The present invention relates to a Spinacia oleracea seed designated 51-348 RZ, which exhibits a combination of traits slow to medium growing, smooth leaves, dark green leaves, medium to late bolting, and resistance to downy mildew (P. farinosa f. sp. spinaciae) races Pfs1 to Pfs15 and intermediate resistance to Pfs16. The present invention also relates to a Spinacia oleracea plant produced by growing the 51-348 RZ seed. The invention further relates to methods for producing the spinach cultivar, represented by spinach variety 51-348 RZ.
