Grow Heirloom Tomatoes - Plant San Marzano Tomato Seeds. San Marzano Tomatoes proudly maintains characteristics of the perfect paste, puree or canning tomato. San Marzano matures in clusters, holds well on the vine and in storage, is crack resistant, and processes well due to its solid nature. For these reasons, San Marzano Tomatoes remain Italy's top choice as the perfect canning tomato.