The best way to water a garden is drip irrigation. You do have to manually lay the tubing and then in the fall roll it up. But there are farmers doing it in large fields so a small garden should be possible. Once everything is hooked up it can be pretty well automated. Home Depot now in some stores has drip irrigation supplies.
you don't need anything fancy for drip, a small hole in the pipe and a timer on your pump is is generally enough. If you really want to go fancy you can isolate the system and use moisture sensors, which are cheap.
Moisture sensors that measure conductivity are pretty useless unless frequently recalibrated but time domain reflectometry sensors are much better and more accurate.
https://www.dripworks.com/drip-irrigation