March 23, 2021

Repotting The Monster Mulberry - Revisiting the Basics

Source material: 3/16/2021

            After a few weeks of being buried in snow, last week my larch seedlings started setting off alarm bells with green needles bursting from their dormant buds. "REPOTTING SEASON IS HERE, GET YOUR A@# INTO HIGH GEAR!" - is probably what they were telling me. I quickly reorganized my work and homework schedule to make the past week as bonsai-focused as possible for this narrow springtime window. While spring is also the perfect time for planting seeds, today we will discuss the first of a handful of major repots I did last week. Today's repotting report focuses on one of the largest trees in my collection at the moment - a yardadori/landscape origin mulberry tree.

            This repot was done with the help of my friend in the Columbus Bonsai Society, Kevin. Kevin grew up around Portland, Oregon and moved to Ohio just a year or two before I moved back. It's been great having another PNW native person to talk bonsai with. Thanks for your help building the grow box, Kevin! Y'all will definitely see more of him in future projects on this blog 😉.


First up: The Monster Mulberry with a falling apart plastic pot (hence the need for the repot).

I. Repotting Basics Recap

            As I discussed last year in my article "When to Repot", it is generally best to repot and prune roots before buds and leaves open in spring. If you disturb/prune too many roots after a tree has already opened its leaves, the tree will be at much greater risk of dieback or complete death because when leaves are open the tree can do much less to regulate its water loss. One particular yardadori plum I transplanted just a few weeks too late after the buds opened died so that this lesson would be ingrained in me. Sorry plum :(. Anyways don't repeat my mistakes and get repotting if you see buds opening; or, if you must delay/adjust roots outside of spring, do so by slip potting with minimal root pruning only! Young trees may tolerate more abuse and less precision, but especially when dealing with collecting/transplanting old and fragile trees, I encourage you to be gentle and be strict with this rule. Use your judgment and experiment to find what works and where the limits are with different species in your climate.
            Repotting at this moment for this year in Columbus (before the emergence of leaves but after the end of freezing temperatures that kill new roots) allows the plants to have more control over their water needs while regrowing roots because roots will regrow up to and including when leaves emerge. I also suspect plants could slow down their leaf emergence in response to root/water intake loss if needed, but bud opening is a preprogrammed activity to some extent. When transplanting or repotting, always consider that water intake must be able to match water loss and sugar production+stored sugars must exceed sugars needed for repair and regrowth. These are the fundamental equations of plant biology that we manipulate in bonsai by our pruning and growing cycles. Mild root pruning should not skew these equations out of balance too much, but one of our cases of more severe root pruning from this spring warrants additional consideration using this framework.

    Ranting aside, now for the big tree.

II. The Monster Mulberry

            This is a huge prebonsai yardadori that used to be a city tree. After substantial dieback (see the deadwood below), the city no longer wanted it and the previous owner dug it up. 4 years ago - before I even had my first car - I bought this tree via the Facebook auctions group since they would conveniently ship it to my front door. In that time, I have not repotted the tree or done much styling. Instead, I've focused on letting it grow new branches to heal scars and observing it, but as the pot is now falling apart (see the first image), it now demands my attention.

The Monster Mulberry, as photographed in January 2017 when we first met. Photos taken in my old college rental house 😂. I've always imagined this as the front of the tree.

Monster Mulberry rearview, January 2017.

Rearview pre-repot 2021.

Side view pre-repot 2021.

The other side view; with the cracking plastic in its full glory. pre-repot 2021.

I use 2:1:1 mix of aged pine bark: lava: pumice for deciduous trees.

            This tangent requires a bit more explanation before any of y'all attack my soil choice. I prefer to use aged pine bark as the water-retentive/organic part of the mix rather than the Japanese specialty clay-type soil "akadama" because it is dramatically cheaper for a budget-restrained Ph.D. student like myself, but also because I have seen it to be effective in developing show-worthy bonsai. My former bonsai teacher, Dan Robinson, has been using aged pine bark on his trees for decades with great success at Elandan Gardens with over 300 mature specimen bonsai. There is great controversy out there in the bonsai community about whether his methods are outdated, but the trees he produces with his methods are impressive regardless of where you land in that debate. Just remember, using aged pine bark rather than fresh mulch is important because the first year of decomposition is nitrogen negative - the bacteria and fungi breaking down the pine bark will consume more nitrogen than they release. 

Don't let moss grow on top of wood unless you're okay with the wood getting soft and decaying. The bottom sections here definitely need to be addressed. Moss on top of the soil is fine though to keep the top layer of the soil moist and usable for roots.

            The old soil was mostly pumice and gravel but upon chopsticking a bit deeper, we found a large heap of muddy/clay-y soil in one section of the rootball which we completely removed. Tangled exterior areas of other portions of the rootball were teased out so roots could be pruned, but since we disturbed the clay section so thoroughly and made some big cuts, we did not disturb the other section of the core rootball as much to be cautious.

From here on out the pictures start to get a little blurry due to the sun setting and my camera struggling in the low light. Please excuse the focus!
This left side was the area with lots of clay. Gently wiggling the chopsticks around to remove clay without damaging roots definitely slowed us down.

You can see roots in the muddy section are long and without much ramification - this is because of the lack of oxygen in this area which did not encourage fine root growth.

This was my first time successfully making a wooden grow box. Luckily Kevin already had all the tools and experience we needed to build a sturdy box that will support the tree's weight for several years.

We finished the repot late at night.

I love this tree's deadwood, but some parts need to be further cleared of rotting wood and/or treated with wood hardener to preserve it.

One day later... post-repot 2021.

This might be the future front. I planted it a bit off to the side in the box though so one of the surviving roots could have more room to spread out. It is still a training pot after all!

Rearview post-repot 2021.

            Is Monster Mulberry a fitting name? With a bit more deadwood work, the monster will shine even more. It never ceases to amaze me how spending the time to focus on a neglected tree can make it one of my favorites in a single day.

III. Blog Announcements

  1. Submit your trees for critique or advice here. I need new trees for the next Bonsai Buds episode! Guest announcement TBD.
  2. Contact me if you ordered seeds from me last year and they did not germinate. Now is the perfect time to plant!
  3. 6 New seed types are now on sale on my Etsy store with my 10-year bonsai growing guide. I have some unique ones such as Bloodgood Japanese Maple, Shore Pine, and more. See if any catch your interest. 

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