Using a timer switch for power, how to wire two lights so that when one is on the other is off
You could use a smart plug like a Shelly Plug which will allow you to set up time with built-in tools to automatically turn on and off at dawn and dusk and be controllable with a smart phone. The advantage is that the Shelly is smart enough to automatically adjust to changing daylight hours, which a wall timer will not usually do.
It's hard to argue with the simplicity of a simple timer that @Tim suggests comments for your question.
Edit
There are timers which will allow you to control two different devices from the same power outlet. An example would be the NearPow Outlet Timer, which allows two different devices to have nine on/off settings per day and seven day programmable.
Good luck with the plants.