Other contributors have said "How fast does a daffadil grow?" is the same question as "How fast does a flower grow?" If you believe that these are not asking the same thing and should be answered differently, click here
The fastest growing flowering plants are the annuals. Some of the more common annuals are:-Cosmos-Marigolds-blue flax-Sunflowers-Alyssum-Poppies-Snapdragons-Corn cocklesOne of my personal favorites...
Depends on the type of flower and even at that different breeds of the same species can grow they're roots at different rates. Also taking into consideration additives that has been added to the...