August 13, 2021

Crazy for Catalpa! Bonsai prospects for an unusual North American native

         If you're familiar with the northern catalpa, Catalpa speciosa, then you know it's a pretty strange tree and certainly not one which you would expect to be used for bonsai. Maybe it's a fool's errand for me to attempt to tame a tree with 12" leaves and 20" seed pods, however something about that staccato, memorable name has got me captivated. I've been observing specimen of it everywhere I go around Columbus as it is one of the more easily identifiable naive trees around - so much so, I've even got my girlfriend shouting "Catalpa!" every time we pass one. From this foundation, basic identification skills had led me to observe the species more intimately. As with any unknown species, the more scenarios you observe a specimen, the more you can observe its potential for bonsai. In the case of the catalpa, observations of a full-sized specimen, the seeding frequency of seeded, the fast growth of those volunteers, and the discovery of one naturally stunted catalpa all inform my plans to experiment with this species for bonsai.

 Sections

Catalpa is capable of producing a variety of leaf sizes. The left-most leaf is typical for a healthy catalpa, while the right leaves are from a naturally stunted catalpa.


Here is a middle-aged catalpa showing only a fraction of its potential size.


I. Catalpa Characteristics (General)

            Catalpa speciosa goes by many common names, but it has unmistakable characteristics wherever you live. Catalpa are broadleaf deciduous trees that can grow to immense size as landscape trees. The primary characteristics for identification (see pictures below) are their large heart-shaped leaves, white flowers which appear in late spring, and large seed pods which ripen and begin dropping seeds towards the end of summer. The unripe seed pods reminded me of green beans, however, as they ripen, they turn brown and crack open. Once opened, thousands of white seeds can fall out and disperse from a single tree. In addition, bark appears gray-brown with light brown spots on the young specimen or young branches and it matures into a fissured and flakey bark with a light-dark color.

            Although thought to be native to Illinois and Indiana along the Mississippi and Ohio rivers, over the past 200 years, Catalpa speciosa has spread throughout the US northern and western US partially through ornamental and cultivated purposes and partially through natural colonization. Consider this flexible plant hardy anywhere in the US, zones 4-8 (Source).

            Other common names for Catalpa speciosa include the western catalpa (due to recent expansion of its native range west of the Rockies), hardy catalpa, cigar tree (due to the long brown seedpods), and bait or caterpillar tree (due to the catalpa moth caterpillar, Ceratomia catalpae, whose larvae is collected on this tree by fisherman).

The prominent white and purple flowers support numerous pollinators including bees, flies, and hummingbirds. Source.

Here you can see the flower clusters from a more zoomed-out perspective. Source.

The first crop of catalpa seeds - the only ones in reach on the pictured tree.

Luckily each pod has a bounty of seeds for us! This should be plenty for my purposes, and I'll even have extra if anyone is crazy enough to join me in using this species.

Mature bark and flowers. Source.
In this young catalpa clump growing in an unused patch of broken sidewalk, you can see the immature bark.

II. Catalpa Assessment for Bonsai


A. Catalpa seeds prolifically and grows quickly


        I have already emphasized the frequency with which I see this species volunteered in yards, alleys, and along sidewalks of Columbus, but what we have not yet discussed is the speed at which catalpa can grow. These seedlings take off in even the most adverse urban conditions wherever they can find a bit of soil and light. Once established, the large leaf phenotype becomes apparent from a young age, enabling them to grow at a pace of 1-2 feet per year and rapidly thicken their trunks (all those sugars have got to go somewhere!). In open growing environments, this can translate to trees developing 1-inch diameter trunks in the first 2-3 years!

Here is one sample Catalpa volunteer. ~3 feet tall. On the right of Buck is a 1 foot tall, 1st year seedling as well.

You can see by years 2-3, catalpa seedlings already have leaves the same size as their mature parents.

B. Catalpas can dramatically reduce leaf size... in the right condition!


            I promised a natural catalpa bonsai and here it is in all her glory! This is a perfect example of an un-collectible "yamadori" or "urbandori" - if a tree coming out of a tiny hole in cement stairs can be parallel to a mighty mountain tree stuck atop a granite crack. At any rate, this tree is probably at least 2-3 years old given that the trunk thickness is much better than the 1-year-old seedlings I've seen. In the first picture below, you can see it is already starting to develop a hint of taper! In addition, the lowest leaves and branches are very small - some as small as my thumb and some even smaller, although it remains to be seen what those tiny leaves will do in the rest of the growing season or whether these are new leaves. That said - by feel and appearance - they seem to already be hardened off with a waxy cuticle. In the second picture below, these leaves to the leaf from a full-sized catalpa tree. Although the leaves get larger on the top of this crack catalpa, in total this tree is still less than the height of the full-sized leaf, and the largest leaf on this stunted catalpa is still 1/3-1/2 the size of the un-stunted leaf and the average leaf on the stunted tree is even smaller. Some component of the small tree's condition has dramatically changed its phenotype, whether from having confined root-space or limited water or nutrient access due to the awkward growing position. These situations could certainly be emulated and tested in a bonsai pot to try to duplicate this stunted version of the giant tree.

Crack-grown catalpa with minuscule lower leaves and a hint of trunk taper.

