When we see, that the plant needs water we have to irrgate as follow: “watering till the soil gets completely soaked.” You will need: watering pot with little holes for maintaining soil in the pot, watering clusters with little holes in order to benifit from water pressure connecting a hose, trays to prevent getting furniture wet when place them indoor.
At first we irrigate one time the surface of the soil of the tree, this is necssary that the hummidity opens the leeks of the soil. After a few minutes, we turn to irrigate till the water gets out of the holes of the clusters.
The pot which accompanys the indoor Bonsai serve that the resting water doesent drip on the furniture. It is very important, that this plat after irrigation don’t rest with water. It is also important, that the level of the water doesn’t reaches the holes of the pot, because a tree, which is always wed, rots. On the other side, it exist Bonsai which can’t be irrigate following this indications, because the soil is to thick and the water supports by the sides of the pot and don’t penetrates the soil. In that case, its necessary to transplant and change the soil.
You can find plastic and ceramic trays that avoid damage on furniture. It is not recommended that the bonsai stay permanently with the roots submerged in water.
Another option is to fill the tray with volcanic stone or Akadama, and in this way creates, with the remaining water, ambient humidity.
In order for the soil of these bonsais to be well soaked we can put them in the plastic tray that accompanies the indoor bonsai, and leave them for about ten minutes. It is also necessary to water in this way the bonsai which by carelessness have remained dry and do not soak well.
Never irrigate with a vaporizer that is used to remove dust and give moisture to the plants.
They only moisten the surface of the pot and the water does not reach the roots. To sum up: You have to water with an appropriate shower or do it by immersion.
The small holes in the shower rose help bonsai absorb water better by imitating rainwater. You can find irrigation lances that fit the hoses or special showers for bonsai.
More information about watering cans, trays, hydrobons here.