Growing dahlias as perennials
We live in the highlands of Papua New Guinea. Our elevation is 5,100 feet. Even though we are very near the equator, it is quite cool here year around, and our average temperature here is 12-22 degrees Farenheit.
We grow Dahlias here as Perennials. I would like to know what is the recommendation (for our kind of climate) for when to lift and divide the tubers?
My personal experience in the last 2 years is that after planting a tuber in well amended soil, it will put out a tall, first flush of flowers. When the flowers die, I cut it down to just above ground. I will then get a slightly smaller flush of flowers. I can do this a third time, and get an even smaller flush of flowers. All of this takes about 1 year. But then, if I do not dig up the tubers and divide them, it seems they no longer will produce stalks and flowers. In fact, a number of dahlia species grown in gardens here, have completely 'disappeared,' probably from not being divided and re-planted (?).
I have searched all over the internet, and cannot find a definitive suggestion as to what to do with Dahlias in a tropical climate. Some sites suggest that I would NEVER have to lift them.
Does anyone know the "rule" for dahlias in this situation?
Thank you for any help you can give!