How often should I mist my bonsai tree?

All trees grow in more humid conditions than our homes, offices and dormitories. So what can we do to provide this essential humidity? Misting the tree is only beneficial for a short time so folks in very dry climates may try placing the the tree on top of a shallow humidity tray though there is some recent debate over efficacy.

Misting too often can actually promote rot and is not recommended for bonsai such as jade or portulacaria afra. It may be more beneficial for coniferous bonsai if forest studies are applicable to bonsai (unproven). The consensus appears that for trees recovering from heat stress there may be benefit, but misting on a schedule, just like watering on a schedule, is not necessary, and potentially harmful. Other techniques such as creating a mini-greenhouse temporarily using a bag or adding a humidity tray may work better.

Humidity tray theory and real world results

The theory is that, as the water in the tray evaporates it creates a humid environment around the tree 24 hours a day. The rocks serve to keep the pot elevated out of the water to prevent the soil and roots from staying soggy and provide more surface area for evaporation which creates more humidity around the bonsai tree. The tray is then refilled as the water evaporates.

However, some folks have tested the theory and find it does not make a significant impact. Results would probably be impacted by the size of the room, if indoors, and how much wind or breeze there is. Moisture is going to normalize into a given space and any breeze would move the evaporated water away quickly. This was tested to a degree by Jim Hole. So humidity trays will be more effective when the space is smaller and has less air movement.

Similar results to humidity trays may be accomplished, potentially even more effectively, by clustering more bonsai trees or plants together in the same space. As they transpire they will create a canopy of humidity. In a breezy space this too could have limited effectiveness that may be partially offset by how close together they are with the other plants or trees.

Are humidity trays useful?

Despite the debate over effectiveness humidity trays for generating localized humidity around the bonsai tree. There are less debated applications such as keeping smaller mame or mini bonsai from drying out. In hotter months it can be challenging to keep smaller bonsai from drying out because their pots are smaller and cannot hold as much water.

The humidity tray is filled with sand or very fine rocks and the pots are partially set in it. This acts sort of like a larger pot or reservoir to keep the tree from drying out between waterings. As mentioned, this is great when there is increased water demand by the tree in summer or when you go on vacation.

Last, as they are essentially drip trays, they are undoubtedly effective at protecting tables from water dripping from bonsai pot drain holes.