Tomato Seed Saving (Harvest of the Month for Educators Activity)

For this hands-on activity adapted from Shelburne Farms, students will estimate how many seeds are in a tomato and then learn how to save tomato seeds through fermentation. You will need cherry tomatoes, plates, and child-safe knives (or you can do the cutting for students). For seed saving you will need small cups, a fine mesh strainer, a sink, paper towels for drying seeds, and small envelopes to store the seeds once dry.

Hold up a cherry tomato and ask students for their ideas on what is inside. (Seeds.) Ask how many seeds they think are inside the tomato and whether they think each cherry tomato will have the same number of seeds. (Explain that the number of seeds can vary between plants.) Tell students that they will explore how many seeds a plant produces and how this helps seeds survive.

Give each student or pair of students a cherry tomato. Ask them to guess how many seeds are inside and record their guesses on a whiteboard or flipchart. Then give each pair a paper plate and a child-safe knife. Have them carefully cut the tomato in half and count the seeds. If working in pairs, they can count together. Ask them to compare the number of seeds they found with their original guess. Record the results and discuss what they noticed. Ask students why they think each tomato has so many seeds? How many tomato plants could they potentially grow from their cherry tomato? (The same number of plants as seeds.) Ask students if they notice that each seed is surrounded by a protective layer of gel. Tell them that this coating helps to protect the seeds. 

If you want to continue the activity, students can also save the seeds to share with others or plant themselves. Tell students to scoop the seeds and the jelly-like pulp into a small cup. Add about 1–2 tablespoons of water to the cup and gently stir. Students will need to let the seeds ferment by leaving the cup in a safe place at room temperature for about 2–3 days. The mixture may develop bubbles or a thin layer on top. This is normal. Pour the mixture through a fine strainer and rinse the seeds with water until most of the tomato pulp is gone. Spread the seeds in a single layer on a paper towel or plate and let them dry completely for about a week in a warm, dry place. Once the seeds are completely dry, store the seeds in a labeled paper envelope in a cool, dry place until you are ready to plant them in the spring. As an additional activity, students can create seed packets for their seeds with growing instructions, and even start a classroom “seed library”.