I connected a SparkFun moisture sensor to a TinyPico.

Basic Analog Read function and some scaling produces a reading from 0-100%.
This is then transmitted using the TinyPico's Bluetooth Low Energy to my Phone.

Using Xcode, I wrote a very basic app to read the BLE Characteristic and display it.
I intentionally added a large delay in the readout to make it readable.

The UI was drawn in Photoshop.
Finally, I drew up a quick case design in solid-works and printed it out.
Job Done!

I do not plan on publishing the App as this was just an afternoon project. However If people are interested I can publish the Code (both Arduino and Xcode).