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Shimpaku Health

Updated: Oct 8, 2020

Tree health is always something we strive for here at Aichien.  We try to keep everything healthy and strong so that we can apply the many different techniques of Bonsai and have the tree respond well.  Sometimes trees will become unhealthy and leaving them alone might not solve the problem.  In those situations we have to proactively get the tree back to health or the tree will continue to weaken and potentially die.  In this post, I will share a trick we use to keep a purchased Shimpaku that has root problems from continuing to die back during the Fall and Winter months.  As you can see from the picture above, some of the foliage is turning brown and if we don’t take care of the tree, more foliage and branches will continue to die during the Winter months.

Water in the Soil

One of the important aspects of Bonsai is how wet the soil is and how it affect the tree.  Depending on the tree, it may like the soil wet all the time or prefer drier conditions.  Understanding the trees water needs play a big part on how well the tree will grow and respond to Bonsai work.  In this particular case, we’re focused on a small twisted Shimpaku Juniper.  Have you ever thought about how much water they need?  Do they need as much water as say, a Trident Maple?

For the most part, conifers tend to like more drier conditions and deciduous trees like more wet conditions during the growing seasons.  During the dormant season, most trees do not like too much water.  Sometimes our Bonsais get too much water during the Winter, it may cause some root rotting issues and the tree will not grow as well during the next growing season.  To keep our trees healthy we have to check water levels daily and adjust the watering schedule accordingly to what the trees likes.  Just by how you water the tree can either add or take years away from its development.  I asked Mr. Tanaka how long it takes to master watering and he said, “10 years for the average bonsai person, 5 years if you’re good.”  It sounds unbelievable at first but after watering the yard for the last 7 months now, I understand what he means.  In the future, I will be writing a post about watering and fertilizing so I’ll explain more then.

Temperature’s affect on roots

Temperature is an important factor in root growth.  For most trees, the soil usually needs to be at least 70-75 degrees Fahrenheit (21-24 Celsius) before the roots will start to grow.  When the roots are too cold, the tree slows down and if the roots are too hot, the tree slows down. That’s why during the Spring and Fall months where the weather tends to float around the 70-85 degrees Fahrenheit (21-29 degrees Celsius) range, trees start to grow and can pull a great amount of water from the soil.

What’s the problem with this tree?

Mr. Tanaka and I looked at this tree and believe the reason why the foliage is dying back is because the soil is too wet.  This small Shimpaku is currently in 100 percent soft akadama.  I took a lot of care not to over water the tree but we were both worried that during the cold wet Winter, the tree may stay wet for too long and cause further damage to the roots.  The goal now is to keep the tree on the drier side so that the roots will stop dying off and the tree can make it through the Winter.  If you notice that your tree is not drying out like other trees, the tree may be weak and problems might start to appear if you don’t let the roots dry out.  On this tree, we noticed that the tips were browning out and slowly browning to the stem.  This is a sign that the tree is either too wet or too dry. Since the soil has been wet all the time, we knew the roots were weak and the tree has slowed it’s intake of water.  Here is what I did to help keep the tree drier for the Winter.

Wait a minute!

You’re probably all wondering why I would put 90 percent akadama into the soil when I was worried that the root ball was holding too much water?  If you actually did think that, then good for you!  You’re thinking!  If you didn’t think about that, don’t worry, you would have thought about it soon enough. ;o)

Why I used Akadama?

We all know that in a basic bonsai soil mix, akadama is the main ingredient that holds most of the water.  Other components such as river sand, lava and pumice holds little to no water.  You would think that if I wanted to keep the tree dry, I would put it in 100 percent pumice or lava?  The reason why I used Akadama (hard) is because it drains well and it keeps the root ball in a more balanced temperature zone.  Let’s break those two concepts down and make some sense of it.

Drains – since the hard Akadama doesn’t break down for at least two years of use, when the tree is watered, the water will drain right through the soil and out the bottom.  Since the rootball is more dense and compacted, the water is going to follow the path of least resistance and flow through the new good draining akadama.  The results being that the tree’s root ball will stay dry.

Temperature- akadama is not a solid piece of clay.  There are tiny little air bubbles inside the clay.  When akadama is heated, it tends to retain it’s average temperature for longer periods of time.  In this sense, we can keep the temp of the root ball more even instead of having it swing up and down dramatically depending on time of day.  If I were to put coarse river sand instead, once the outside temp drops, the root ball temperature will drop quickly.  The important part is to keep the overall temp of the root ball stable for as long as possible and avoiding temperature swings.

Another example

Say I was having this same problem but instead of Winter coming, it was Summer.  What soil would you put the sick tree in?  Coarse river sand or akadama?  During the Summer months, this technique is used also but the soil is switched to 100 percent coarse river sand instead.  Reason for the switch is that during the Summer, the days are really hot and the night temp only drops slightly. Using the coarse river sand will bring the root ball temp down to the optimum growing temp during the night and allow the roots to grow more.  If I were to use Akadama during the Summer, the root ball temp may stay too high for too long and not allow the tree more time to grow the much needed roots.

The future

Once Spring arrives, I will pull the tree out of the pot and do a real repot and clean out the compacted akadama in the core of the tree. That should help the tree grow very well and recover during the Spring.  In the Summer I plan to write another post about the tree in regards to picking a nice front and future design ideas.  The trunk is very twisty and there are so many possibilities to what this tree can look like in the future.

I hope this technique can help you all in the future in one way or another.  As always…

Thanks for reading

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