By Alyson Prokop, Manager of Adult Education
August, 2025
There’s something about heirloom tomatoes that makes gardeners go absolutely plum wild.
‘Sart Roloise,’ growing in the Climate Garden, will develop a slight blush when ripe. Slice it open to reveal vibrant yellow. Photo by Megan Stouffer/New England Botanic Garden
Maybe it’s their weird and wonderful shapes, or the way their colors flirt with every shade of red, yellow, green, and even purple. Maybe it’s their flavor, sun-warmed and bursting with personality—nothing like their store-bought cousins. Whatever the reason, growing heirloom tomatoes is a love story that begins in the soil and ends in sauce. Or salad. Or, if you’re like my neighbor down the street, just eaten whole over the sink with a sprinkle of salt and a gleam in your eye.
But the real romance? That’s in the seeds.
Heirloom tomatoes are open-pollinated varieties, meaning they pass down traits reliably and deliciously. Saving seeds from your best tomatoes not only ensures you’ll enjoy that perfect flavor again next year, but it also helps preserve biodiversity and gives you ultimate bragging rights at the next garden potluck: “Oh, this variety? It’s a fifth generation ‘Mortgage Lifter’ tomato that dates back to the 1940s. No big deal.”
If you want to get started with tomato seed saving, the process is simple. Pick your healthiest, tastiest fruit, scoop out the seeds, and ferment them in a mason jar with just enough water to cover the seeds. Let them sit in the tomato water for a few days. That slimy coating around tomato seeds isn’t just gross, it contains chemicals that prevent germination and can carry plant diseases. Fermentation mimics what happens when a tomato rots naturally. It breaks down the gel, kills off many pathogens, and separates out the duds. Within two to four days of fermentation, you’ll notice a layer of mold forming on the surface. That’s your signal the process is working.
Yes, it will smell weird. Yes, that’s part of the charm.
At this point, strain and remove the ‘goo’—the liquid and pulp—and any floating seeds. The good, viable seeds will sink to the bottom, while the floaters are usually non-viable. Rinse your seeds thoroughly and then spread them in a single layer to dry completely. They should look clean, tan, and papery when ready. An old window screen, ceramic plate, or sheet of newspaper all work just fine.
Store your seeds somewhere cool and dry (like a paper bag) and make sure to label them! This way next spring when you’re ready to grow your tomato dynasty, you’ll know what you are growing.
Most gardeners sow tomato seeds indoors 6 to 8 weeks before their region’s last expected frost date. For New England, that usually means late March through early April. Start them in small trays or pots with a light seed-starting mix, keep them warm (70-75°F / 21-25°C), and give them plenty of light. Once seedlings develop true leaves, thin them out and pot them up. They’ll be ready to harden off outdoors once nighttime temperatures stay above 53°F (10°C) and the soil has warmed.
Don’t forget the support your tomatoes need along the way—both emotionally and structurally. A good trellis helps tomatoes stand tall, keeps fruits off the ground (less rot, more hot tomato action), and opens up space for you to grow even more plants. Here at the Garden and at places like Seed Savers Exchange, we love the simple twine-and-stake method—just jute twine and metal or wooden stakes. No fancy equipment needed, just a little garden elbow grease and a game of cat’s cradle with string.
Need seeds? Make sure to research trusted sources. Or ask a neighbor who seems to have more tomatoes than blood in their veins. They probably have a few secrets worth saving. In the end, heirloom tomatoes remind us of something simple: great things grow when you save what matters, pass it on, and always—always—leave room for one more tomato plant.
Interested in learning more about plants and gardening? Join our community of plant-loving learners with a class or workshop at the Garden.
About the Author
Alyson Prokop is NEBG’s Manager of Adult Education by day and a botanical adventurer at heart. She believes that plants aren’t just background scenery—they’re teachers, companions, and a source of endless inspiration. Whether designing puzzles about carnivorous plants, brewing hand-blended teas, or leading educational programs, her work always circles back to the living green world. Some people chase trends; Alyson chases roots, leaves, and petals, and collects seeds (once growing 88 different varieties of tomatoes in her market garden!). Her mission is to help others rediscover that spark of connection with plants—because life is richer when you let a little chlorophyll into your story.