Answer: Your dahlias will bloom better if you deadhead, so yes that is a good thing to do and also customary. If you leave the faded bloom on the plant long enough to set seed, the plant's energy will go to seed formation rather than more blooming. If you do manage to save viable seed, the seedlings will not be the same as the parent plant. For these reasons, most gardeners would increase their dahlias by dividing the tubers. This yields new plants that are the same as the original. Since you need to dig and store the tubers for the winter (if you want to keep the plants from year to year) the dividing is relatively easy to do.
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