Description CULTURE: Because of tap root, it is advisable to avoid starting carrots in flats for transplanting. Plant seeds after soil reaches 55° F. SOIL: Carrots do best in rich, noncompacted soil high in phosphorus and potassium and moderate levels of nitrogen. SEED PRODUCTION: Store best roots for replanting following year or leave in the garden and mulch heavily. Flowering tops are quite large so leave at least 2′ spacing between carrots.