the article is very interesting. I especially like the colored tires as a border! Now about the chemicals leaching into the ground. If you don't know what they are, how do you know that the tires leach? If they do leach, why put them around trees? Is it just an assumption?

Tractor tires make great sandboxes if you have kids.

These things hold a lot of planting mix or soil. If you are putting them on a non-permeable surface like a concrete sidewalk or patio, expect staining and discoloration of the cement. If you are using them on the ground, make sure that you won't want to grow anything in that spot after you take away the tire. It is still unclear just what chemicals leach out of the tire and into the soil.

Take a jig saw or saws-all and cut the sidewall out of the side of the tire you have facing upwards. This will double the usable area of the planter. The sidewalls cut easily and you can use the rings as collars around trees to reduce weed growth.

Think of growing potatoes in them. Instead of hilling the potato plants as they grow, just add another tire with both sidewall cut out and fill it with your planting mix. A good season will have you stack about 4 tires high. To harvest, simply remove one tire ring at a time and sift through the dirt to find your spuds.

Their black color will help to warm the soil in the early spring, too. That may get you planting earlier than your neighbors.