I need help with Adam's Laburnum trees

Hello fellow-gardeners!
I have had my 2 Adam's Laburnum trees in large pots for 4 years now. They haven't grown much but it worries me that they have not flowered yet. I could not find on Google after what year they are supposed to start flowering. Besides each summer some pests manage to severely eat leaves of those trees. I spray them periodically with crashed garlic or neem oil in water. And move the pots with the trees to different parts of the garden. It does not help.
I will be grateful to your advice.

 

Probably snail damage, I find them way up in the branches of mine.
Never grown the Adam variety, I believe that is the crossed version with broom.
Also never tried pot growing either, but they are fairly large trees so I don't think it would be good long term.

 

This is a chimera or graft hybrid between laburnam and broom. Interesting because the tissues remain seperate so you get yellow and pink flowers on seperate branches.
I wonder if they would be happier planted in the ground if possible?