A frequently asked question by people new to bonsai is how much care does a bonsai tree require? We know that the daily care of bonsai takes about the same amount of time that feeding the family dog does. Each day some kibbles are scooped into his bowl and the water dish is checked to see if he needs water, and that’s about it. How hard is that? In the case of bonsai each day the tree must be checked to see if it needs water. If it does, it is watered. Again, how hard is that? The tricky part is consistency. If you don’t feed the family dog for several days, he will become very mad at you. If you let your bonsai go dry for several days, the tree may die. Of course, each year the bonsai tree requires a little more than just the daily care, and may be repotted and trimmed and wired as needed, but these activities are only performed once or, at best, occasionally during the year. The rest of the year is pretty easy.
Why is it that bonsai trees need to be frequently checked for water, whereas landscape trees can be left on their own all summer without water once they have become established? The simple answer lies in the feeder roots. These are structures at the very end of the roots and are responsible for slurping up water and nutrients that the tree needs. When the soil is moist, water flows from the soil into the tree. The flow of water is a gate which swings both ways. When the soil is dry water flows from the tree to the soil. Once water is lost from the feeder roots, they can become dehydrated. If water is promptly administered, the roots can rehydrate and no major harm is done.
However, the dry roots can quickly pass the point of no return, and then no amount of water will forestall death of the roots. If this happens, the tree has no means of securing the goodies that it needs to survive and the tree becomes essentially a cutting which needs time to grow new roots. While waiting for new roots to grow, the tree is constantly losing moisture through the leaves. It becomes a race between losing moisture and replacing lost moisture through new roots. In short, the tree is in big time trouble and the prognosis is not good.
On a hot day, the top few inches of typical garden soil can dry out. The landscape trees know this and bury their roots deeply into the soil. Even though the top few inches of soil are crispy dry, there is enough moisture in the deep soil to maintain the feeder roots of the tree.
However, in the case of the bonsai tree, if the top few inches of soil become crispy dry, that is all the way to the bottom of the pot and beyond, and that, of course, includes all the feeder roots. The feeder roots will dry out and die and generally the tree will give up and die before it can grow new feeder roots. This scene is aggravated by the fact that very loose soil mixtures are used for bonsai, which avoids root rot but dries out quickly. The moral of the story? Check your trees daily for water needs and, by the way, don’t forget to feed the family dog.