Begonia Plugs

Hi All.
We purchase plugs from Gardening Driect every year and we never have any problems.However the first plugs to arrive together this year in early April were D/petunias and Begonia Super Patio Mix.After the initial 24 hours of rest we have potted them up into 9cm pots.
Now the Petunias are growing well and roots are coming out of the pot at bottom.However the Begonias have hardly moved and around half dozen have had their leaves fall off.I was talking to someone today who purchased Begonia plugs from another source and his are nearly 2 months old and he is having same problems.Some have reached 6 inches yet a lot are still around only 3" inches tall and some leaves falling off leaving stalks.
Not sure if it is a "bad" year for Begonias or they are naturally slow to grow.Must admit as yet not done a google search about growing Begonia plugs but has anyone got any info please.I naturally presume you keep them well watered especially as there are in the greenhouse but the other chap thinks they have to be kept more on the dry side and not to get the leaves wet!!.
Thanks in advance for any answers.

 

Tottaly agree with Shiney
Dont over water and shade from strong sun until they grow , so water in the morning only, its still only April they will romp away soon maybe give them a very weak feed mixed in the water..
Spruce

 

Agree with everyone else .. Light on the water and not in direct sunlight .

Dave