Answer: I am so sorry about your nasturtiums! Based on your description I am not certain what has happened. The black granules could be the excrement of a caterpillar or other pest (although the most common pest on nasturtium is more likely to be aphids clustered at the growing tips -- this plant is generally quite pest resistant), and the sudden overnight wilting could have been caused by a wilt disease possobly something like tomato spotted wilt which can even cause black specks. There is also the outside possibility of accidental herbicide contact or some other unusual occurrence such as a vole eating the roots. Your local county extension may be aware of any localized problems people are having with their nasturtiums in your area this year, too.
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