We can do a lot better job of growing our trees if we understand what makes them tick and here is where a bit of plant physiology comes in. Let’s do three mental experiments which hopefully will shed some light on the subject.  In the first experiment we will plant our favorite bonsai tree in lovely soil and water it enough to keep the soil moist at all times. With a bit of fertilizer and sunshine the tree will happily respond by growing vigorously.  If we carefully look at what is going on with the tree we see that it has a marvelous plumbing system.  There are very fine feeder roots in the pot whose principle job is to slurp up water from the soil as well as nutrients.  The water is transported up the tree to the growing ends of the branches bringing the nutrients where they are most needed.  Much of the water is then lost by the leaves and this water is replaced from water in the soil by the feeder roots and the cycle continues. As the tree gets bigger it has more leaves and loses more water, and thus needs to grow more feeder roots to keep the water in the tree in balance.

In the second experiment we will pot our favorite tree in lovely soil and don’t water it for three weeks. We will observe that the leaves on the tree droop and then, as time goes by, turn brown and fall off.  At the end of three weeks our tree is about dead and then no matter of how furiously we water the tree it does not stave off death. So what has happened?  The lack of water in the soil does not allow the tree to replace water lost by the leaves, and the tree becomes dehydrated.  The tree attempts to make up for the loss of incoming water by dropping leaves. The feeder roots are severely stressed and if the tree is watered at this time the tree may slowly recover while it grows new feeder roots.  As the drought continues, eventually the feeder roots will die and the tree becomes toast, literally.  Once this point has been reached, no amount of water will revive the tree since with no functioning feeder roots, there is no way for the tree to take up water. In the real world, all this can take place in as little as a couple of weeks.

In our third mental experiment we will pot our long suffering favorite tree into lovely bonsai soil and into a pot with no drain holes. We water it normally and since the water cannot drain out of the pot, the tree ends up standing in a puddle of water. We see that our tree drops its leaves slowly and eventually dies. So what is happening here? An autopsy would reveal a surprising fact.  In spite of the tree sitting in a puddle of water, it died from dehydration.  How can this be? We live in a world of microbes and not all of them are beneficial by making bread, wine, beer and the other good things of life.  Standing water is an ideal breeding ground for bacteria and some of these wee beasties can cause root rot. Once the roots on the tree have rotted, there is no way for the tree to replace water lost through the leaves, and the tree becomes dehydrated exactly in the same way  as the tree we did not water in our second experiment. In the real world, this takes place more slowly than the case where we did not water the tree, but once root rot becomes established, it is difficult to treat and saving your tree is problematic at best.

So what does all this tell us?  The most important single factor in successfully growing our tree is to maintain conditions which lead to healthy roots. The lovely bonsai soil mentioned above is one that drains well but yet can retain moisture between watering. There are many different soil compositions that have been recommended in the past. One currently popular mix is one third each of lava, pumice and akadama (an expensive form of clay pellets mined in Japan).  Other mixes involve lava, fine gravel and pumice as well as about 20% of the mix being an organic ingredient such as fir bark or redwood.  Each of the various soil mixes has strong advocates, but truth be told they all can work well and beautiful trees can be grown using any of them.  The other condition is that the soil must be kept moist. so how much you water the tree is very important. Oh yes—be sure that your pot has a drain hole.