The chemicals are plant growth regulators. (PGR's)
My grandmother kept her plants in her big tall drafty windows year after year, always in the same place, never moved or even rotated. Those windows were probably 8' tall, and some of the plants were that tall too.
Her Christmas cactus were always spectacular because she went to bed so early, and there was only natural light in the house year round!
She was exceptionally frugal with her heat, too, so the plants lived with chilly nights. In the summer, they grew stronger because the breeze from open windows made for thicker stems. Her cane begonias were so tall and beautiful, and I am proud to say I still have some that were grown from cuttings from her plants.
I kept begonias and geraniums in my classroom for years because my room had big drafty sunny windows.
