We're having a heatwave, a tropical heatwave...

It is still Spring but tomorrow in Austin they are predicting we may reach 104F in the afternoon, which is root cooking temperature for potted plants in ceramic containers.  Pots in the sun will multiply the heat and reach killing temperatures to the roots if you are not careful. I thought it may be a good time to share my heat control measures.  I don't have an overhead shade cloth, and do not want to move trees each time the heat flares up, which is off and on all summer in Texas. The bonsai in the sunny spot of my yard need the intense solar radiation on their leaves to photosynthesize food, but can be damaged if the roots get too hot. My solution is to simply cover the ceramic pot with inexpensive Burlap cloth cut to fit which provides about 50% shade density. Think of it like your bonsai pots are protected by a straw hat.

Let's take this little Cedar Elm here

I'm not promoting a brand, but this is a 24 foot long roll I can buy at one of the big home improvement stores inexpensively.

Open it up and lay out the roll. Cut a strip which will not only cover the top, but which will also cover the sides, protecting the entire pot from heating up.

Take the square of Burlap and cut down the center, imagining where the trunk will fall when placed on the pot.  Then cut again sideways. This will allow little points of the cloth to gently wrap around the trunk.

I like to have the center-cut side to the back, so the front looks neater. Once it is placed, water your bonsai. The tiny fibers of the burlap will begin to stick to each other like weak velcro, holding the flaps together.

Here's another example. This pot has a very wide lip which catches a lot of sun and really heats up. In this case Burlap alone isn't enough to cool this pot. I start by cutting a piece of Burlap as before

Next I use coconut fiber to "pad" under the burlap along the edge of the pot.  I source this from the material used to line hanging baskets and I rip and pull it apart until I get thin sections of it, just thick enough to block the light, but thin enough to allow free flow of water.

The Burlap is then placed over the Coconut fiber both to hold it in place and to provide another layer of protection. 

Another type of bonsai which needs heat protection is a root over rock style tree.  In this case we need to not only shade the ceramic pot, but also the rock the tree is attached to.

I wrap the entire base of these trees with Burlap, like a little tent.

I will also go along and spray the burlap with water to moisten it and give the plant evaporative cooling during the heat of the day. While this heat fix may cover your beautiful pots, it's neutral colored, inexpensive, made from all natural products which can be composted after use, or even reused if they are in good enough shape the next year. I usually don't cover plastic pots or Mica, as these just don't capture as much heat as the ceramic vessels (place your hands on them in the middle of the day to test). Of course there are bonsai which have temperature tolerances which must be moved periodically, but for the sun-loving trees, especially my Texas natives, this has proven to be a great help to combat the summer heat.