Tomato seedlings should be transplanted first when their first set of true leaves appear. The true leaves are the second set of leaves that emerge, following the initial cotyledons (seed leaves) which feed the plant until it can start photosynthesis properly. Typically, this happens about 2 to 3 weeks after sowing seeds. At this stage, seedlings can be moved from small seed starting trays into larger containers or pots, ideally placing the stem deeper to encourage more root growth. As the plants grow, they may need to be transplanted again into even larger pots or finally into the ground. It's also important to wait to transplant tomato plants outdoors until after the last frost date and when soil temperatures are consistently warm, above about 16°C (60°F), to avoid cold stress. In summary:
- First transplant: When the first set of true leaves appear (about 2-3 weeks after sowing).
- Subsequent transplanting: As plants outgrow containers, usually when roots become dense or plants reach about three times the height of their container.
- Final transplant outdoors: After last frost date and when soil temperature is warm enough, usually mid to late spring depending on climate.
This approach helps build a strong root system and avoids transplant shock while ensuring healthy growth.
