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.
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.
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.
The bare-rooted half of the rootball
The intact half of the rootball
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.
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.
After adding some soil between the roots
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.
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.
I’m only now getting to some of the work I’d lined up for last fall. For some varieties like junipers, this poses no particular challenge. For pines, basic seasonal tasks like cutback and needle pulling get tricky once springs candles elongate as candles can break easily. I don’t mind working on pines that are only starting to move, but after the candles reach a certain point, I typically delay further work until decandling time. The tree below is a landscape tree reduced to its first branch. I’ve done little beyond cutback and decandling for the past few years, and wire has only been used to set the main branches.
Dense summer growth
After thinning to two shoots per branch
After removing needles
After wiring and pulling the branches down
I was surprised by the difference so little wire can make, and happy that two wires will suffice for now.
If you’re looking to plant seeds this spring, now may be a good time to do it. Considering how warm this winter has been in Northern California, January may have been a good time to get started, but either way it’s not too late to start now – weather permitting.
Many seeds benefit from scarification – treatments designed to pierce, damage or otherwise weaken the seed coating – and stratification – any means of providing artificial cool and moist conditions conducive to germination.
Pine seeds can be scarified by applying hot water. Stratification can be achieved by refrigerating seeds before planting (see Pine seed prep and Pine seedlings for an overview; treeshrubseeds.com provides details and specific instructions for different varieties).
Missing from my previous posts on the topic are photos. Here are a few shots of how I pack up the seeds after soaking them for 1-2 days.
Japanese black pine seeds – ready for the fridge
The moss is often sold as orchid moss or white sphagnum moss. I wet it and squeeze most of the water out before putting it in the bag. After a few minutes in the fridge, the bag fogs up.
Condensation in the bag
This year I’m planting red pine, black pine from Shikoku, and Mikawa black pine seeds.
Red and black pine seeds
After a full week in the fridge, I’ll plant them in a pot with bonsai soil and cover them with fine particles to keep them moist during germination. For details, see Planting pine seeds.
The basic premise behind developing material for bonsai is straightforward: first build the trunk, then focus on the branches. When building the trunk, encourage vigorous growth to thicken the trunk rapidly. When focusing on branch development, encourage less vigorous growth to ensure good branch density. Sounds easy, but there may be a bit more to it than that. When making the transition from trunk development to branch development, many bonsai will be quite vigorous. What are some good strategies for decreasing vigor? A reduction of fertilizer sounds like a good idea, but reducing it too much can weaken trees. And when developing pines, it’s important to keep them strong enough to withstand decandling. Reducing sunlight or water is another strategy, but to keep trees healthy, plenty of sunlight and water are required. The main thing is to avoid over-watering at this stage as it can lead to excessively long needles. One way to slow down pines is to shorten the spring candles. After the candles begin to elongate, simply break off some portion of the candle with your fingers. How much to break off depends on how long the candles are. Here’s an example on an 11 year-old black pine.
11 year-old black pine
First grab the section to be removed
Then snap it off
After reducing the longest candles
I could have reduced the longer ones a bit more, but I didn’t want to remove too much foliage at this point as I’ll have another opportunity to balance vigor come decandling time. Do note, candle pinching is distinct from what is commonly referred to as decandling. Whereas decandling is the removal of fully developed shoots in spring, pinching refers to the partial reduction of candles before the needles elongate. Once pines are further developed, it’s more rare for extra-long candles to develop as the vigor is generally better balanced in more mature trees. When these long shoots do show up, I snap them off.
Today marks post #600 – thanks for reading!