I replanted last years Dahlias (Boom Boom Red Pompom and Santa Claus Decorative) earlier in the year in April. I started them off indoors to give them a head start. It was the first time I’d tried it and it didn’t work too well. The plants grew very tall and spindly. I wasn’t brave enough to pinch all the shoots as I wasn’t convinced they’d flower. I did eventually pinch them, which did produce more shoots and flowers.
Here are some pics. Note Santa Claus has never grown red & white, it has always grown a faded orange version. No idea why?
See my previous post about starting them indoors: