The micronutrients, which are found in the soil, are iron, zinc, molybdenum, manganese, boron, copper, cobalt, and chlorine.

All 17 elements, both macronutrients and micronutrients, are essential for plant growth. Most of the nutrients that a plant needs are dissolved in water and then absorbed by the roots. Ninety-eight percent of these plant nutrients are absorbed from the soil solution and only about 2% are actually extracted from the soil particles by the root. Most of the nutrient elements are absorbed as charged ions, or pieces of molecules (which are the smallest particle of a substance that can exist and still retain the characteristics of the substance). Ions tend to be able to dissolve in water.

MICRONUTRIENT OUTLINE

The majority of the micronutrients are not mobile within the plant; thus, deficiency symptoms are usually found on new growth. Their availability in the soil is highly dependent upon the pH and the presence of other ions. The proper balance between the ions present is important, as many micronutrients are antagonistic to each other (one will cancel out the effect of another). This is especially true of the heavy metals where an excess of one element may show up as a deficiency of another. If the pH is maintained at the proper level and a fertilizer which contains micronutrients is used once a year, deficiency symptoms (with the exception of iron deficiency symptoms) are rarely found on indoor plants. Many of the micronutrients are enzyme activators.

Put more simply, some of these micronutrients are needed to maintain a healthy plant, and I imagine will probably help to keep flowers fresher for longer.

Iron (Fe) Absorbed as Fe++, Fe+++. Iron deficiency: Interveinal chlorosis (discolouring between the veins) primarily on young tissue, which may become white. Fe deficiency may be found under the following conditions even if Fe is in the soil: Soil high in Ca, poorly drained soil, soil high in Mn, high pH, high P, soil high in heavy metals (Cu, Zn), oxygen deficient soils or when nematodes attack the roots. Fe should be added in the chelate form; the type of chelate needed depends upon the soil pH. Iron toxicity: Rare except on flooded soils.

Zinc (Zn) Absorbed as Zn++. Zinc excess: Appears as Fe deficiency. Interferes with Mg. Zinc deficiency: "Little leaf," reduction in size of leaves, short internodes, distorted or puckered leaf margins, interveinal chlorosis.

Copper (Cu) Absorbed as Cu++, Cu+. Copper excess: Can occur at low pH. Shows up as Fe deficiency. Copper deficiency: New growth small, misshapen, wilted. May be found in some peat soils.

Ok now for the juicy part, what is the composition of a penny?

Following is a brief chronology of the metal composition of the cent coin (penny):

• The composition was pure copper from 1793 to 1837.
• From 1837 to 1857, the cent was made of bronze (95 percent copper, and five percent tin and zinc).
• From 1857, the cent was 88 percent copper and 12 percent nickel, giving the coin a whitish appearance.
• The cent was again bronze (95 percent copper, and five percent tin and zinc) from 1864 to 1962.
  (Note: In 1943, the coin's composition was changed to zinc-coated steel. This change was only for the year 1943 and was due to the critical use of copper for the war effort. However, a limited number of copper pennies were minted that year.)
• In 1962, the cent's tin content, which was quite small, was removed. That made the metal composition of the cent 95 percent copper and 5 percent zinc.
• The alloy remained 95 percent copper and 5 percent zinc until 1982, when the composition was changed to 97.5 percent zinc and 2.5 percent copper (copper-plated zinc). Cents of both compositions appeared in that year.

So, for most of the time that a penny has been around it had a high copper content. I'm not a plant physiologist, but I would imagine that water generally is low in copper, and putting a penny in the bottom might just give sufficient copper ions to extend the life of the tulip flowers. Or, maybe the water is very high in iron, and the little bit of copper that comes off the penny helps to counteract the effects.

However, there is probably little point in doing that now unless you use pennies from before 1982. There are commercial cut-flower micronutrient mixes available. One that is available here in New Zealand is Chrysal.

Hope this helps answer you question a bit. I also hope that I am on the right track. By the way, the story about the penny is really quite interesting. I've left a few more links to the penny pages below if you are interested too.

Happy flowering from Astrid