Impatients respond to growing conditions by moving nutrients from older leaves to newer growing leaves if there are not enough nutrients in the soil to support all the leaves on a plant. Plants will also drop older leaves to "save" younger leaves if the plant remains too dry. Also if the pot and or soil does not drain well and root lose occurs, again the plant will sacrifice older leaves for the newer ones. Things to check - soil moisture, how well the pots drain, consider lightly feeding the plants if you believe nutrition might be lacking. Impatiens planted in the ground rarely need to be fed, in pots may be a concern. I hope you find this information useful.
Sincerely, Richard Hentschel
