Don't you water a bonsai like any other plant? The answer is absolutely not. Bonsai are very particular and specific and how to treat them will depends on lots of factors including environment and climate.
There are lots of different species of bonsai that use water at different rates, they grow at different rates in their different growing cycles. Deciduous, non-deciduous - all bonsai are not the same. There are no set cycles with bonsai and they should be attended to when it is required.
Watering - never let the compost dry out. That is the quickest way to kill a bonsai. The trees and plants in the ground adapt to their environment, your bonsai cannot do that as they are in such a small scale, that the things you do, or don't do have a big impact on it. In Japan it is said that it takes 3 years to master the proper watering of a bonsai.
Under-watering harms a bonsai far more quickly than over-watering. It is very important to take careful note of the condition of the compost, make sure it is not dried out.
The roots of a bonsai need oxygen to breathe - water comes into contact with the roots and provides oxygen, it flushes out all the by products and in exchange gives fresh air and oxygen which nourishes the plant. If you give too much water the plant will literally suffocate - the fine root hairs cannot breathe and it dies through too much oxygen.
So how can you tell how much water is the right amount? Well, if you are re-potting, if you have over-watered the fine root hairs will have turned black and have rotted and died.
Signs that you are watering incorrectly are - loss of vigor, no longer vibrant and healthy, but looking tired - foliage turns yellow and drop - the smaller branches wither and die away these are all good indications that you are not watering correctly.
So what can be done to remedy this? Cutting away the black roots will help. Rotten roots foster bacteria that kill the plant, so cutting the old rotten black roots away will help restore a more friendly eco system and help the plant to recover. Take care not to damage the healthy roots as this will impede recovery. More importantly you will need to change your watering habits!
How often do you water? Never on a set routine. Temperature changes and changing environment mean that you need to adapt to what your bonsai needs. Bonsai only have a small root system and can dry out very quickly, you must keep a careful eye on the needs of each individual plant. Your plant may have damp compost on top, but below be drying out. Each species bonsai plant will use water at different rates according to their living conditions, and must be checked daily.
A tip to help you find out what is going on beneath the surface is to put a wooden toothpick into the soil and leave it there. When you check next the toothpick will help you to see if the compost below the surface has dried out, by looking at the lack of dampness and this will help you assess how much water you need to use.
You need to be able to adapt your routine to the needs of your plant and never underestimate how important watering is.
Do you know the correct way to care for your bonsai? Read more great articles by Paul March about techniques to help improve your bonsai. More articles on bonsai care and information on reviving bonsai trees to help you enjoy your bonsai.