how and when should delphiniums be divided?

Question

my delphiniums are too crowded and need to be divided,

Answer 1

Typically these are too short lived to consider dividing, but if they need thinning out, then that is better than letting them over crowd. Consult this artical for more information: https://www.gardeningknowhow.com/ornamental/flowers/delphinium/growing-delphinium-plants.htm