why have my Berberis Thunbergii lost all of its leaves?
By Gena
United Kingdom 
the few leaves that remain or dry and crispy, it was beautiful and very healthy looking when i bought it 6 weeks ago. it is still in its pot as i'm not sure where to plant it.It is situated in a corner near a wall on my patio but in a sunny position, i have watered it regularly and especially in the evenings of the past few very hot days.
3 Jul, 2009
Answers
Check for berberis sawfly as well. Thunbergii is more likely to be attacked by them than other Berberis. Like rosemary beetles they can do a fair amount of damage.
http://www.rhs.org.uk/Learning/Research/Projects/berberissawfly.htm
4 Jul, 2009
Sounds like drought, even though you've been watering, and the sun has been very strong, so has probably scorched the leaves. As it is in a pot, it's been unable to cope with the strong sun and possibly lack of water. If you're not sure, turn it out of its pot, check how dry the rootball is. If it dried out completely, and then you watered it, the water may well have just run straight through and not been absorbed by the roots.
3 Jul, 2009