The large advantage to a greenhouse is being able to consistently control the environment in which the plants reside.
Plants outside are subject to too much or too little rain, too cold or too hot temperatures, etc.
In a greenhouse you have a greater degree of control over environmental conditions. You can control hydration, you can control temperature (to some extent), etc.
The main benefit is that this enables to you to grow plants during seasons where the plants would not be able to survive outdoors, as well as insure against natural fluctuations in expected environmental conditions.
TL;DR its not necessarily more efficient as it is more convenient.
Oldirtybastard58346 t1_jeb530p wrote
Reply to ELI5: Why do people grow plants in greenhouse ? Is it more efficient than growing plants outside ? by dellive
The large advantage to a greenhouse is being able to consistently control the environment in which the plants reside.
Plants outside are subject to too much or too little rain, too cold or too hot temperatures, etc.
In a greenhouse you have a greater degree of control over environmental conditions. You can control hydration, you can control temperature (to some extent), etc.
The main benefit is that this enables to you to grow plants during seasons where the plants would not be able to survive outdoors, as well as insure against natural fluctuations in expected environmental conditions.
TL;DR its not necessarily more efficient as it is more convenient.