Vert
Vert is the heraldic tincture for green. It is one of the five main colours. In engravings Vert is shown by diagonal lines running from the upper left to the lower right as you look at the shield. The word is French for green and has been used in English heraldry since the early 1500s.
Green is less common than red or blue in medieval arms and more common in modern ones. French heralds no longer say vert: they use sinople, a word that once meant a shade of red. In English blazon a green hill under the shield is often called a mount vert, a common kind of compartment.
Choose Vert by name in the color picker of the coat of arms maker. It works for a whole field, an oak tree or a laurel wreath from the Plants group on the Charges tab. Put a metal such as Or or Argent on top so it reads well, following the rule of tincture.