Hello,
If your Bonsai is one of the outdoor species, then the only time you need to be cautious is when the weather turns hot and dry, or when there is an abundance of rain. During normal summer months, you should water your Bonsai about twice a week, and if the days are extra hot, move the trees to shade.
Some people will use a drip or mist sprinkler system that waters the Bonsai without getting them too wet. If you live in a region that is prone to long, dry spells, then using something as simple as a water sprayer will help increase the humidity level.
Tips for Watering
If you are unsure if you are providing your Bonsai enough water, you can always lift the pot and feel the weight. Amazingly, once you become accustomed to the pots you use, you can generally tell how much moisture is in the soil simply by feel. Considering that the water accounts for about 25% of the overall weight, this is not difficult to do.
Another method is to keep a set of wooden chopsticks on hand. If you think the soil is dry, you can poke the chopsticks down into the soil. If they come out dry, then you need to water your Bonsai. However, if you notice moisture on the chopsticks, then you are still good.
One of the most important things you can do is learn the water patterns of your specific plant or tree. Since each has different drying times, this will help you determine the right amount of watering and the best schedule. While quick drying and frequent watering is exceptionally good for Bonsai, you do want to make sure you do not over water, which could cause root rot.
Thanks...!