I think Pryv may meet most of your requirements.
Log what you want
You can log data (numeric or not) and see numeric as graphs. I also used as a diary for one time.
Share what you want
You can choose to share some of your Pryv data (let's say your tomatoes harvest) with other users via a URL while keeping other streams private.
If you are an IFTTT, you can integrate it with Pryv and have data automatically recorded (I copy my FitBit weight and tweeted quotes automatically to Pryv).
What might be missing
I do not know about a CSV export either, but this would probably be complicated due to the wide range of data you can log in Pryv.
Possible drawback (to be checked)
Please note I never experimented with the iPhone application. I know only the web version and I am not sure you can keep your data only on your phone. I suppose the app is just another client for the web version.