Testing Soil Quality by Growing Radishes. If your radishes matured and you harvested a healthy crop, your garden soil is good to go. If your radishes fail to produce a vegetable root but grew a lush, healthy top that means that the soil lacks phosphorous and potassium. Yellow, unhealthy-looking (chlorotic) leaves tell you that iron, sulfur, nitrogen and other trace minerals are lacking in your soil. You will have to amend for these deficiencies as needed.
Testing Soil Quality by Growing Radishes : MrBrownThumb