Well, that tree looks great! It's a beautiful healthy one you started with so thinkig you will have good success with it during the summer. I don't trust those meters, so I use a wooden dowel for those bigger ots and push it right into the root zone and below. If it comes out moist by touching that dowel to your face, it's not time to water yet.
That mix you used holds a lot more moisture than I would care to use for my gardenias. I also hate growing them in plastic, unless they were in a mix that dried our very fast.
For my trees, I like to be able able to water again in less than a week in summer, and less than that during the winter.
Keep a close eye on it and if you really want to make sure if it's time to water, feel the weight of that pot, since plastic is easy to read, or use a wooden dowel in a deep pot like that.
Did you bury the roots deep into that pot? Are they occupying the bottom 2/3? If not the bootom will stay more moist than the top portion until the roots grow down deeper. Don't be fooled thinking your trees does not need watering when the root portion is dry. Rains won't hurt and in fact help. You should not have to pull it out from the rains in the summer if you are using a good mix)
If you really care about that tree and want to be successful through the winter too, you need this arsenal at all times.
A good fertilizer one that contains Ca, an acidic one or make your own acidic solution using vinegar, and a good horticultural spray for pests.
Q