Humidity is the measure of water vapor present in the air, known scientifically as relative humidity. Many popular houseplants, particularly those from tropical rainforests, thrive in environments where atmospheric moisture is consistently high. When these plants are moved indoors, central heating and air conditioning often reduce the humidity far below their native levels. This dry indoor air causes plants to lose water through their leaves faster than their roots can absorb it, a process called transpiration. Addressing this moisture deficit is important for maintaining plant health.
Identifying Signs of Low Humidity
Plants suffering from insufficient air moisture exhibit several noticeable physical symptoms. The most common sign is the browning and crisping of leaf edges or tips. This damage occurs because the plant is rapidly losing water and cannot keep the delicate leaf margins hydrated under dry conditions.
Another indicator is the development of yellowing leaves or the dropping of flower buds before they open. New leaves may also emerge smaller than normal or fail to unfurl completely, leading to stunted growth. To accurately assess the environment, a hygrometer is used to measure the relative humidity percentage in the room.
Most tropical houseplants prefer relative humidity levels between 40% and 60% for optimum health, though some species thrive closer to 70%. In contrast, the average home, especially during winter, can fall below 30%. Monitoring this measurement allows plant owners to determine if intervention is required to reach the desired range.
Simple Methods for Increasing Ambient Moisture
One accessible, low-cost technique involves using a pebble tray placed beneath the plant container. This method utilizes evaporation to create a localized zone of higher humidity around the foliage. To set up the tray, a layer of pebbles is placed in a shallow saucer, and water is added until it rests just below the top of the pebbles.
It is important that the bottom of the plant pot does not sit directly in the water, which can lead to root rot. As the water evaporates from the tray’s surface, the moisture content immediately surrounding the plant increases. This technique is most effective for smaller plants or when the tray extends beyond the width of the plant’s canopy.
Clustering plants together is another effective strategy that relies on the natural process of transpiration. Plants continuously release water vapor through microscopic pores in their leaves, and grouping them creates a shared microclimate. When several plants are placed in close proximity, the collective moisture released becomes trapped, raising the local humidity level.
Misting the leaves with a spray bottle is often suggested, but its effects are short-lived, dissipating within minutes. While a quick mist can briefly hydrate the leaf surface, relying on it for long-term humidity control is ineffective. Persistent water droplets on leaves, especially in areas with poor air circulation, can increase the risk of fungal and bacterial diseases. If misting is used, it should be done lightly in the morning to allow the foliage to dry completely before nightfall.
Technological Solutions and Enclosures
For more significant or consistent humidity control, mechanical devices like humidifiers are the most reliable option. Humidifiers work by releasing a fine mist of water vapor directly into the air, effectively raising the room’s overall relative humidity. Cool mist humidifiers (ultrasonic and evaporative types) are preferred for safety since they do not involve boiling water. Warm mist units create steam, use more energy, and pose a minor burn risk. The device should be placed near the plants but not so close that the foliage is constantly wet, which invites disease. Consistent cleaning of the humidifier reservoir is necessary to prevent the buildup and dispersal of mold or bacteria.
Creating a sealed or semi-sealed environment is an excellent way to maintain high moisture levels for plants that demand 70% humidity or more. Terrariums, glass cabinets, or miniature greenhouses function as closed systems that recycle the moisture released by the plants and the soil. The enclosed nature of these structures minimizes moisture loss to the surrounding room, making them ideal for ferns, mosses, and certain orchids.
A simpler, non-mechanical solution is to place plants in naturally humid areas of the home, such as a kitchen or bathroom. These rooms typically have higher ambient moisture from running water and steam. This approach is only viable if the chosen location also meets the specific light requirements of the plant.