One time we asked a champion radish farmer in Laguna what tip he would tell a neophyte so that his radish will yield big roots.
Very important, he said, is not to fertilize the radish plants with nitrogen when they are already starting to develop their main root. That means don’t apply urea or ammonium sulphate when they are already 20 to 25 days old.
Why? We asked. The roots will not develop well because the applied nitrogen will promote instead the production of more leaves rather than enhancing root growth.
Of course, he said, it is also important to plant the right variety. His favorite, according to him, is Mt. Data. In 45 days from seeding, the roots can already be harvested.