Repotting a trident maple: root-work

Tuesday, December 15, 2009

Repotting a trident maple: root-work

Part 3 of 5

I’ve seen it first-hand. Visting bonsai teachers come to town and whip trees into spectacular shape only to leave the trees’ owners with ticking time-bombs. Until a tree is in outstanding health, it’s a poor candidate for even the most basic bonsai tasks. Great bonsai work requires great health, and great health begins with the roots. If you hear otherwise, think twice before handing over the scissors.

All of this to say that repotting is serious business. Cuting too many roots can weaken or kill a tree – not cutting enough can lead to root rot or die back and prevent good nebari from developing. When done well, however, repotting can invigorate bonsai and give them the strength to recover from the most intensive styling techniques. That’s why repotting has always been among my favorite tasks. It’s an art unto itself, and it’s never failed to keep me interested.

Trident maple is best repoted in late winter or early spring. And while most deciduous trees are typically repotted before they leaf out, tridents can be repotted as long as the leaves are ruddy. Repoting this late can slow a tree down a bit, but if it’s in otherwise good health, it won’t skip a beat.

Root-work begins, in this case, with the botom of the rootball. To get to the bottom I have to tip the tree onto its side. After removing the tree from the pot I can see that the roots are loose where the sickle passed, but nice and compact on the other side. If I tip the rootball onto the side where the sickle passed, I can damage loose roots. Tipping the tree onto the untouched side can protect the rootball while I work on the base. This explains why I begin with the bottom of the rootball. If I start with the top or the sides, I’ll be exposing roots that could get damaged when I turn the tree onto its side.

Rootball – where the sickle passed

Rootball – the untouched side

I’m fairly picky about the tools I use when I repot. I’ve found that the rake below is perfect for combing out the roots on the bottom of the rootball. I work from the center and drag the rake outward keeping it paralel with the base of the tree.

Raking the base of the rootball (one year’s growth)

I try to keep the base as flat as possible when I work to avoid causing air pockets when I set the tree in the pot. Holding the rake at an angle or workng for too long in a single area can quickly create pockets, and in some cases, can weaken the entire rootball.

Working on small trees planted in good soil is fun work. It’s those two to three hour jobs that can try one’s patience – and forearms

After combing them out, I cut the hanging roots until the base is even. By leaving a little root sticking out from the rootball, I can help the roots integrate into the new soil. Cutting them flush can make it hard for the roots to penetrate new soil.

Root-work completed on the bottom of the rootball

Once the base is done, I can set the tree down and work on the top and sides of the roots. Bent-nose tweezers are great for this. I’m careful, however, not to hold the tweezers too high when I work. Steep angles can snag roots, causing them to snap or tear. By holding them at a lower angle, I can help the tips of the tweezers glide over roots without damaging them.

Improper twezer technique (angle too high)

Better twezer technique (appropriate angle)

You may have noticed that the soil is darkest near the surface of the roots. That’s evidence of the organic fertilizer I use – cottonseed meal, in this case. To improve the drainage, I scrape away as much of it as possible. When I’m done, I cut the roots evenly as I did on the base.

Root-work completed

It takes practice to learn how much to cut. When I dont have a teacher around to guide me, I tend to work with caution and pay close attention to how the tree comes out in spring. Over the years I’ve gotten much better at getting the results I’m shooting for, but I still find I have to pay close attention while I work.

Next up: Part 4 – Securing the tree in the pot.


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