Yet Another Watering Problem…
Probably the worst thing we might encounter when we have a hose in our hand is a tree that, when we think about it, has not dried out in three days of sunny summer weather. That ought to send off all kinds of alarm bells in your head. If none go off, install some.
First of all, don’t water the tree if you want it to live. Secondly, place it in semi-shade and mist it frequently. The roots are not working, they are not drawing up moisture. Usually what has happened is root rot: the small roots got crispy dry, then they got waterlogged, and now the soil is staying waterlogged and everything that was living is slowly decomposing. This is like a heart that just stopped pumping and the medics are scrambling for the jump-start. If those small rootlets don’t start growing out again soon, the tree will die.
Tip the pot up on a block to let the excess water run out the bottom of it. The pot must be kept a bit on the dry side, and water introduced by misting onto the leaves to get the tree going again.
This is one of those cases where prevention is worth it’s weight in platinum. Don’t let your trees get COMPLETELY dry, and be ever alert to those that are not drying out as you would expect.
Michael Hagedorn 
2 Comments
Great information but as a beginner I had two questions. I had a couple of trees last year that I thought needed water because of the hot weather. The top 3/4″ of the soil was dry but the bottom 2/3 of the pot was relatively moist. I watered these trees because I wanted the surface roots to have water but eventually lost them trees. I think the top layer was dry because of dry wind and sun but I believe the deeper roots had slowed down their need for water for whatever reason. This year I have put sphapnum moss on the surface and water less. This seems to work but I wanted your opinion on how to provide moisture to important surface roots (nebari) without drowning the rest of the roots at the bottom of the pot.
Second question: Is organic soil used in Japan for bonsai?
Christopher,
Good questions. What kind of soil are you using? That determines how you treat your top. With a coarse soil that is based on Japanese preferences, particles of primarily akadama and pumice, they layer their pots with different sizes from large on the bottom to smaller on top, finishing with a bit of sifted spagnum. This keeps the water level high in the pot, just as you suggest. Smaller particles near the top, maybe 1/8″ in a real hot/windy area, and spagnum on top of that is the trick.
I never saw organic soil used in Japan, but that does not mean someone wasn’t using it—
Best,
Michael