Question
My sun impatients have grown to about 36". They are now falling over from the weight of their stems. Should I cut them back, if so, how much?

Answer
You can cut impatiens stems back to a few inches tall. Let 2-3 sets of leaves remain on the stems. It will take 3-4 weeks from cutting back until flowering. Keep the sun impatiens in a reasonable amount of direct sun (depending on your location). It will speed up flowering, if you add 5-10-10 or similar at time of cutting back, unless you have fertilized recently.