How Do I Prevent Radish Roots From Growing Out Of Soil And Not Forming A Radish?
This even happens when planted in potting soil.
Certified GKH Gardening Expert
This, usually, indicates a lack of phosphorus in the soil. It could also indicate that there is too much nitrogen, which is common with most potting soils.
This can be offset by adding more phosphorus, and potassium, as long as the soil pH is not neutral or alkaline already.
This article will offer more information: https://www.gardeningknowhow.com/edible/vegetables/radish/radish-does-not-form-bulbs.htm