Here's some tips on how to get your bonsai through these horrifically high summer temperatures.
The first thing to do is throw some shade cloth over the top of your collection. If you have some nice shady trees in your landscape you can just move them under shade. Easy enough. If that's not an option, then just raid your linen closet and spread some sheets over the trees. Come on, everybody has old sheets that can be repurposed for bonsai shade. I prefer pale green or blue sheets. Pound some stakes in the ground. Anything will do to elevate the sheets off the canopy's of the trees...rebar, old broom handles, bamboo poles...Use some plastic ties to attach the sheets.
If you want something a little bit more sophisticated, get 3 or 4 joints of 1/4" pvc pipe, and a joint of 3/4" pipe. Cut the 3/4" into 8 to 10" sections. Cap one end. Pound the capped ends into wet ground (its easier to pound if its wet dirt) leaving a couple of inches out of the ground. Put one on each corner of your collection of trees. Take the 1/4" pipe, insert it into a 3/4" piece, bend it and put the other 1/4" end into the opposite corner. Repeat this until you have a series of hoops. Throw the sheeting over the hoops. Secure with plastic ties or clamps.
This is easy, quick, and flexible. You can put it up and take it down whenever you'd like. I like to shower the sheets for evaporative cooling. They will keep the trees 5 to 7 degrees cooler which is just enough difference to improve the quality of your trees.
Before I sign off I want to share another thing with you. If you're buying your el cheapo wantabe bonsai at big box stores, for heavens sake do the poor tree a favor and remove the gravel that's glued on top of the pot. Gads! That's a terrible thing to do to a tree. Its half dead before your even pay for it. You can't ever water it properly with that concrete-like layer of aggregate on top of the soil. Oxygen can't reach the roots. Oxygen to roots will be a topic I'll talk about at another time. I do alot of damage control here at my shop with customers who have purchased one of these trees and are having problems with it. I just had another couple in today asking for help. They had bought their tree from some mass marketer, I forget which one, and all the leaves were turning brown and falling off.
Growers who sell to mass marketers ship their plant products on pallets in the back of long haul semi trucks. That's the reason they glue the aggregate onto the top of the pots. The little trees would never make it to market if one piece after bumping around in the back of a truck for several days. When the truck would reach its destination, the dock worker would open the doors all they would find would be a heap of uprooted trees, soil, and broken pots. So they're glued. Its a cheap way to ship. However, the chance of getting a healthy tree is slim to none. When I ship a tree I hand wrap each individual tree and then they are wrapped again in bubble wrap. Sometimes with expensive, older specimen trees they have a third wrapping of single walled corrugated cardboard. When I prepare my trees for shipping they are wrapped for nuclear attack. So anyway, take the clued gravel off the potting mix. The tree just might recover.
So that's it for today. I'm signing off. Take care and remember...Promote Harmony...Grow Bonsai.