So I have an image which I've divided up into layers, of a small plant. I want to scale the plant to make it grow using key frames. Problem is, when ever I try and scale the stem of the plant, the bottom of the layer doesn't have an anchor point. I tried this same technique in apple motion, and when I'd preview the animation after I'd create it, the bottom of the plant stem would never really be where it started growing from in the first place. I'm sure this is a pretty simple fix. I just need a way to anchor the bottom of the stem layer so it looks like it's grown an inch or two by the last key frame.
Mathew already mentioned the way to move the anchor point at the bottom. I would suggest that for the very last step. First animate the stem and branches/leafs forming (use masks on textured shapes created in PSD while also animating the scale for each individual element with the anchor point moved at the bottom of each one - where it connects with the previous piece). Then pre-comp and apply a Mesh Warp to create some movement as it grows - leaves start up and then rotate sideways a bit as they grow and become heavier... . After that precomp again and set anchor point at the very bottom and make the whole plant "grow" by scaling up. You would need of course to play with the timing of the animation for all elements to give it a more organic feel.
Here's an example of a tree (mid spot) that I made grow using this technique: