YOu might want to consider a big tonic bottle with the cover attached and a small hole punched into the cap. Fill with water and push into the soil. Maybe a neighbor can water while your away.

If these are outside, run a soaker hose and attach a timer to it. That's what I've got, it goes off twice a day for an hour each and keeps everything beautifully hydrated. It's also a much more efficient way of watering since it is slow and can seep in deep.