The present invention relates to a Spinacia oleracea L. seed designated 51-518 RZ, which exhibits a combination of traits including early bolting, a semi-erect plant habit, smooth mature leaves, field resistance against leaf spot diseases and resistance to downy mildew (Peronsopera farinosa f. sp. spinaciae) races Pfs 1 to 12 and Pfs 14. The present invention also relates to a Spinacia oleracea plant produced by growing the 51-518 RZ seed. The invention further relates to methods for producing the spinach cultivar, represented by spinach variety 51-518 RZ.
