1. Lots of sun.
2. Keep deadheading. Break off the old blooms. You can leave on a few if you want some seeds, but don't leave the majority.
3. If your veggies are doing well the marigolds should be doing well, too. They are hardy little plants. They attract bees and pollinators which you want in your garden. Are they getting enough sun and water? You might try a little fertilizer.
4. It's also still early in the year and in my state, Nebraska, it's been cold. My tomatoes are just starting to bloom and the entire garden looks short, weak and spindly. I only have one marigold blooming. In fact, I've planted marigold seeds 3 times this spring. The first 2 times they didn't germinate and I've NEVER had marigold seeds where NONE of them germinated.
5. During this part of the year I've noticed marigolds spend more time growing up and out, less time blooming. By August you'll have bushes of blooms (probably). Store-bought marigolds should be ahead of the game a litte, but if it's not hot and wet enough, they just kind of sit around.
Heidi

Ya didnt tell people that when you dead head marigolds those are seeds. . You need to leave the dead heads out to dry well before putting in a bag or they wont cure properly. This year I will be mixing different marigolds together. Did you know there is a white marigold Also a Pretty White Zinnia that fits perfectly with zinnia's :O)