Seed catalogues are full of terminology which isn’t always well-explained. Here is a quick glossary of relevant terms and characteristics to pay attention to when choosing your varieties, including OP vs Hybrid, Determinate vs Indeterminate, Treated vs Untreated, and Heirloom vs Heritage seeds.
Open Pollinated vs Hybrid
Open Pollinated (OP): So long as plants of an OP variety are kept isolated from different plants with which they can be cross-pollinated, they will produce seed that is "true to type." In other words, the plants in the following generation will be of the same variety as the parent plants. OP plants are pollinated by wind, birds, bees and other insects. If you want to save your own seed*, choose OP varieties and make sure you give them enough distance from similar varieties in your garden so they don’t cross-pollinate!
Hybrid (F1): These seeds are the first generation offspring of two distinctly different and genetically pure parent plants. Seed saved from F1 plants will not express the same traits as its parent. New varieties are often created through hybridization in the hopes of combining specific desirable traits expressed by the parents, such as increased productivity, ease of harvest, shape, colour, or disease resistance. These seeds are almost always impossible for seed-savers to reproduce because they're made by crossing proprietary parent varieties that are corporate trade secrets.
*For more detailed information on successful seed saving, check out our handbook How To Save Your Own Seeds!
Determinate vs Indeterminate Tomatoes
Determinate (AKA ‘Bush’) varieties generally have a heavy fruit set over a relatively short period of time, then stop producing fruit. When fruit sets on the terminal bud, the plants stop growing, and all the fruit tends to ripen around the same time, after which the plants die back. The plants tend to be more compact, so can be good choices for container gardens or when you have space limitations. Determinate varieties are also a great choice for tomatoes that you want to harvest lots of all at once for canning! Pay special attention to the Days to Maturity when choosing determinate varieties so you can spread out your harvest by planting some early, mid and late season types.
Indeterminate (AKA ‘Vining’) plants produce fruit continuously over the course of the season, generally continuing to produce leaves, flowers and fruit simultaneously right through to frost. These plants tend to grow larger, developing longer vines that require more support. Indeterminate varieties are great choices for snacking on or slicing into salads bit by bit over many weeks. Many (though not all) heirloom varieties are indeterminate.
Treated vs Untreated Seed
Treated Seeds have been coated with a chemical agent to help protect against common pathogens. Often a fungicide has been applied to help keep seeds and seedlings from rotting or damping off in cool, damp soil. Seeds may also have been treated with insecticides to kill off insects that tend to feed on seeds or young plants.
Untreated Seeds have not had any synthetic chemicals applied to them. Certified Organic growers are required to use untreated seed. Some untreated seeds may come out of the package with a silvery or white coating – this is merely a colouring agent applied to make them easier to see when sowing.
Heritage & Heirloom Seeds
These terms get used interchangeably and actually have more to do with ownership than age. To be considered heritage/heirloom, seeds must be public domain (aka “the people’s seeds”) and Open Pollinated. They have generally been grown for at least 1 generation, though many have been around for much longer. These seeds play an incredibly important role in preserving our food’s genetic biodiversity and regional adaptations.