4 feet between the trees, 6" from bottom limb of tree to ground x 2 = 5 feet.
I also plan to put a connector between the trees to make setup easy. (the "input" for each tree will have the extension with the "output" connector being right after the last node in a given tree)
Why do that?
It only requires two 50 foot runs of Cat5 across the yard to cover all 12 trees

It also removes all hazardous voltages from the "first line" of lighting...
The other options are:
- 12 runs - one per tree
- 120v AC power run + one Cat5 + one hub + 12 shorter Cat5 runs.
If I can only get away with 3 feet between nodes, I may just put a stray pixel between each tree to regenerate the signal...
RM