A traditional favorite gardening container material is cast iron. Cast iron urns are beautiful and elegant, but are very heavy. Painted cast aluminum is a popular substitute because it does not rust and it is not quite as weighty.
In the deep south, the walls of metal plant containers capture heat in summer. They transfer heat to the soil within, to the detriment of the plants growing within. One way to prevent hot metal from damaging tender roots is to provide an insulation layer between the pot and the potting soil. I have tried several different strategies. The most effective insulator I have found is bubble wrap, the kind used for protecting delicate items during shipping. It is inexpensive, flexible, and malleable to fit the nooks and crannies of elaborate containers. Simply cut a piece of wrap that is large enough to line the inside of the container. Place the wrap around the outside container walls, being careful to avoid blocking any drainage holes. It is easily trimmed to size with scissors, so that there is no excess visible above the soil line. Add regular potting soil inside the bubble wrap layer, and – voila! – the soil will not become scorching hot because it is not in direct contact with the metal. The thin material does not reduce the amount of soil available to whatever plants you choose for your container.
Another tidbit: Reduce the amount of potting soil needed by large containers by adding a layer of pine cones in the bottom, before adding soil.
This iron urn is lined with bubble wrap prior to the addition of potting soil.
A green and white combination looks classy and cool, even in the heat. Container contents: Diamond Snow Euphorbia (a filler), Rosemary (a thriller), and a double Calibrachoa (a second filler). Not shown, an ivy with a white leaf edge (a spiller). The Rosemary is evergreen, so it can carry over to anchor a winter container.
The completed planting. In a couple of weeks, the Rosemary will gain height and be a vertical center accent. The strong pine-like scent of Rosemary repels some insects. I’m hoping that it will keep mosquitos away from the seating area near this container, one of a matching pair.