Myth Buster! Several have mentioned this method recently, but the science does not support this for healthy plant growth. Tums are 40% elemental calcium, but the source is calcium carbonate - with a pH of 9, serving as an antacid and also the same ingredient as garden lime. Tomatoes are going to grow best at a 6.5 to 6.8 pH. If calcium is needed, gypsum is calcium sulfate, and will not raise the pH. If you have very many plants, this would be much more cost effective as well. Most of our Oklahoma soils have sufficient calcium, but it is more of an availability issue. pH can affect calcium availability, as well as uneven watering. Save the antacids for medical use and try the tips below.