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Weakened larches

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Post  ivillaCanada Sun May 15, 2022 3:51 am

Hi:
I have cultivating bonsai for over 15 years, but in the last two years I noticed that several of my old larches have been getting weak, specially the lower branches. Last year I tried to prune the top to promote growth in the bottom branches, but it is not working and the trees are getting weaker. Here are pictures of two of the weakened larches. Any ideas of what I am doing wrong and how to correct the situation are very welcome. Thanks.Weakened larches 20220511
Weakened larches 20220510
ivillaCanada
ivillaCanada
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Post  Marty Weiser Mon May 23, 2022 3:52 am

What is the soil condition and when did you last repot them? What are you using for soil?

I grow mine in akadama-lava-pumice typically about 2-1-1 since larch use lots of water. I repot about every 3 years. I lost a back branch on one about the same age as yours last year, but I think it may have been our abnormally hot summer and that side of the pot seeing too much sun.

Marty

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Post  ivillaCanada Mon May 23, 2022 10:09 pm

Hi Marty:
Thanks for your reply. My bonsai soil is granite, turface & bark 2:1:1. When I started to cultivate bonsai I was using granite, turface, bark and clay soil, about 1/4 each, but several people told me not to use the clay soil so I eliminated it from my bonsai soil several years ago. Now that I have used both, I believe that the trees were healthier when I was using some clay in the soil, so I am thinking in going back to using some.

I have most of my trees in full sun, but I was thinking in installing some shade to protect them from the hottest part of the day.

With regard to the repotting time, depending on the tree, some I repot every year if there are very active and growing and some I wait 5 years, but most about every 3 years.

I also noticed that the ones that are now in the "right" bonsai pot size seem to be getting weak compared to the ones that are a little over-potted. Do you use bigger pot size even in your refined bonsai trees?

Where do you keep your hardy bonsai trees during winter? I use a plastic greenhouse with all the windows completely open, so it does not get hot during sunny days, but it protect them from wind and rodents. The problem is that, since they do not get any snow or rain I have to keep watering them. I have been thinking about leaving them on the ground and surrounded by burlap to protect them from the wind.
ivillaCanada
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Post  Marty Weiser Tue May 24, 2022 2:45 am

Compared to yours mine are in somewhat oversized bonsai pots. I wonder if your soil mix might be a bit dry for larch. Pumice would be the low cost way to increase the moisture level (and it would also make the pots lighter). I went away from bark in my bonsai pots (I use it for growing developmental stuff) since I had what I felt were root rot issues. if by clay you mean akadama, I have found that high quality akadama is a very good soil component. However, I have not got to 100% akadama for deciduous trees as some advocate - I use 2/3 at the max and 50% for larch.

I have over winter my larch in refinement in my greenhouse where my target temperature is 34F (1C). It will get a bit warmer on warm sunny days, but not much above the ambient temperatures which rarely exceed 45F (7C) in the midst of winter. I have kept them on the ground with protection, but now use the greenhouse since I have it dialed in. However, it seems to be getting fuller of things that need the protection so they may go back out on the ground with good protection. I have seen -10F (-23C) here, but not for many years. 0 to 5F (-18 to -15C) or a bit warmer has been more common recently.

I think that protecting the pot from overheating in the midst of summer is more important than protecting the foliage. I grow Japanese larch (L. kaempferi). I worked with Western larch (L. occidentalis) and found that it was very susceptible to the roots overheating - the side of the box with a forest that faced the sun would die off year after year.

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Post  ivillaCanada Tue May 31, 2022 1:09 am

Hi Marty:
Thanks very much for your reply and recommendations. I believe that they are very valid. I have not seen the same kind of problems that I have with my larches, with other trees like junipers and cedars, so I believe that you are right. I will add some pumice to increase the water retention and may add some share to reduce the possibility of pot overheating.

When you leave your trees in the greenhouse during the winter, how often do you water them?
ivillaCanada
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Post  Marty Weiser Tue May 31, 2022 3:02 am

I water the trees in the greenhouse about once a month, more often as the temperature is higher and there is more sun and perhaps a bit less frequently if it has been cold and dark so they use less water even though they are above freezing. I have shade cloth over the greenhouse and it has multiple layers of plastic so even direct sun is diffuse.

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