Hi Guest. Of the few of mine which survived (9 out of 16 plugs) one of them is just in bud. The others are growing quite well but like you say are very slow. I think others are having the same problem as I've seen a few questions similar to yours. We'll just have to be patient I suppose...:o)

I have some begonia plug plants which are now doing quite well. I also have some begonia tubers which I bought, and they are moving even slower, some way behind them. And I have some begonias recently bought from a garden centre, and they the biggest of all at this stage, ahead of the others. The progress of bought plugs seem somewhere in the middle. Perhaps an increase in temperatures will get them moving better.

Hi, it seems that everyone is having the same problem this year with begonias this year.
I bought 100 plus medium sized trailing plug begonias which arrived in late April, I have nurtured them with loving care and they are just starting to flower but some are still very small and I can fit them in the palm of my hand.
I also bought 12 large tubers from a local garden centre and they are massive plants now but struggling to flower.
My local pub has about a dozen hanging baskets full of trailing begonias all colours and they are overflowing with flowers. I don’t know what he did, wish I knew.