I'm looking for an old fantasy book. A woman/girl moves into new house and odd things happen that actually the tree or boulder in backyard is responsible for. The girl and the tree form a bond/relationship. Something about a trap room in the house and a old shed/garage with secret, golden door. The front cover was very colorful...
Prospero's Children by Jan Siegel (2001) trilogy?
The blurb seems to match nicely;
It began ages past in fabled Atlantis, when a mad, power-hungry queen forged a key to a door never meant to be opened by mortal man--its inception would hasten her own death and the extinction of her vainglorious race. For millennia the key lay forgotten beneath the waves, lost amid the ruins of what had been the most beautiful city on Earth. But however jealously the sea hoards its secrets, sooner or later it yields them up. Now, in present-day Yorkshire, that time has come. And for young Fernanda Capel, life will never be the same again . . .