The old Japanese adage is to water your bonsai tree three times; once for the pot, once for the soil, and once for the tree. By going back and forth over your collection three times it allows the water to soak into the soil and the pot and leave water for the tree to take in.
Watering your bonsai tree is a tricky thing to get a handle on, even in the best conditions. When It's 100 degrees out, it's a whole other matter. During the summer, bonsai trees are in maximum capacity mode. They're not putting on new growth like they did in the spring. The roots have all the foliage they can handle and they're not taking on any newcomers.
Things to remember:
- Some bonsai species require "full sun." Full sun does not mean blazing, all afternoon, direct July sun. Even full sun varieties of bonsai appreciate afternoon shade in the summer.
- Don't forget about soil temperature. A bonsai lives in a very small world. Its pot and the soil temperature can rise to very high degree when left in the sun, cooking its tender roots like a pot of linguini.
- Avoid the temptation to water your bonsai tree just to "cool it down." Wet foliage can increase the sun's rays - each drop acting like a little magnifying glass that ultimately does more damage than good. Besides, the water belongs in the soil, not on the leaves.
- Watch where you point that thing. The water in a hose laying in the sun can reach temperatures of scalding levels. One blast of hot water to your bonsai tree, whether on the foliage or into the soil could kill it. Turn on the hose and give a nearby ant pile a good dose of boiling water for a few moments before you water your bonsai tree.
- When it comes to water, it's always slow and steady. When soils are dry, you can water them until the water flows over the top of the pot, yet only effectively wet the top 1/4 inch of soil. Dry bonsai soil is a little bit like the dry sponge next to the kitchen sink. Initially, the water runs off the sponge and does nothing to saturate it. It's the second and third application of water that does the trick.