Pot marigolds are a wildflower that grow in poor soil and can even grow in partial shade. However, for optimal results and the most blooms, use rich and well-draining garden soil and place your winter beds in full sun.
As with any form of winter gardening, pot marigolds should be placed in a raised bed. There are two advantages to this. First, the soil will be a few degrees warmer if raised off of the ground a few inches. Second, raised beds drain more efficiently, ensuring less risk of root rot.
While a frost is rare in milder climates, anything is possible. You can protect your growing marigolds from winter frost by covering the plants with a sheet at sunset. Always be sure to remove the sheet promptly at sunrise so that the plants can warm up and dry off from any residual dew.
If you want your marigolds to last through the winter into spring, continually dead head the blooms. This will trigger more blooms to form and prevent the marigold from going to seed. It is always wise to let some of the plants go to seed, so that you will have some seeds to harvest and replant next winter.