My pencil plant has a couple of yellow stems. What is the problem?
The following article addresses Euphorbia truncalli (Pencil Cactus): https://www.gardeningknowhow.com/ornamental/cacti-succulents/pencil-cactus/care-pencil-cactus.htm
Yellowing stems can mean several things; age, injury, temperature and too much/little moisture. Sometimes my "pencils' throw off old segments for seemingly no reason. It's kind of like when we lose a hair or two! If the plant has recieved a physical (or mechanical) injury, the connection between stem joints could have been broken. Euphorbia's are notorious for throwing leaves and segments when traumatized by temperatures too low or drought. The plant is trying to conserve it's resources by "downsizing". And, this plant is a succulent, don't keep it wet. Let it dry slightly between waterings.