Experts and BHG readers answer.
Dahlias not blooming
Dahlias are not actually bulbs; they are tuberous roots which easily can dry out in storage over the winter. That might have been what happened to yours. Did you moisten them before storage and during the winter? The ones that came up but did not bloom are probably still good, if they still have a fleshy part to the roots. This winter, check them and sprinkle water on them if they appear to be drying out. Vermiculite, perlite, dry sand and peat moss or wood shavings are good storage mediums.