Crushed eggshells in the planting hole prevent blossom end rot.
Refuted
Eggshells in the planting hole won't stop blossom end rot. BER is a calcium-transport problem caused by uneven watering, not a soil-calcium shortage — and eggshell calcium takes seasons to break down, so it isn't available this year regardless. Water evenly, mulch to steady the moisture, and soil-test before adding anything.
What is actually known
Blossom end rot is not a soil-calcium shortage — it is a calcium-transport failure inside the plant, driven by uneven watering (calcium rides the water stream, so erratic moisture starves the fruit tip even when soil calcium is fine; see the Epsom-salts belief, B-004). On top of that, eggshell calcium is locked in slow-dissolving calcium carbonate that takes seasons to break down, so it is not available to this year's fruit anyway. Two independent reasons the eggshell-in-the- hole trick can't work. The real levers are even watering and mulch, and a soil test before adding any amendment.
Evidence: not yet confirmed against its 1 source.
what this rests on - one pointer
Iowa State University Extension, Yard & Garden, 'Blossom End Rot' (read 2026-07-14): 'This is a problem born of calcium deficiency, most often the result of erratic watering'; 'Adding calcium to the soil is generally ineffective' — so adding eggshell calcium to the planting hole does not address it (and eggshell CaCO3 is slow to become plant-available besides).
When would that grow at your place? →
Cite this page
Milpa Gardens. "Crushed eggshells in the planting hole prevent blossom end rot." Evidence grade: Refuted. https://milpa.garden/beliefs/eggshells-blossom-end-rot-eggshells-tomatoes/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.