A humidity tray is a simple tool used in houseplant care to help tropical species thrive in drier indoor environments. It consists of a shallow, waterproof container filled with a layer of material like pebbles or gravel, with water added to the base. The tray’s function is to create a small, localized zone of increased moisture directly around the plant’s foliage. This addresses low indoor humidity, which causes problems like browning or crispy leaf tips on humidity-loving plants.
The Science Behind Humidity Trays
The humidity tray functions through the physical process of evaporation. As water in the tray is exposed to the air, it changes state into water vapor. This vapor rises into the air immediately surrounding the plant’s leaves, slightly increasing the relative humidity in that area.
The pebbles or gravel serve a dual purpose. They significantly increase the surface area for evaporation, releasing more moisture than a simple pool of water. The material also acts as a barrier, elevating the plant pot above the waterline and preventing the soil from wicking up standing water. Keeping the pot dry avoids root rot caused by saturated soil.
Setting Up and Maintaining the Tray
Select a waterproof tray slightly wider than the plant’s canopy, allowing space for moisture to rise. The tray should be deep enough to hold material and water, with one to two inches generally sufficient. Fill the tray with a single layer of clean pebbles, gravel, or expanded clay aggregate (LECA).
Pour water into the tray until the level sits just below the top surface of the pebbles. Confirm that the base of the plant pot rests only on the dry pebbles and does not touch the standing water. This elevation prevents the drainage holes from drawing excess moisture into the soil. Maintenance involves routinely checking and refilling the water as it evaporates, often every few days, to ensure a consistent moisture supply. Using distilled or filtered water helps minimize the buildup of mineral deposits on the pebbles.
Factors Influencing Effectiveness
The boost in humidity provided by a tray is highly localized and minimal, typically ranging between five to fifteen percent near the plant. The effectiveness of this change is heavily influenced by the surrounding environment. Warmer room temperatures increase the rate of evaporation, meaning the tray needs more frequent refilling.
Air circulation, such as drafts from windows, heating vents, or fans, rapidly disperses water vapor into the room. This quick dissipation prevents the formation of a stable, humid microclimate around the foliage. Grouping several humidity-loving plants together on a large tray can help, as their collective presence and natural transpiration reduce air movement and trap moisture more effectively.
Other Ways to Raise Local Humidity
When a humidity tray does not provide enough moisture for sensitive tropical plants, other methods can achieve higher humidity levels. The most reliable alternative is an electric humidifier, which releases a fine mist and significantly increases the ambient humidity of an entire room.
Another strategy is to place plants in naturally humid areas of the home, such as kitchens or bathrooms, provided they receive adequate light. Grouping plants closely together allows them to benefit from each other’s transpiration, creating a shared pocket of moisture. For sensitive plants, an enclosed environment like a cloche or terrarium effectively traps moisture and maintains a high humidity level.