Tomato plants are naturally self pollinating and a general characteristic of self-pollinating plants is that they become genetically homozygous after many generations. Since they do not naturally out cross very often, seeds of a tomato will produce plants resembling the parents. Growing heirloom tomatoes was a natural practice long before it was given a name.
Early cultivars did not change much because of this property and were kept in a family or community for long periods of time. Heirloom tomato cultivars dating back over a hundred years are still grown today.
Most heirloom varieties are unique in size, shape or color. Some are black, dark purple, or red with black shoulders, many are green, some have green stripes or are rainbow colored or shaped like peppers. Our course there are orange and yellow heirloom tomatoes and everything in between. Some are cherry sized and some are over 1 kilogram (2 pounds).
Because heirloom tomatoes haven’t been modified by plant breeders, they don’t usually have much disease resistance. However, many diseases can essentiallybe prevented or delayed by mulching the soil surface to prevent disease spores in the soil splashing up and infecting the young tomato plants. Mulching plus fungicidal sprays mean that heirloom tomatoes can usually be successfully grown in all but very hot humid areas.
Since heirloom tomato varieties have become popular in the past few years there have been liberties taken with the use of this term for commercial purposes. If you want to grow heirloom tomatoes that have been passed down for several generations look for Family Heirloom Tomato seeds.