Here you can see this crack-grown catalpa is less than the height of one full-sized leaf from a full-sized catalpa.

Another view of the lower leaves and shoots.

C. Catalpas respond to pruning with reliable backbudding

            My next favorable observation for using catalpa as bonsai stems again from the stunted tree. It had a dead top - from what, I'm not sure - but in response to this dead top, numerous young shoots emerged down below which are all healthy and on their way to becoming hardened off branches. This is a promising and basic characteristic to observe when looking into any new species for bonsai because a species that does not backbud well can only rely on more technically difficult/inconvenient methods to rebuild branches such as grafting.

I counted at least 5 lower branches which activated into growing in response to the death of the top. That should be plenty to choose from for bonsai growers!

D. Catalpa deadwood is durable

            This is not a characteristic I have tested for myself yet, however, from my reading, I found that historically catalpa's wood was useful for fence posts and railroad ties due to its natural resistance to rot. This led to many farmers in the Ohio area planting it and it could also lead to durable carving for bonsai artists.

A 120-year-old catalpa from Lincoln, MA shows unique twists, callouses, and deadwood scars. (Source)

III. Potential Disadvantages of Catalpa as Bonsai

            Even if catalpa can be used for bonsai, every species has its advantages and disadvantages. It is too early to definitively state these without testing this species' behavior in a bonsai pot over many years of repeated work, but two issues I'm apprehensive of at the moment are as follows.

A. Brittle branches

            My reading into this species also informed me that it commonly has branches that break during wind, snow, and ice storms. This is of major concern to homeowners who plant these trees nearby, however, it is an even bigger concern to bonsai artists who want to style their trees via wiring! We will have to wire early, or wire very cautiously and gently...

A catalpa with a freshly broken branch in early winter.

B. Possible poor ramification

            Another potential disadvantage of this species as bonsai is that ramification of full-sized trees does not support the idea that a bonsai of it could be as dense as our typical Japanese maple. It remains to be seen when the full-force of bonsai miniaturization techniques are implemented what the effect on branch density and ramification will be, however, worst case scenario we can enjoy them without such density as we do for magnolias and other species with redeeming qualities that outweigh those that we cannot control.

A typical branch from a mature catalpa. Admittedly some of the leaf attachment points (and therefore buds) are quite close together on the lower branch. This leaves me optimistic about activating branch/leaf density and ramification.

IV. Closing thoughts

            It's now been 4 years since I last shared an analysis of a new species which I have observed, (last time, the Antelope Bitterbrush). Much has changed in my life and bonsai experience since then, but my love and curiosity for nature have been unchanged. The habit of observing the plants around me combined with applying that information in bonsai has since given me more of an established framework for analyzing new species when I travel. In this case, I already know catalpa will be a challenge to make into a convincing bonsai, but so far it has enough redeeming qualities to be an interesting subject to attempt. Not to mention the ease of finding this species locally will provide plenty of practice material both for growing from seed/young volunteers and for larger, neglected volunteers which will have a head-start on trunk development. I'll report back on my success with this species in a few years' time. I may find out that they are a waste of time for bonsai! But the scientist in me (or maybe the subconscious ouija board within me) has a good feeling about experimenting on this one. Not every new species will share the same traits of the Japanese species that bonsai artists around the world use so extensively, however, I found from my time at Elandan Gardens that discovering what there is to love in our native trees puts us more in tune with the plants and ecosystems around us. Even if I'm the only bonsai artist who ends up growing catalpa, you can never know for sure when having such silly open-mindedness in bonsai could pay off without running the experiment.

V. Blog Announcements

  1. My old email newsletter subscription service has been retired, so I have migrated to follow.it. This will allow my sporadic new posts on projects relating to the PSBA and CBS bonsai clubs, my own bonsai collection, Elandan Garden's collection, and useful bonsai inspiration to reach your inbox. This platform is fully customizable so you can receive updates at the frequency and in the format that you prefer most.
    1.  If you already were a subscriber to receive new posts via email, especially if this post reaches your inbox successfully. If you have issues subscribing, please let me know!
  2. As always, submit your trees for critique or advice here. I need new trees for the next Bonsai Buds episode! This will be my next project.
  3. Seeds and bonsai guide for sale! Catalpa will be added to my Etsy list later this winter, and some others... 
  4. If anyone wants/needs someone to talk about the vaccine, feel free to email me. By day I am a microbiologist working on vaccine development & I've had the vaccine for several months now, as have many of my friends and family. Of course, I encourage you all to talk with your doctors about this but feel free to use me as a resource as well. The vaccine is our path back to a healthy country for safe reopening of the economy. With the rise of delta variant getting people sicker - even young adults - and additional data pouring in on vaccine efficacy, the situation is becoming urgent in many areas of the country.
  5. Upcoming Columbus Bonsai Society events
    1. 8/15/2021 - Club Potluck
      1. Bring a tree to work on and a dish to share.
      2. You can also bring trees/supplies to sell.
    2. 9/6/2021 - CBS @ Upper Arlington Labor Day Arts Festival
        1. I'll be running the booth. Come say hi!
    3. 9/18-9/19/2021 - CBS Annual Show @ Franklin Park Conservatory
Stay safe and bonsai on!

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