Aerial Roots and Banyan Trees

In the tropics there are trees that appear to be a grove or small forest of trees and may cover a few acres. On close inspection they are actually a single tree with secondary trunks arising from its branches. This style of tree is called a banyan, and is named after the Asian Indian traders who gathered around and under the trees to conduct their daily business and keep out of the intense sun.

The banyan style is not specific to Ficus but occurs in numerous different types of trees including Ficus, Schefflera, Pandanus, mangrove and other plant families.

Ficus microcarpa with many aerial roots near the main trunk.

Magrove with a curtain of fine aerial roots.

Pandanus with many prop roots.

Even within the Ficus or fig family there are species that form aerial roots and others that never form aerial roots and banyan formations. Aerial roots allow the tree a way to survive on inhospitable terrain such as rocks, and even other trees . Many figs start life on other trees. These are called strangler or epiphytic figs.

A young eppiphytic fig growing on the left side of the palm tree trunk.

The banyan style can be accomplished in bonsai with the appropriate tree materials. Ficus, Schefflera and Brassaia will spontaneously form a banyan type grove. With the figs aerial roots form on mature wood but not on green twigs. Humid conditions and shade promote moisture accumulation on the tree, and this stimulates small whitish-brown bumps and small roots to form on branches and trunk.

Small "bumps" begin to form aerial roots on this fig's trunk.

These tiny roots elongate, grow downwards, and are shaped by wind and other disturbances into pillars, spirals, or many other possible configurations

Aerial root is elongating.

Once the root succeeds in growing into the ground it becomes thicker, stiffer and also shortens a bit.

Aerial root has elongated and rooted into the ground.

Aerial roots, which are not anchored in the ground and fortified with mature bark are susceptible to drying and death. Immature aerial roots are brittle and can break off with careless handling.

Encouraging Aerial Roots

In bonsai culture encouraging aerial roots involves techniques to keep the bark moist, and to maintain high humidity. Lucky growers in the tropics with high humidity and constant warmth have no problems in developing aerial roots. Under northern and indoor growing conditions aerial roots are much more difficult to establish due to the lower humidity levels, and the lack of overhead watering.

Once aerial roots begin to elongate they can be helped by anything that keeps the roots from drying out. Moss carefully draped around the new roots; drinking straws in which the roots have been inserted; bottles of water into which the roots have been directed; plastic baggies around the roots all allow the roots to remain moist and to grow into the ground. Once secured in the ground the roots toughen and then require no special maintenance.

The red lines indicate two drinking straws which enclose aerial roots guiding them to the soil or into a dish of water.

Other Techniques for Developing Aerial Roots

There are a few techniques to successfully place a root exactly where you want it. This involves grafting either a root or seedling tree to the host plant. First, remove some fresh long roots from the fig that you wish to graft. In my case I was repotting a Ficus salicifolia. I removed four long unnecessary roots, and these were used immediately and were not allowed to dry out. The roots were from the same tree but probably roots of the same species would be fine as well. If using roots from another species the bark character may not be similar and therefore the roots will look out of place.

I simply planted several inches of the root end into the pot in the exact spot were it was wanted. The length of the root that was exposed to air should be wrapped in moist sphagnum moss and then covered with plastic to keep the root moist until it successfully roots. Notch the branch on the mother tree and inserted the cut end of the root. Make the notch or hole in the branch slightly smaller than the root's diameter. Then use cut paste around the joint graft, but be careful not to wiggle it apart. For stability, wire the new aerial root joint to the host branch. This protects the joined areas from moving in the wind or from being bumped when watering.

In sixty to 120 days you will find the root has taken as signified by its increasing girth. If the graft fails the root will shrivel up. Once the root has taken the protection wire may be removed and the wrapping moss and plastic can be removed. The successful root will be in the right spot and at the right angle. If the graft does not succeed then get another root and try it again; you have not lost anything but a worthless extra root.

A second but similar grafting technique is to use a small fig tree to graft into the host tree exactly where a new aerial root is required. Notch the host area wide enough to receive the small trunk and allow the grafted tree to grow wildly for 3 - 4 months. After that time the seeding should be fused into the host tree; then the top of the seedling may be cut off allowing the trunk of the seedling and its roots to remain. Again an aerial root was developed exactly where needed.

Styling a Banyan Tree

Styling a banyan is as individual as styling any bonsai, but it is very trying since multiple "trunks" and complex surface root systems are involved. Roots and trunks should be consistent in character and preferably not at random angles. Trunks should be similar in configuration, that is, all upright or all twisted. The branch structure can be anything from formal upright, informal upright or anything else, but the aerial roots must complement the overall pattern.

As with any art piece, if there is "too much" going on there will be confusion and the design may not work. Aerial roots/trunks should be selected for their size position, and shape. The aerials may be wired, replanted at better angles, or removed if not needed. Manipulation of aerial roots should only be done after they become woody and less fragile.