After cutting the stems in the second week of stretching, most of the plant are now with something missing… ca? Mg? Why should I encounter this problem now ?
Well this is a critical stage of the canna plants life. It’s switched from vegetative growth to transitioning to flower, to now being done with vegetative growth and completely concentrating on production of flower. This means different nutritional needs.
Not sure what you’re seeing but your 3 pics in the last week look pretty healthy