While some gardeners say that the polymer crystals keep the soil moist longer than without them, research on the crystals isn't clear whether they really help. There is a soilless mix that contains rock wool, which holds water longer than without the rock wool, but for only a couple of days longer. How about soaking the pots, putting saucers under them to hold water, and then making sure there's water in them before you leave? You could always request a neighbor or friend to water your plants while you are away. You could move the pots into a protected site while they're gone, too, so the plants don't lose as much water from wind and the sun's heat. Planting them in larger pots would also help.
Another option is to use a dripper irrigation system, where water is directed into the pots through a narrow tubing system connected to your faucet through a garden timer. It can be used either permanently or just as a vacation aid.
