Our president Paul has provided a lot of good information regarding summer care. I would like to offer a few more tips/observations that might help.
1). On a hot afternoon, say 103 at 4pm; if your clay pot is sitting in the sun the external temperature of the pot can be over 120 degrees and the inside of the pot above 130 degrees. This heated clay is right next to the most tender shoots that are feeding your bonsai. These feeder roots are killed by the high heat and although the tree is getting plenty of water it is still fading away. When those root tips (they are the white or cream colored part right at the very end of the root) die or are damaged it does not matter how much water you put into the pot it aint going to get into the tree.
Here are some suggestions:
Obviously the best solution if it is possible is to move your bonsai into an area with afternoon shade. – Get some material from a swamp cooler (it looks like a big sponge) and cut it out to fit over the pot and will reduce the temperature. – Wrap the pot up (don’t plug up the drainage holes) with an old rag or towel and it will help a lot. – Some people put ice cubes on their bonsai soil in the hot afternoons. I have not done this but heard that it works ok.
2). The EID is requiring me to reduce my water consumption by 30%, so while I continue to water the bonsai every day I have started watering the stock plants every other day. Many of them are wilting or dying from lack of water. My plan has always been to place the trees into a fast draining material and water frequently. Now that I can no longer do that I am going to have to plant my stock trees into a denser material with more organic matter, and Akadama, in it to retain the water longer.
3). For our smaller bonsai we have placed them into/upon large (20″x30″) bakers trays with Hyuga, or other fired clay, about 1″ deep on the bottom. The little bonsai sit in this wet rock most of the day and they seem to do quite well. It is not uncommon for us to lift up one of the little pots and find roots 18″ long growing out of the drainage holes and through the gravel.
Finally, each of us is faced with cultural problems that are unique to our own bonsai collection. Is the property flat or sloping? do you face east or west? are there big trees where you keep your bonsai? how do you water? what fertilizer do you use? how big is the pot in relation to the tree? and on and on.
The proper care and maintenance of bonsai is a lifetime learning adventure. Enjoy and see you soon