True to their name, plum tomatoes are tomatoes about the size of a plum. They are a fleshier tomato with less pulp than other types. Plum tomatoes hold their shape well when canned, and are easier to slice because of their high ratio of flesh to pulp. Plum tomatoes often boil down faster than other varieties. Growing conditions for plum tomatoes are similar to other tomato varieties, but germination for some heirloom varieties may be more difficult. Start with more than the usual number of seeds to increase your chance of success.
Amish paste tomatoes originated with the Amish, a group of traditional Christians that practice varying degrees of simple living that range from absolute renunciation of modern life to accepting some basic modern conveniences. This variety of plum tomato has very thick walls and fewer seeds than many other tomatoes. It is good both for cooking and canning, and is considered an heirloom variety that can be difficult to germinate in some areas. Research by Purdue University on Amish paste tomatoes showed that they had a lower germination rate (21 percent) in northern areas and thus would require higher seeding densities. With adequate seeding, Amish paste should grow anyplace in North America where other tomatoes grow, and mature 80 to 100 days after planting.
Costoluto Genovese are uneven and lobed, but because of their structure are considered a plum tomato. Plum tomatoes have a higher ratio of flesh to pulp and often have fewer seeds, making them ideal for pastes and sauces. Because of their irregular shape, these tomatoes are not as good for canning or slicing. Contoluto Genovese mature 70 to 80 days after planting.
Romas are evenly sized tomatoes that are good for stewing, cooking, slicing or canning. Because of their high percentage of flesh over juice, Romas are often the preferred tomato for tomato paste. Once the skins are blanched and removed, Romas can be simmered until they are reduced to a smooth tomato paste. Because of their regular, round shape, the skins of Romas easily slip off after blanching. Romas mature 70 to 80 days after planting.
Another popular plum tomato is the opalka. An heirloom variety, opalka are solid-fleshed tomatoes the size of larger plums. They are very dry with few seeds, making them an ideal tomato for tomato-paste based dishes. Opalkas mature 80 to 90 days after planting.