Unfortunately, there is a divide in the bonsai world at least as big as the Grand Canyon. On one side are the folks who grow azaleas so lushly that they have to whack the daylights out of them each year to prevent them from becoming a huge bush. On the other side of the chasm are the folks who provide a sterile and harsh environment for azaleas where the cold winds of death blow through the desolate land. Why is it that some folks can easily grow azaleas and others have no success at all in growing them?

There are many reasons why trees fail to grow for us, but for many of us who live on the wrong side of the chasm, the main culprit is the shimpaku juniper. More often than not, we started our bonsai adventure with a shimpaku juniper. These are endearing trees that can tolerate a fair amount of unintended abuse, and patiently wait while we learn how to manage necessities of bonsai life like proper potting soil, water and fertilizer.

As our collection grows, we add other species of trees, and we apply all we have learned about shimpakus to the new trees. In most cases, this works splendidly. But there are a few cases where this assumption fails, notably for azaleas. Azaleas have requirements that are distinctly different from shimpaku junipers, and if you try to grow them using the cultural conditions that you would use for shimpaku, you are doomed to failure. Recognizing this difference is the line between success and failure.

As usual, it is all about roots, and specifically, about keeping the feeder roots alive. As with all bonsai, the feeder roots will die when they dry out. In nature, the roots of shimpaku junipers grow deeply into the ground, and as a result, the roots dive to the bottom of the pot when a juniper is placed in a bonsai pot. They like sun, and during a hot day, the top half of an inch or so of the potting medium can dry out. Most of the feeder roots are down at the bottom of the pot, and the dry surface does not bother them. As long as there is at least a little moisture at the bottom of the pot, they will survive without damage. In short, for most bonsai, the most critical area of the pot to be kept moist is the lower third of the pot, where most of the feeder roots are located.

The ancestors of satsuki azaleas grew as understory plants in the forests of Japan. The soil is hard and impenetrable, and is covered with a layer of leaf litter. The feeder roots of the azaleas grow on the surface of the soil under the leaf litter. Further, the feeder roots are very fine and die very quickly if allowed to dry out. When an azalea is planted in a bonsai pot, it is not surprising that the roots reach for the surface of the potting medium. If an azalea is placed in the sun on a hot day and the top one half of an inch of the potting medium dries out, good bye feeder roots. In contrast with most bonsai, the most critical area for the medium to be kept moist for an azalea is not the bottom one third, but rather the top one third of the soil.

So, how do you prevent the surface of the soil from drying out? The answer is to place a layer of mulch on the pot to keep the top portion of the soil moist. Many azalea bonsai are grown with a layer of special sphagnum moss on top of the soil to protect it from drying out. Other forms of mulch also work well.

Azaleas are subject to root rot if the soil is continuously soggy wet. The choice of soil must be directed towards one that drains well, yet retains some moisture. The window between too dry and too wet for azaleas is a bit narrower than for shimpaku junipers, and a bit more on the wetter side.