Roots In the Air

Roots in the ground — that's how it's supposed to be. Tree trunks are above the ground, holding branches that jut out through the air, and below the trunk, under the ground, are the roots. All the trees you see in this part of the world stick to that plan. Head south from here seven hundred miles or so into south Florida, or go to Brazil or India or the Philippines, and you'll see trees that seem to have a different idea. Banyan trees grow in those places, and banyan trees have aerial roots.

Banyan is a catch-all phrase for several different species of figs (Ficus sp.) that share the trait of producing what are known as prop roots from their trunks and branches. Emerging like threads from the tree's bark, these roots are pulled downwards by gravity until they come in contact with the ground. Over time the prop roots become more stout and are covered in the same bark as found on the tree's trunk and branches. With their increased size the prop roots become auxiliary trunks, "propping up" extending limbs, allowing the parent tree to spread itself ever outward. The sprawling nature of banyan trees sometimes poses problems for people, but there's no denying the strangely fascinating appearance of the aerial roots.

A banyan growing outside the courthouse in Fort Myers, Florida *Attribution: Wknight94* *Wikimedia Commons*

A large banyan with a branch extending over a road, the aerial roots trimmed to create a passageway *Attribution: TR Shankar Raman* *Wikimedia Commons*

The relentless expansion of banyan aerial roots swallow everything in their path *Attribution:* *Wikimedia Commons*

There are several bonsai in the Arboretum collection with the capacity to produce aerial roots, but on only two specimens have we permitted them to develop. The look of those spaghetti-like appendages dripping down in a tangle from trunk and limb commands attention. Aerial roots also take management and require space and time to develop, so despite their appealing novelty it is not always desirable to let them go about their business. It is easy enough to rub off the roots when they are first emerging as little threads, same as you might rub off unwanted leaf buds before they break into growth. Banyans have their reasons for producing aerial roots, yet in container culture they can also survive just fine without them.

The two bonsai specimens in our collection that feature substantial aerial root development are a Chinese banyan (Ficus microcarpa) and a cultivated form of benjamina fig (Ficus benjamina 'Exotica'). What follows are the histories of each.

Chinese banyan: This specimen came to the Arboretum as part of the Staples' donation in 1992. Here is what it looked like in early 1993:

There is no way of knowing when looking at the above photograph, but the banyan was small enough then to be held in a single hand. No one at the Arboretum knew tropical species very well so we had to do some research to learn the tree we had was a Chinese banyan. The botanical name we found for it then was Ficus retusa, although that appellation is apparently no longer thought to be correct. Whatever name it might be called, this specimen right away revealed itself as a vigorous grower, and from early on exhibited the tendency to produce aerial roots. There are a few young aerial roots visible in the first image, plastered to the tree's trunk. These were subsequently removed, only to be quickly replaced with new ones. By the time of the next image, made two years later, it can be seen that two aerial roots had been allowed to reach the soil surface and establish:

The next four images of this specimen cover a period of six years. While examining the pictures, take note of how the tree gradually takes shape through development of its branching. Also note the progress of the aerial roots, which start out like threads and gradually attain size and substance:

The vigor and extended growing season enjoyed by tropical plants makes them develop faster as bonsai subjects than their temperate counterparts. The Arboretum's greenhouse allows for virtually year-round growth, although there is still some seasonal ebb and flow. The degree to which our Chinese banyan has over the years continually added branching and attained mass in its trunk has been truly impressive. Keeping up with its robust growth habit can be challenging, especially during the months when all of the collection is in active growth.

No pictures were made of this specimen for the next six years, until it turns up again in 2010 out on display in the bonsai garden:

The following year the Chinese banyan was photographed again, this time after being transplanted into a new container:

Observant readers will note that every picture of this specimen shown so far has presented the tree in a different pot. Sometimes it takes a while for the right container to come along.

This picture from 2018 shows the Chinese banyan in yet another pot, one in which it has ever since remained, made by Dale Cochoy of Wild Things Bonsai:

The branching and general structure of the tree as seen above reflects a strong naturalistic identity. The personality of the tree is coming to life with a sense of sinuous movement, its contorted branches reaching in every direction for light.

