Marigolds from seed, although they take awhile to bloom, are well worth it since that is often the ONLY way to get truly unusual plants. Also, they establish themselves much better.
Garden center plants are usually treated with chemicals which limit their growth in the packs. Plants in packs tend to get leggy, and the chemicals allow them to maintain a neat, compact look. This, however, is bad once they are planted since it also limits their growth in the garden!
Marigolds you grow yourself do not have this treatment unless you apply it. Therefore, they are free to grow to their full glory, which is wonderful in the garden. And if you start them inside, and they get long and leggy, that's good. Those ugly ducklings will be beautiful once they get used to being outside and start to bloom all up and down that long stem (that main stem which will probably fall over and lay on the ground the minute you plant it out there!) Just leave it on the ground, the part hitting the ground will grow roots and the part facing up will grow many blooming offshoots!
Garden center marigolds usually grow about 6 inches high, while those planted inside from seed usually hit a foot of bloom-filled growth. Those growing from seeds planted outside end up at about 9 in.
This kind of plant doesn't need any. NO work here! But if you really want to, you can put down A LITTLE Milorganite, or compost. Tilling in some compost actually seems to work better for marigolds.
Go light on any kind of fertilizer with marigolds. If the soil is too rich, they don't bother to put out many blooms. Sometimes overfertilized soil will cause them to stop blooming altogether. But you'll get lots of leaves!
Avoiding Gardening Work
The Preen Page
Compost and other Basics
The Obligatory Rose Page