of its natural life. Wish I could offer more insight!
Q&A Library Searching Tips