I’m not very confident in using a chopstick to detect bonsai soil moisture level in a bonsai pot because the chopstick has to be completely removed to check for dampness. Also, the porosity of the wood it is made from varies which affects the degree of moisture absorption and retention. So, I’ve been experimenting using clear plastic tubing as an indicator of soil moisture presence or absence. I am using pieces of narrow, flexible plastic medical grade tubing that is made for patient oxygen delivery.
Place a stiff wire through a short piece of tubing and fold the wire over at each end to hold the wire inside of the tubing. Shape it like a candy cane. Make a hole in the soil with a chopstick and place the long end of the moisture probe into the hole at the desired monitoring depth. Retract the moisture probe just a bit to make sure the end of the tube is not obstructed with soil particles.
The water vapor in the soil passing through the tube condenses on the inside of the tube, visibly indicating the presence of soil moisture at the probe’s depth and location in the pot. The moisture probe is U-shaped so the end of the tube above the soil will not take in water from above. If there is no visible condensation in the tube above the soil’s surface slightly lift the probe out to see if condensation exists in the tube below the soil’s surface.
The preliminary results are encouraging. Give it a try and let me know if it works for you.