Broccoli seeds can be sown directly into the garden but perform best transplanted. Start broccoli seeds indoors 6 weeks before the last frost in your area. Follow the seed depth and spacing guidelines indicated below. Once all danger of frost has passed, seedlings should be hardened off before planting in their growing location. Seedlings should be transplanted according to the plant and row spacing directions below. Regularly monitor your plants and ensure that the soil remains moist, but not soggy while they establish themselves in their new environment.