This is the Moisture meter that I use, works just fine for me. Very inexpensive and can be purchased just about anywhere. I wait until the needle is just beginning to touch "RED" dry markings then water as needed.
Thanks so much for the info Oldschool 64, will have to try this I think may benefit both my wife and I. We both have arthritis pretty bad and I'm going to have knee replacement surgery sometime in May, hopefully this will help with the day to day pain and the surgery. I have an unknown plant...