Fair enough. 
In that case, any of the various irrigation systems should work for your project. The simplest is just a dumb but electric water valve connected to a Smart plug (or in your case a relay) and then you turn the power on when you want water.
Check the quick browse lists for “pet and livestock projects“ and for irrigation and you should get lots of ideas. Many of them will be out of date as far as the automations side since they will reference smart apps or groovy, but for your purposes, that’s easy enough to replace with schedules in the current architecture. And the hardware ideas should all still be relevant.
FAQ: Using the quick browse lists without the community wiki
Or if you just want to go straight to looking at relays, the Zooz models are popular. These are Z wave so the range is good, they work well with SmartThings and the manufacturer provides their own custom edge drivers, their tech-support is very good, safety certifications are good on most models, they are well engineered, and the price is good.
This is the house brand for the retailer The Smartest House. Also available on Amazon if you prefer that.
There are also fully automated zwave water valve shutoffs That work with SmartThings, but they are way more expensive and The dumb but electric valve controllers sound like they will work just as well for your use case. 