If you plan to grow your tomatoes in containers vs garden and you want large plants, you should start your seeds late Feb. or early March. If you want tomato plants about 15-18" tall and maybe starting to blossom, ones that have been uppotted to a pot about the size of a gallon milk jug, the seeding date is around the first day of spring. For the smaller size plants like the ones in the "1 Cup" size pot, target your seeding for early April or about 3 weeks from St Pat’s day. The seeding of peppers should be done in early to mid March. Some peppers take a while to germinate. I’ve waited on habaneros for 2-3 weeks. But if kept warm enough most peppers pop in about a week.
From mid April to the end of April or early May start cabbage, broccoli, cauliflwer, kale, kohlrabi. Germination temperature for these is 70*F and germinate in a couple of days. Cinco de Mayo (May 5) and Mother's Day are other holiday markers. At this time you can start seeding the cucumbers, squash, pumpkins, and melons. These like a germination temperature a little warmer at 75-80*F. Again these germinate quickly. But for best results I would wait until the garden soil is warm ( end of May/early June) and sow these directly into the garden.
Now for flowers. Here I don’t have extensive experience because we grow large quantities of purchased plug seedlings. But we do seed some zinnias and sometimes alyssum, and many of the marigolds. All of these sprout readily and we seed them in that second half of April time period, maybe a little earlier for marigolds if you want buds. I would figure 8 weeks from seed to first bud on marigolds ( French type/small flower). African type marigolds take longer. (tall and large flower). Zinnias can also be directly sown into the garden.
Tomorrow's topic - Transplanting to the outdoors.