Aerial Root Management and Uses in Houseplants｜Growing Techniques for Aerial-Root Plants Such as Philodendron and Monstera

Among houseplants, there are species that produce aerial roots, such as philodendrons and monsteras. Aerial roots are an important organ that expresses both the growth and the beauty of a plant. However, many people do not understand what aerial roots really are, regard them as "roots that get in the way," and tear them off. This is a major mistake that hinders the plant's growth. By understanding aerial roots and managing and utilizing them appropriately, you can accelerate the growth of houseplants and further enhance their aesthetic value. This guide explains in detail the biological role of aerial roots, practical management techniques, and even aesthetic expression that makes use of aerial roots.

What Aerial Roots Are: A Product of Root Function and Evolution

Aerial roots are roots that emerge from the stem into the air. Ordinary roots absorb water and nutrients within the soil, but aerial roots are specialized roots that absorb moisture from the air. Aerial roots appear in abundance on trees in high-humidity environments such as tropical rainforests, where roots have difficulty reaching the ground. Philodendrons and monsteras are epiphytes that cling to tropical rainforest trees and grow using their bark. Because they live far from the ground, they developed aerial roots and evolved a strategy of absorbing moisture from the humidity in the air. The moisture absorbed through the aerial roots is supplied throughout the plant and becomes energy for growth. In other words, cutting off aerial roots is equivalent to depriving the plant of a pathway for taking in nutrition. By creating an environment where aerial roots function soundly, you can accelerate the plant's growth rate by 1.5 to 2 times.

The Mechanism of Aerial Root Formation: Humidity and Light Are Key

Specific environmental conditions are required for aerial roots to form. When aerial roots do not appear, the cause is usually inadequate environmental conditions. The most important factor in aerial root formation is humidity. In dry environments where the relative humidity of the air is 60% or below, aerial roots hardly ever form. For aerial roots to appear, humidity of at least 65 to 70% is necessary. The reason aerial roots are unlikely to form when philodendrons and monsteras are left sitting by a window is that indoor humidity in winter drops to around 30 to 40%. The next most important factor is temperature. The optimal temperature for aerial root formation is 20 to 28°C. Within this temperature range, aerial roots form actively and grow quickly. Below 15°C, aerial root formation almost completely stops. And light is important as well. Aerial roots extend in the direction from which light comes. Plants placed in dark environments are unlikely to produce aerial roots, and any that do form will be weak.

Building a Growing Environment That Makes Use of Aerial Roots

To make the most of aerial roots, you need to deliberately create an environment where the plant can absorb moisture from the air. The most effective method is the use of a moss pole (or moss support). A moss pole is a cylindrical support made from coconut palm bark fiber. If you regularly mist the moss pole with water, the moss pole stays constantly moist. For species that readily produce aerial roots, such as Philodendron pinnatum, having the aerial roots wrap around the moss pole allows the plant to absorb moisture directly from the stem through the moist moss pole. To install the moss pole, stand it beside the plant and position it so that the stem can make contact with the moss pole. Wait 2 to 4 weeks for the aerial roots to wrap around it naturally. Once the aerial roots have attached to the moss pole, mist the moss pole daily to keep it moist. Continuing this routine dramatically accelerates the plant's growth rate.

The next most important method is humidification. Place a humidifier around the houseplant, or place a damp cloth around the plant, to keep the humidity of the air constantly elevated. When humidity is maintained at 70% or above, aerial roots begin to appear one after another. In the case of large species such as Monstera deliciosa, humidification has been reported to increase the size of new leaves by 20 to 30%. And ventilation is important too. Even if you raise humidity through humidification, disease becomes more likely to occur without ventilation. By using a fan to maintain constant gentle air circulation, you can achieve a high-humidity environment while minimizing the risk of disease.

Turning Aerial Roots into Auxiliary Roots: Burying Them in the Pot

Another way to make further use of aerial roots is to bury them in the soil and turn them into auxiliary roots (aeration roots). This method can be applied to species that produce many aerial roots, such as Philodendron pinnatum and Philodendron bipinnatifidum. Once the aerial roots have grown to a sufficient length (5 cm or more), either move the plant to a lower position or raise the pot to a higher position so that the roots touch the soil in the pot. When aerial roots come into contact with soil, root hairs automatically develop and they begin absorbing water and nutrients from the soil. Through this conversion into auxiliary roots, the plant's water and nutrient absorption increases and the rate at which new leaves unfurl accelerates.

Using Aerial Roots as Aesthetic Expression

Aerial roots have aesthetic value as well as biological function. By deliberately making use of aerial roots, you can enhance the decorative value of houseplants. For example, letting the aerial roots of a Monstera deliciosa hang down from a hanging pot creates a natural, waterfall-like appearance. By wrapping the aerial roots of a heartleaf philodendron around a moss pole and training them into a spiral, you can create a unique three-dimensional form. Furthermore, by immersing aerial roots in the water of a hydroponic setup, it is also possible to achieve a completely transparent appearance.

Management to Keep Aerial Roots Healthy

Regular observation is important for maintaining the health of aerial roots. Healthy aerial roots range from light brown to a somewhat pale color and feel springy to the touch. If an aerial root turns black or becomes mushy, it is a sign that rot caused by pathogenic bacteria has begun. In this case, remove the affected aerial root and apply a fungicide. However, you should avoid cutting off all of the aerial roots. Carefully cut away only the rotted portion and preserve the remaining healthy aerial roots. In addition, when a great many aerial roots have formed, it is also useful to periodically prune the older aerial roots while taking the plant's weight balance into account.