Indoor air, especially during colder months or in climate-controlled environments, often lacks the moisture that many popular houseplants crave. Tropical plants originate from environments with naturally high humidity and show signs of stress, such as crispy leaf edges or browning tips, when the air is too dry. A humidity tray offers a straightforward, low-cost solution to slightly increase the immediate air moisture around a plant without requiring an electric device. This technique uses the natural process of evaporation to create a more favorable microclimate for moisture-loving foliage.
Defining the Humidity Tray
A humidity tray is a non-mechanical setup designed to manage air moisture around a potted plant. It consists of three primary components: a waterproof tray, a layer of non-porous medium, and water. The tray can be a standard plastic plant saucer or any shallow, watertight dish that is wider than the plant’s pot.
The medium, typically small pebbles, gravel, or lava rock, is spread evenly across the tray’s base. Water is then added to the tray, reaching a level just below the top surface of the pebbles. The pebbles elevate the plant pot above the standing water, preventing the pot’s drainage holes from sitting in moisture. This elevation is critical to avoid waterlogging the soil, which can quickly lead to root rot through capillary action.
The Science of Localized Humidity
The tray’s operation relies on the physical principle of evaporation, where liquid water turns into water vapor and is released into the surrounding air. As the water in the tray converts to vapor, it raises the relative humidity (RH) directly above the tray and around the plant’s leaves. This effect is highly localized, creating a small, moist “microclimate” that mimics the plant’s native humid habitat.
The pebbles increase the surface area from which evaporation can occur. Water wicks up between the individual stones, exposing more water surface to the air than if it were just a flat dish of water, thereby increasing the rate of vaporization. While a humidity tray does not significantly alter the humidity of an entire room, it can create an increase of roughly 3 to 10 percent RH directly at leaf level. This small, consistent boost can be enough to reduce the stress and visible damage on thin-leaved tropical plants.
Setting Up and Maintaining Your Tray
Setup
Select a water-tight tray that extends at least a few inches beyond the diameter of the plant’s foliage. Fill the tray with a layer of clean, non-porous material, such as smooth river stones or coarse gravel. The material should be deep enough to provide a stable platform for the plant pot. Pour water into the tray until the level is just below the surface of the stones, ensuring no water is touching the base of the plant pot. Placing the tray near a bright window or another warm area will encourage faster evaporation, thus maximizing the local humidity effect. The warmth from the light or surrounding air increases the energy available for the water to change state.
Maintenance
Check the water level daily and refill the tray as needed. Periodically, about once a month, the tray and pebbles should be emptied, scrubbed, and rinsed. This removes mineral scale and prevents the growth of algae or mold. Using distilled water or rainwater instead of hard tap water minimizes the buildup of mineral deposits on the stones over time.
Other Ways to Increase Plant Humidity
Grouping several humidity-loving plants closely together is an effective strategy. This method capitalizes on the collective transpiration from all the plants, pooling the moisture they naturally release into the air and creating a shared humid zone.
An electric humidifier remains the most reliable and effective way to achieve a substantial increase in whole-room relative humidity. These devices can consistently maintain the 50 to 70 percent RH preferred by many tropical varieties. Misting the plant’s foliage with a spray bottle offers only a temporary increase in moisture, as the fine water droplets evaporate quickly, often providing more immediate benefit to the caretaker than to the plant itself.