The most productive of all the commercially grown blackberries is the Thornless Evergreen, or Black Diamond. This variety is very popular with growers because of it's ease in growing and larger yields. The Thornless Evergreen is very vigorous, disease resistant and productive, yielding 6-10 tons per acre. The fruit is black, one and half inches long, firm and sweet. The seeds are quite large, being one of it's least desirable qualities. One of the problems with Thornless Evergreens is that the season is very late, which makes it more difficult to harvest due to weather and labor problems.