How Much is Too Much? The Effects of Water Hardness on Green Onion Plant Growth


  • Tianna M,
  • Andra R,
  • Jennis S,
  • Pearl W


Similar to how people require minerals in order to maintain bone density and health,
plants require minerals so that they can build sturdy cell walls and develop healthy root systems.
Water hardness is understood to be a measurement of the concentration of minerals dissolved in
any volume of water. This study was conducted to test the effect of water hardness on plant
growth. Epsom salts were used to test how much Allium fistulosum (green onions) grew over
eight days at different levels of water hardness. We hypothesized that the addition of salts would
positively impact root growth and predicted that the onion placed in the highest salt
concentration would have the highest growth. Results were compared between the controls,
which were jars with green onions in soft tap water and other treatments at varying degrees of
water hardness. Results indicated that the onions that were placed in soft water without
additional Espom salts showed the most growth. The control had the highest mean growth of
roots at 1.35 cm. A possible rationale for this outcome was that the excess minerals used had a
negative effect by hindering root growth. One implication that the study has is that it can help in
future similar studies that examine green onions or other plants’ growth at different levels of
water hardness.