Chelated iron versus scrap metal to correct iron deficiency
In areas where the top soil is deficient in iron, it is necessary to add it when you plant trees, shrubs, or roses until the roots go to the level where iron is available. Chelated iron sold at nurseries is expensive, but it works fast. Plants have the ability to absorb iron in other forms, and you can prevent a deficiency by adding material which will become part of the soil in the form of iron oxide (rust). When digging a hole for planting, you can throw crushed cans, bottle caps, old nails, and other scrap metal into the hole. In two or three years, the tin cans will have rusted away completely, and you may dig in some more later. Old nails and bottle caps can also be stuck into flower pots.
Make sure the cans are not aluminum. When in doubt, test with a magnet.
The old method of driving a nail into the truck of a tree is not of lasting benefit.