Answer: Johnny jump ups are considered perennial so you can simply trim off the spent flower stems and they will flower again - all summer long. If you miss some of the flowers, the plants will set seed and self sow in the garden. I think this is why they are called that name, they tend to "jump up" in odd spots. This can be helpful because the original plants often bloom themselves into exhaustion and disappear.
Best wishes with your garden!
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