The most important part of taking care of your Bonsai trees is watering. How often a tree needs to be watered depends on several factors such as; species of the tree, size of the tree, size of the pot, time of year, soil-mixture, and climate. I can’t tell you how often you should water Bonsai without knowing what kind of tree you have. However, understanding a few basic guidelines will help understand and identify when a tree needs to be watered.
As mentioned previously, how often a Bonsai tree needs to be watered depends on many factors, and providing an exact guide is not possible. Instead, you need to observe your trees individually. The following guidelines will teach you what to look out for and how to identify when to water your Bonsai:
It doesn't matter what time you water a Bonsai. Some experts do advise not to use cold water when the soil is warm from being in the sun because it cools the tree too. Although this is something that you should keep in mind, you should water your tree as soon as the soil gets slightly dry, no matter what time it is.
When you've determined that the soil is slightly dry and the tree needs water, make sure to thoroughly soak the entire root system. Keep watering until water runs out of the bottom drainage holes, and possibly repeat the process a few minutes later.
Pour water from above using a watering can with a fine nozzle to prevent the soil from being washed away. If you keep your Bonsai indoors, you can place your tree in your kitchen sink and water the tree thoroughly, before placing it back. The best water you can use is rainwater because it doesn't contain any added chemicals, but when this is not readily available there is no problem in using normal tap water. There are some good automated watering systems out there, but they are quite costly.