Answer: I'm not convinced that the cast iron pot leached enough to kill your plants. However, the pot has the potential to absorb and radiate enough heat to make your impatiens extremely uncomfortable. Impatiens grow and perform best in cool temperatures and moist soil. If the weather has been hot, they can get stressed. With additional heat being released at night, the stress may have been too much. Try planting again (when the weather gets cooler). You might also try simply planting small pots of impatiens in the soil in your cast iron pot rather than planting them directly into the soil. This way you'll eliminate any possibility of any leaching substances from affecting the roots of your plants.
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