Did anyone ever hear of putting a layer of bubble wrap around the root ball in a pot to insulate the soil from the heat? If so, does it work? The soil in my containers gets so hot in Phoenix in the summer, even in the shade. If bubble wrap works I want to use it.
We have the same problem here. I sit my pots down inside one of those styrofoam flower pots you find at places like Big Lots. I find the insulation keeps the soil cooler in the summer and warmer in the winter. They don't hold up well and after a year or so they often look like they need a fresh coat of paint but even that is not too bad looking and easy to rectify. You can also find inexpensive double walled flower pots that help.
If it's clear, it will likely worsen the problem. Light will pass through. When it hits the pot, it will be turned to heat and be conducted through the pot material and into the soil, partially because the insulating wrap traps is there. If there was no wrap, the light would still turn to heat when it hits the pot, but the heat would not be trapped and would dissipate into the air. You would be better served to double pot and fill the space between the pots with something well-aerated (gravel, e.g.) and keep it moist during the heat of the day. Painting your pots white or selecting light colored containers can make as much as 40* (or more) difference in soil temps too, so choose light colored pots if possible. Wrapping them with a white material or tin foil (I know - classy, huh) is effective, too.
Most people don't realize that for most plants, just a few degrees difference in soil temperatures can have a very big impact on growth. I was just reading up on peach trees & discovered that best growth occurs at soil temps between 65-70*, with growth reduced by about 40% at 75* and 97% at 80*. Roses showed a similar pattern, but actually at temperatures even lower than the peach trees. For best vitality, we should try to always keep container soil temperatures below 80* whenever we can.
I'm in Phoenix. Actually I lined the inside of a huge clay pot with big bubble / bubble wrap. It held my plumeria for 2 years and it did well... at least it lived and thrived until I could get it into the ground.
I thank you all for the ideas of what to do to lower soil temps. In Phoenix summer I know they get a whole lot hotter than 80°! I will do some experimenting next spring and see what works best for me. Aguane: someone did tell me about the bubble wrap idea here in Phoenix, but, like Al said, I was concerned about doing more harm than good. It seems that it worked for you with a large pot though.
Note that he/she said the inside was lined, which would be much more effective because the light turns to heat at the container's surface and mostly dissipated into the air, while the wrap on the inside reduces conduction into the soil.
Oh, yes, that's is what I meant when I first asked. I wasn't clear what I was saying. I would put the bubble wrap inside the pot and then soil inside that and then plant in the soil. I wasn't going to put the bubble wrap around the outside of the pot! It would probably melt here in the 110 plus degrees of so many days of recent Phoenix summers!