Answer: Rhododendrons rarely require pruning, so I would not think your new plants need any.
Mums are generally left alone in the fall, then trimmed back very short to about an inch high in the early spring being careful not to damage the new growth coming up from teh ground. At that time you would usually also divide the plants and replant the more vigorous outer portions to grow on for bloom in the fall. These new plants will need to be pinched regularly to develop thick dense branching with ample buds. Pinch out the growing tips every other week or so until mid July. After that, stop pinching and allow them to grow. Enjoy!
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