I also think that the sub-categories would work nicely. In fact, a category tree would be the most user-friendly thing. For example, growing/casing/birdseed/cyanescens, etc.

I am almost positive you could find a free Java applet that would do the tree for you. All that is needed is to actually decide what goes where.

This would also solve another problem. Whenever I want to see the new pictures, I have to download a million old thumbnails to get to them.

A good temporary solution would be to put the newer ones at the top of the page. Or to have a "new" section, with cross-links so they also appear in "growing" or wherever they belong.

P.S. Night Child, you da man!