I've looked all over the place for info on these trees. The general info I've found (found to be inaccurate) suggests it takes 1-6 hours and a 20 block radius around the tree to grow; this is all bullocks.
A 20 block radius helps you grow a FULL TREE, but isn't necessary for the growth as we have several players on my server growing them about 10 blocks apart. Additionally, sometimes it takes days, even with world anchors and extensive player activity around the saplings.
Theories:
We are beginning to believe that jungle rubber trees ONLY grow when another somewhere is cut down. We believe that there is some kind of limit determined by rendered jungle chunks where these trees grow naturally.
How we've reached this conclusion: Person A, B, and C have planted saplings. A got hers from the jungle after chopping down a tree and planted first, then shared with B and C that planted afterwards. Tree A grew for person A but not for persons B and C. Person A cut their tree down and person B's grew. B's was cut down and then C's. Once C was down another tree grew for B as A hadn't planted anymore.
This took place over the course of a week, timings are not precise, but there have been a lot of stories that seem to support this theory. 3 days ago or so a massive number of jungle rubber trees were taken down in a jungle biome, and a day or two later, 9 sprouted near another one of our players.
Then again, this could all be extremely coincidental. We are trying to do some controlled experiments, but it's taking a lot of time.
I beseech the community for some info and other experiences about these trees. I'm really surprised there is nothing concrete, and what info does exist, seems to be inaccurate.
Technical info: Running Tekkit for 1.2.5 with Safe Creeper plugin added and EE is disabled, server is a 20 slot with 1024mb of memory hosted by nfoservers.com.
I am talking about RedPower Jungle Rubber Trees. The giant ones: