The trick seems to be to concentrate on those trees from drier climates, particularly the Middle East. Even the roses, apparently very tricky to grow, seem to be thriving - even with all the neglect that I give them...
Water is the essential... I have found some nice solar water stills - pricey, but would well worth it. I appreciate that solar heating and distillation is slow, but you don't have to supply fuel... Less fuel requirements means you can allocate fuel resources better. You don't have to go out to collect firewood - and you have to chop down fewer trees. More than one ecological disaster has been made worse by people cutting down all the trees to provide themselves with firewood. As much as some survivalists might not believe that a working knowledge of environmentalism and ecology isn't essential - you have to manage your resources... And trees are more vital to survival and prepping than you might realise.