Are there any good gardening forums around?

But ill state what I am wanting to ask here anyway in case anyone knows.

I live on the North Shore of Auckland.  I have been trying to grow various flowering cherry trees over the last 3 years with very limited success.

I know fruiting cherry trees require chill hours that Auckland doesn't get especially North Auckland.
However my understanding, and given that every garden centre has flowering cherry trees in abundance was that these would do ok.

However, the first year I plant them, they flower beautifully, then after that, its downhill.  The leaves seem only grow at the ends of the branches, many existing branches just die.
Flowering is sporadic and not spectacular at all.

I wonder if the reason they flower so well the first season is that have wintered in a nursery in the waikato or something..so got chill hours.

Any thoughts?  I guess I am just hoping someone can confirm my suspicions that I am wasting my time due to climate reasons.