A humidity tray is a tray filled with water and pebbles or charcoal that sits under a bonsai tree. It helps to create a humid environment around the tree and prevent the roots from drying out. A humidity tray is especially useful for bonsai trees that need high humidity, such as tropical and subtropical species.
To use a humidity tray for bonsai, you need to find a tray that is large enough to fit your bonsai pot and fill it with pebbles or charcoal. The pebbles or charcoal should be about 0.5 to 1 inch high and cover the entire surface of the tray. Then, place your bonsai pot on top of the pebbles or charcoal, making sure that the bottom of the pot does not touch the water. Water your bonsai tree from above, letting the excess water drain into the tray. The water in the tray will evaporate slowly, increasing the humidity around the tree.
You should check the water level in the tray regularly and refill it as needed. You should also clean the tray and replace the pebbles or charcoal periodically to prevent algae and mold growth. A humidity tray can help your bonsai tree thrive in dry conditions and improve its health and appearance.