ivy's are designed to grow in scenes with real-world scale !!
 ivy's don't look that nice on a 500m tree... so, try to use this max-feature...
 growing an ivy is actually as easy as writing a plugin :))
 it's even more easy if you read what's written below...

  1) plant an IvyRoot
  2) hit the "Grow" button
  3) watch it growing in your viewport
  4) stop growing by hitting the "Grow" button again
  5) a Multi/Sub-Object Material is already assigned for mapping your ivy
  6) want a grow-animation ? - set keyframes for the ivy age

 additional notes:

 ivy's shouldn't grow on windows, correct ?
 to inform the ivy of such situations you have to freeze your window-meshes
 this way such a frozen mesh will still be used for collision-detection,
 but the branches will die there faster than on unfrozen meshes
 if you have a modifier applied to an ivy you won't see it growing in viewports (no mesh is generated while growing)

 to speed-up growing:

 - turn off "Use Selection Brackets"
 - hide all objects where it won't grow anyway, too much faces in your scene will slow down the grow-process
 - whenever possible split big meshes into some smaler ones, but having 10.000 objects also doesn't help much :)
 - disable all modifiers you might have on top of an ivy-object

 if the ivy isn't growing the way you want, you can stop growing any time,
 adjust age and/or grow-params and start growing again

Home page http://www.guruware.at/main/index.html