Being possessed of some free time and an amazing immortal watering can, I spent part of the afternoon watering every last spice tree in Ix until it could hold no more. Many of the trees were in a rather run-down condition, and I'm not sure whether they had simply never been in top form or whether some very unsympatico spice gatherer had filled his spice box while ignoring the needs of the poor trees.
In any event, perhaps it would be worth offering a reminder of how to be kind to trees. (Note: any of the following could be changed in a future update.) The basic rule is 1 harvesting equals one watering. It appears to me that petting does absolutely nothing for the trees (correct me if I'm wrong), but if you harvest 6 times you should water 6 times, etc. If I'm just wandering Ur, collecting resources randomly with no specific goal in mind, I like to harvest each tree I pass twice and then water it 3 times so I leave the tree a little better than I found it. Of course if it's raining the trees will not accept water, so just harvest a few times and move on. Don't harvest any tree heavily if it's raining, as it takes a while for the tree to regenerate in the rain, and it appears that the regeneration stops when no one is on the street.
So be kind to trees and the giants will smile on you!