Hopeless gardener :(
 

I'm not sure what I'm doing wrong, but everything in my (walled, London)
garden flowers really early - even stuff that's supposed to be September
flowering is finishing about now. After mid-June, the only things that
really thrive are the great big thugs (a gigantic wisteria, a renegade hop
that covers everything when my back is turned) - so I buy in colour during
the summer just to cheer it up, with the result that it looks like an
inferior car boot sale. Perennials flower beautifully in years one and two,
then just produce masses of foliage in year three, giving up altogether in
year four. Depressing and expensive.

I'd be so grateful for anyone's advice or pointers to further information -
thanks in advance