In the Northern Hemisphere (the northern half of the earth), the vernal equinox marks the beginning of Spring on March 19, 20, or 21.
(the vernal equinox; marks; the beginning of Spring; T:on March 19, 20, or 21; L:In the Northern Hemisphere)
the vernal equinox
marks
the beginning of Spring T:on March 19, 20, or 21 L:In the Northern Hemisphere