For me it is Salvia coccinea. It starts blooming about a month after the young plants are put in about mid May and continues to bloom until frost. It is highly attractive to hummingbirds too and will self sow in coming years. If you do a search you will discover that quite a few seed companies offer it - usually Lady in Red and Coral Nymph.

We manage to kill every seed or seedling my children bring home from school. They get knocked over, they dry out, or they steam to death if you put a baggie over them. Or they never come up. So give them seeds that can go in the ground, that don't have to be started in pots.

Zinnias, sunflowers, a mini-pumpkin, cosmos. I love snow seeds - you throw them on the snow over the garden bed- larkspur, poppy. Send them with a little picture of the seedling as well as the flower.