I don't wash my shells, Don't see any need too, I just put them in a gallon zip lock bag and crush them and put them in the freezer during the winter so I have them when it's time to plant, I put a good handfull in the ground with the plants.

I crush them once by hand and toss into the kitchen compost. I see a few bits in the compost but rarely see them in the garden.

They will raise the pH and soluble calcium levels. Actually I quit composting mine last year after seeing that my soluble Ca numbers were very high.

Impossible to say how many pounds of powder per square yard or flower pot is the 'right' amount. "How much is too much" depends on how many eggshells vs. how much land area you're putting them on over what time period, and your soil pH. Probably more likely to overdose with the house plants than the garden, due to the small volume of completely contained soil.

Any calcium that egg shells may have will not be available to plants for a year two in the soil and you would need something like half a ton per acre to make much of a change.

Grinding the shells will decrease the time required for the shells nutrients to be available to the plant and increase the amount of nutrients available for that time period since the surface area of the shells is increased therefore decomposition from contact with natural elements occurs at a greater rate. I would apply them directly to the soil, but their could be a loss of nitrogen during the decomposition period.

Grinding the shells will decrease the time required for the shells nutrients to be available to the plant and increase the amount of nutrients available for that time period since the surface area of the shells is increased therefore decomposition from contact with natural elements occurs at a greater rate. I would apply them directly to the soil, but their could be a loss of nitrogen during the decomposition period.

Keep in mind that the most common limiting nutritional issues for soils are deficiency of N, and excess of Ca and/or a deficiency of Mg. W/o a soil test, it's impossible to know if your eggshells are a help or hindrance. Ca is rarely deficient in nonagricultural soils, and an excess has the same potential to limit as a deficiency.

Al

If you have chickens, egg shells make the best grit.