I just planted 3 varieties of blackberries in my garden. Apache, Arapahoe
and Rosenburgh. The only one that is producing any berries is Rosenbergh,
but they seem too sour. They get full sun, are in soil lightened with peat
and a little sand, and get adequate water. The plants are beautiful, as are
the berries. Is there some soil amendment I can add to sweeten the berries?