Hi Begonia,

I have never grown Mandevilla, but I have the impression from a little googling that your Mandevillas would prefer more sun to bloom more. For example, see this link, Grow Dipladenia and Mandevilla in Containers

Technically, Mandevilla is not an annual, but who is counting?

ZM

Thank you, zen-man!

In the link you provided I found this:

For a consistent production of flowers, don't transplant your dipladenia
into a container that is too large. If you do, it won't hurt your
plant, but it will spend more energy producing roots and top growth than
flowers. You may see fewer flowers until the roots have hit the bottom
of the pot.

I now for sure this thing didn't reach the bottom of the pot - so I have a feeling this was the problem.

The container was huge for the original plant size - as it came from the nursery; but I did it this way because I wanted it to grow very tall so I thought it would need serious root system to sustain such growth.

Grow it did - but I had no flowers.

I will do it differently next year.

Thank you!

Mine didn't grow much and didn't flower much. I hear they like shady feet and sunny head. I think I must've given them shade up to their knees. I dug it up and have it in my sunny unheated basement. Doing great so far! Will get it in a much sunnier spot next year.