A penny for your thoughts? The copper contained in these coins could be good for your plants… in moderation. Copper is a key component in various enzymes that are essential to healthy plant function. Some of these enzymes help build the amino acids that make up proteins in the plant. Other copper-fueled enzymes are used in photosynthesis and respiration. A plant’s copper needs are highest during the initial growth stage.

Most soil has sufficient copper content, especially soils with a high clay content. However, high pH levels (over 7.5) can limit its availability to plants, as can the presence of other metals like iron and manganese. Compacted soil can also affect copper uptake, because the mycorrhizal fungi that bring it into the plant are unable to live without ample oxygen. Because copper is not mobile in plants, symptoms of copper deficiency show up in new growth first. Curled leaves, excessive branching or chlorosis (loss of green color) are all signs of copper deficiency.

Copper has antifungal properties that make it a key ingredient in some fungicides. Be very cautious, though: this is one of those nutrients that you do not want to overuse in the garden. Always perform a soil test to confirm the need for added copper. When too much copper is taken in by plants, it can stunt growth and give plants a bluish color. Too much copper in the soil can also lead to reduced seed germination and uptake of iron. And since it is insoluble, it persists in the soil, making it difficult to reverse copper soil toxicity once it occurs.

Oh, and just to be clear - don’t go grinding up pennies for your fertilizer. Today’s pennies are only copper-plated–they’re made mostly of steel.