Zinnias a flower I used to plant often, as did my Mother. Wonder why I got out of the habit? Funny, as I think back so did she. Zinnias are annuals, though they do come in both seeds and plants; most often you see them in seed. Perhaps that's why we both changed our habits. Annuals require more work then perineals do. Seeds though cheaper require more work then seedlings/plants. We planted seeds back in the day. There are many varieties, many sizes, many colors and once they grow, quite easy to care for.
These make wonderful flower beds whether you choose a mix as above or all one color and all one variety. There are small shorter single varieties that make lovely edges, the larger double and giant flowers are great to cut. Zinnias will continue to flower after you cut and bring in doors. In addition, they will continue to bloom if you dead head regularly. They'll branch and be more bushy if you pinch them back. They attract Butterflies and Hummingbirds to you yard, as well as beneficial insects. Indoor bouquets do best if you cut the flower blossom before it's fully opened.
I live in planting zone 5, which means seeds could be sowed indoors as early as late in the month of March; or sowed outdoors in late April. Burpee suggest planting in full sun after the threat of frost is mostly past. Plant seeds 12 inches apart with 1/4 inch soil covering them. Water frequently keeping them moist during seedling stage. Generally you'll see your seedlings within 7-10 days, at which time you're suppose to thin them to 18-24 inches apart. I can't say I ever did that, and doubt Mom did either. Who wants to pull out a plant that's trying to grow? Not me.
I've not thought about these flowers in some time, and need to review my yard to see if there's a place I might like to plant them again. I do love to attract Butterflies.
And Happy Birthday Chuck, my oldest brother. Shall I pick a bunch of flowers for you?