C. F. Keil and Franz Delitzsch on Leviticus 25:5

Lev 25:5

“That which has fallen out (been shaken out) of thy harvest (i.e., the corn which had grown from the grains of the previous harvest that had fallen out) thou shalt not reap, and the grapes of thine uncut thou shalt not gather.” נזיר, the Nazarite, who let his hair grow freely without cutting it (Num 6:5), is used figuratively, both here and in Lev 25:11, to denote a vine not pruned, since by being left to put forth all its productive power it was consecrated to the Lord. The Roman poets employ a similar figure, and speak of the viridis coma of the vine (Tibull. i. 7, 34; Propert. ii. 15, 12).