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 (like species of tree, size of tree, size of pot, time of year, soil-mixture and climate), indicating that it is impossible to say how often you should water Bonsai. However, understanding a few basic guidelines will help you to observe when a tree needs to be watered.
As mentioned above, how often Bonsai trees need to be watered depends on too many factors to give exact guidelines. Instead, you need to learn to observe your trees and know when they need to be watered. The following general guidelines will help you to get Bonsai watering right:
- Water your trees when the soil gets slightly dry
This means you should not water your tree when the soil is still wet but only when it feels slightly dry; use your fingers to check the soil at around one centimeter (0.4’’) deep. Once you get more experienced you will be able to see (instead of feel) when a tree needs watering.
- Never water on a routine
Keep observing your trees individually, instead of watering them on a daily routine, until you know exactly what you are doing.
- Use the right soil-mixture
The soil-mixture greatly influences how often trees need to be watered, for most Bonsai trees a mixture of akadama, fine gravel and potting compost mixed together in a ratio of ½ to ¼ to ¼ should be fine. However, use a mixture that retains more water (by using more potting compost) when you cannot water your trees that regularly. Read the bonsai soil mixtures article for more information.
It doesn't really matter at what time you water a Bonsai. Some advice to avoid watering (with very cold water) during the afternoon, when the soil has been warmed up by the sun and will cool down rapidly when using cold water. Though this can be taken into consideration, it should always be clear that you should water your tree no matter what time it is, as soon as the soil gets slightly dry!
As explained previously, water when the soil gets slightly dry. When the tree does require water though, it needs thorough soaking so the entire root system is wetted. To do so, keep watering until water runs out of the drainage holes, and possibly repeat the process a few minutes later.
Water a tree from above using a watering can with a fine nozzle; this will prevent the soil from being washed away (see photos 1 and 2, below). Using collected rain water is better (as it doesn’t contain added chemicals), but when this is not readily available there is no problem in using normal tap water.