In 2019 this specimen was the logo tree for the final Carolina Bonsai Expo:

In addition to the ever-increasing superstructure of aerial roots, a point of design interest on the Chinese banyan is the way the first branch on the left side of the tree developed over time. Prior to the 2004 image the branch is simply extending laterally as any lower side branch might, but in the 2010 image that same branch makes a sharp ninety degree upward turn. For the next decade it continued in ascending fashion until the branch was behaving like a little tree of its own. The limb was allowed to grow like that because there was empty space above it. There was no need for the branch to keep reaching outward when it had room to grow upward, and this reflects an observable truth about how most trees in nature behave. The little banyan wanted to behave that way, too, so it was allowed to for the sake of creating visual interest.

Creating interest is all well and good, but things eventually run their course. After several years the upward growing branch became disagreeably stout and started bumping into the branching above it. As the suggested storyline for this specimen goes, a storm blew through and ripped off a couple parts of the upward growing branch, lowering its profile and thinning it out. In reality, it was a design decision made to alleviate a congested area in the tree's crown:

The Chinese banyan is currently on display at the Baker Exhibit Center greenhouse, and it looks like this:

Exotic Fig - This specimen was donated to the Arboretum in early 1995 by a man named Tom Stout. He lived way up in a shady holler surrounded by the Cherokee National Forest in eastern Tennessee, a most unlikely place to grow tropical bonsai. Tom had started the tree from a cutting and trained it to grow over a piece of coral. He had the tree in effect clasping the coral and both were situated on a limestone slab, making for an unusual presentation. The tree was still in development and the fact that it was a different take on the “root over rock” form is what made it a worthwhile addition to the Arboretum’s young collection. The exotic fig took its place with the other tropical bonsai in the greenhouse, but was viewed as a work in progress, a project that would take some time to mature. As an unfortunate result, no photos were made of this specimen for the first nine years we had it.

The first image of the exotic fig on the piece of coral was made in 2004. By that time the arrangement had been transplanted from the limestone slab to a stoneware tray:

As can be seen in the above image, the roots that clasped the fig to the chunk of coral were aerial roots. Tom had taken the aerial roots when they were just young, flexible strands and threaded them through holes in the coral. Several other more substantial aerial roots had been draped around the coral like arms. When we received the donation this creative root work was still relatively new, and looked it. By the time of the photograph those first aerial roots had matured and become substantial, even to the point of sending out more aerial roots of their own. The combination of aerial root and coral was really the best part of this specimen. The structure of the canopy was stiff and not nearly as interesting as what was going on beneath it.

In an effort to make the entire presentation more effective, the upper half of the tree — everything above the first branch on the left side of the tree as seen in the photo — was removed. The intention was to build a new and better crown. The years it would take to achieve this goal would also result in further maturation and improvement of the base of the tree, the part with the aerial roots entwined with the coral. While all this was taking place the exotic fig once again receded from notice and no photographs were made of the process.

Exotic figs are a cultivated variety of the benjamina fig, and benjamina figs that are happy with their environment grow like weeds. It did not take all that long for the cut back fig to produce all the necessary parts to build a new crown. The next available images show the exotic fig being worked on in a demonstration program for the Bonsai Society of the Carolinas in Charlotte, North Carolina, in 2014:

2014 - Hacking back rampant growth with hedge cutting shears

By the end of the demonstration a new trunk line and branching structure were established

Here is a portrait showing the new form of the exotic fig as it looked two years after the demonstration:

The following images, made at the same time as the image above, show the specimen from two other perspectives:

The exotic fig with aerial roots over a piece of coral finally made it out on display in the bonsai garden, as seen in the next two photos:

The images above were made two years apart. Take notice of how new aerial roots continue to be produced, as can be seen in the second photo.

In 2021 the exotic fig was planted in an American bonsai container made by Eli Akins of Waldo Street Pottery. Here is a recent photo, showing the specimen on display in the Baker Exhibition Center greenhouse:

Addendum: Aerial roots take several different forms in a variety of plants. A native species that produces a type of aerial root for propagative purposes is the wild strawberry (Fragaria virginiana), with the roots in question referred to as stolons. Mistletoe (Viscum album), a parasitic plant, produces roots that start out in the air but adhering to the bark of a host tree before burrowing into the host’s tissue. These are referred to as haustorial roots. The strange knees produced by baldcypress (Taxodium distichum) growing in very wet conditions are also considered aerial roots, termed pneumatophores, and are thought to aid in gas exchange. The exact purpose of cypress knees is uncertain, but they are appendages that grow off of roots in the ground and project upwards into the air, producing no chlorophyllic material.

tree story 2Journal EntryFebruary 28, 2025year 3, winter 2025Comment