Copper plays a number of roles in plants. It indirectly serves as a catalyst in chlorophyll production. It is also involved in manufacturing lignin, the substance that gives plant cell walls strength.
However, copper is of particular importance to cereal crops because of its role in reproductive growth and grain production.
Animal manure and coffee grounds are plant-safe natural sources of copper.
Copper sulfate is approved for organic use. However, while it can occur naturally, most of the copper sulfate used in gardening and farming is actually man-made.
Some soils are naturally copper deficient, particularly sandy, peaty, or acidic soils.
Grains such as wheat, barley, oats, and flax are particularly sensitive to copper deficiency, but this problem can also occur in vegetables, particularly lettuce and onions. Legumes can also present symptoms.
The symptoms of copper deficiency in plants include:
- Cessation of growth.
- Overall blue-green color fading to yellow in vegetables and corn.
- Yellowing and stunting of new leaves on corn.
- Leaf tip twisting and death.
- Delayed or absent flowering or grain production.
- Purplish-brown patches on wheat heads.
- Major loss of crop quality.
- Plant death.
Very few soils naturally contain toxic levels of copper, although plants grown on reclaimed mining soil may exhibit symptoms. In most cases, however, copper toxicity is the result of long-term use of fungicides.
Symptoms of copper toxicity in plants include:
- Reduced vigor.
- Severe wilting.
- Stunted growth.
- Pale green to white areas between leaf veins on mature leaves.
- Stunted roots.
- Reduced seed germination.
Copper toxicity is extremely difficult to correct, as this mineral is not water-soluble. Treatment mostly involves mitigating the effects of the excess copper. Keep soil pH near neutral and other nutrients balanced. Also take steps to reduce stress on soil microorganisms, such as adding organic matter and reducing or eliminating tillage. Of course, you will also want to stop using copper-based fungicides, as well.