Watering might seem like an easy technique, but it is the second most common cause of Bonsai-related problems. Under watering or allowing the compost to dry out completely will instantly kill or badly damage most trees; however over watering can just as equally cause ill-health and eventual death from root rot and disease.
The most important rule to remember is that trees should be checked for their water requirement daily but should only be watered as required. You should never water to a routine. This can lead to continually sodden compost which literally suffocates the roots.
The surface of the compost must be starting to dry out between watering. Then the tree can be thoroughly watered again. The time between watering can vary from 12 hours to 7 days depending on factors such as prevailing temperatures, wind and humidity levels.
Because of limited space in the confines of a bonsai pot, bonsai care can be quite difficult. The shallow containers limit the expanse of the root system and make proper watering practically an art in itself.
While some species can handle periods of relative dryness, others require near-constant moisture. Watering too frequently or allowing the soil to remain soggy can promote fungal infections and "root rot".
Sun, heat and wind exposure can quickly dry a bonsai tree to the point of drought, so the soil moisture should be monitored daily and water given copiously when needed. The soil should not be allowed to become "bone dry" even for brief periods.
The foliage of some plants cultivated for bonsai, including the common Juniper do not display signs of drying and damage until long after the damage is done, and may even appear green and healthy despite having an entirely dead root system.
When fertilizing bonsai you should do so with a water-soluble fertilizer once or twice per month during the growing season. Your choice of fertilizer may vary depending on the species you’ve chosen to miniaturize.
Apply fertilizer when the soil is wet and only before and during active growth. A houseplant fertilizer diluted from one quarter to one half strength will suffice.
Another area of bonsai that needs to be addressed by the beginner is repotting; a very straightforward technique if carried out correctly and at the right time. Most trees need to be repotted annually or at very least bi-annually in spring as the years new growth starts to appear. Trees that are not repotted will eventually lose their health and vigor.