There’s also a closeup of one of the hexagons. The flower seems to be one of the seven autumn grasses, and as it’s a hitoe (unlined) kimono, it would probably be worn in September. (You can see when lined/unlined/etc. should be worn on this page.)
The woodgrain shibori is likely to have been stitched rather than pale-wrapped (arashi). The main evidence of this are the horizontal lines of slightly different color, which follow where threads would have been. These wouldn’t be present in arashi:
The flowers are done in hon hitta kanoko, dots within squares. The amount of handwork it must have taken is mind-boggling.
Update: I had time to verify that the flower is specifically kikyou, Chinese bellflower, one of the seven autumn grasses. According to the Japanese Haiku Dictionary kikyou is an early autumn flower.