Hmmm if its a greenhouse you may want to spend a little more and get a "ruggedised" Arduino.
They cost a little more but somebody did a gardening project where the Arduinos were getting trashed by lightening spikes and these seemingly solved the issue. Of course there are other ways to make them more robust.
Another thing to consider is the length of wires and type of wire from an Arduino to any sensors.
This should always be as short as possible and if not possible then using properly SHIELDED cable.
Power supplies are also a key factor in these types of environment too.
But for an on the bench test setup pretty much any Arduino will do the job.
My preference would be a UNO with maybe a relay shield to simplify it all.