Bonsai Tonight

Repotting black pine in nursery soil

Posted in Bonsai Development by Jonas Dupuich on April 14, 2015

Sometimes during repotting, I feel like I’ve passed a point of no return. The feeling struck when I was working on a black pine this past winter.

Repotting black pine

After combing out the roots – there’s no going back

The pine – see Friday’s “Cleaning up a black pine” for a look at the tree today – is undergoing the transition from landscape material to bonsai. One of the more radical aspects of the transition happens in the pot – the switch from nursery soil to bonsai soil.

The first time I repotted the tree, I had to remove a lot of roots to get it into a smaller pot. This didn’t provide a good opportunity to change out much old soil as I wanted to keep the tree strong. Two years later, the tree was strong enough for a more invasive repotting so I went about bare-rooting half of the rootball.

Bare-rooting bonsai typically reduces vigor greatly and it can kill conifers. For this reason, it’s common practice to bare-root a portion of the rootball – maybe 1/3 or 1/2 of the rootball – one year and bare-root another portion in a subsequent repotting 1-2 years later. That’s the approach I took with this black pine. Here’s the tree before repotting.

Black pine

Before repotting

After removing the tree from the pot, I had to decide which side to bare-root. I selected the side with the least amount of roots. This reduced the stress to the tree – I could preserve more fine roots this way – and it left me with a solid chunk of soil that would help me anchor the tree in the pot.

When bare-rooting, I try to remove old soil without damaging the roots. This involves carefully combing out the roots with root hooks and chopsticks – a labor-intensive process. Depending on the condition of the old soil, I’ll sometimes rinse off the bare-rooted half of the rootball with water to completely remove the old soil.

Repotting black pine

The bare-rooted half of the rootball

Repotting black pine

The intact half of the rootball

Repotting black pine

Half-bare rooted rootball from above

When the rootwork is complete, I take care to ensure the intact part of the rootball stays together. After adding a drainage layer to the pot, I nestle the tree into place and make sure it’s centered and positioned at the right height. Once the tree is set, I begin adding soil.

Repotting black pine

After setting the tree

I used a chopstick to prop up a root that was growing downward. In this new position, it can form part of the surface roots.

Typically, the next step is wiring the tree into the pot. When working with exposed roots, however, I work in soil between the roots before wiring the tree into place to avoid crushing the roots.

Repotting black pine

After adding some soil between the roots

Repotting black pine

After adding more new soil – just a bit more to go

When the soil has covered the roots, I can wire the tree into place like I normally would.

If the tree is wobbly after wiring the rootball to the pot, I’ll add a prop or a guy line to help hold the trunk in place. The roots and intact portion of the rootball provided a good anchor for this tree so wire sufficed.

Black pine

After repotting

I began fertilizing the tree a few weeks after repotting and am now feeding heavily in anticipation of decandling later this spring. I’ll think about removing the rest of the old soil in a year or two depending on how the tree grows in the meantime.

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Time for a smaller pot

Posted in Bonsai Development by Jonas Dupuich on March 10, 2015

First develop the trunk, then work on the branches. That’s how I think about bonsai development. If the trunk has yet to reach its final size, I use large pots and encourage vigorous growth. When I’m happy with the trunk, I move trees to smaller pots and focus on refinement.

A number of my black pines turn 11 this year. A few have reached the desired trunk size. I’ve been slowly removing large escape branches and am now ready to move the trees to smaller pots.

In general, if the soil is good, it’s easy to use a smaller pot as the root ball will have fine roots throughout. If not, the tree will have to stay in an intermediate-sized pot until enough fine roots develop to support the tree in a smaller space.

Here are two of the 11 year-old pines I repotted this winter – both were container grown.

Black pine

Exposed root black pine – 11 years old

Black pine

After repotting

Black pine

11 year-old black pine

Black pine


After repotting – note how the trunk looks larger in a smaller pot

Yes, Northern California is in the middle of a mild winter and most of my pines are already growing. As I repotted these trees about a month ago, I can start fertilizing now to make sure they’re strong enough to be decandled come spring.

Ever wondered what it’s like to be a bonsai apprentice in Japan? For those who haven’t done so already, feel free to submit questions to Juan Andrade, the Costa Rican bonsai artist studying at Aichi-en in Nagoya, Japan with Junichiro Tanaka, via AMA scheduled for later today (Wednesday Japan time) at Ask Bonsai Tonight.

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Repotting a shore pine

Posted in Bonsai Development by Jonas Dupuich on January 3, 2014

The shore pine is kin to the lodgepole pine. Both are native to California and parts north, but the exact relationship is open to some debate (see Pinus contorta for details). Shore pine bark is great, if slow to develop, and the needles are relatively short. Not strong enough to withstand decandling, it can be trained like white pine varieties. In fall I remove strong shoots from the strong areas and leave the weaker areas alone. At some point before spring, I remove old needles from the strongest shoots.

I’ve been working on the specimen below for the past two years. As it hadn’t been repotted in some time, I changed the pot after removing the old needles.

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Shore pine

Current and last year’s needles

After removing (with scissors) last year’s needles

As I packed up my things the morning of the workshop, I grabbed a pot that seemed to be the right size without looking too closely at it. After working on the tree’s roots, I took the pot outside to clean it and noticed that I’d grabbed a fairly old Chinese container. A bit much for a growing pot? Possibly, but then what’s the fun of saving old pots for exhibits? As the size was right and I’d brought no alternatives, I went ahead and used the old pot.

After repotting

The old pot

I’ve been happy with the selection since bringing the tree back home, and as it’s a bit larger than the previous pot, the new roots will have plenty of room to grow.

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Tamping the soil into place

Posted in Bonsai Development by Jonas Dupuich on October 25, 2013

After wiring a bonsai into the pot and filling the pot with soil, I’ll usually give the whole a few gentle taps to make sure I did a good job with the chopsticks. A few gentle taps can quickly reveal faulty chopstick work as the soil will quickly settle in neglected areas. I usually tap at least two sides of the pot while securing the base of the tree with my other hand.

Settling the soil


Tap a little bit too hard and the soil can pop out of place leaving the tree loosely secured and requiring starting the process all over again.

For the last step, I tamp the soil into place with my hand. Many wonderful and miniature trowels are made for the purpose, but hands can work well too.

Settling the soil

Tamping the soil

Is this last bit necessary? Good question. I’ve noticed that when I water after repotting, the soil tends not to move around as much after tamping the soil like this, and for this reason alone I continue to do it.

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