Marigolds make great container plants. They fill out and get nice and bushy, while blooming almost non-stop. Remember to match the mature plant size to the container size. The T. patula French marigolds can be grown in smaller containers due to their smaller plant size. One French marigold will fill a 6-inch pot. French marigolds can be planted with vegetables in the same container. Combining various cultivars requires more attention to the water and fertilizer needs of the plants. French marigolds will thrive in larger containers such as wine barrels, urns, or redwood planters. One consistent rule for all container gardens is to ensure that water drains from the soil. Use containers with holes on the bottom or sides.
Both T. tenuifolia, signet, and T. erecta, African or American marigolds can brighten any patio with bold color grown in containers. Signet marigolds require a 6 to 10 inch container while the African or American needs more space and soil. Use a 12 to 15 inch diameter container at least 18 inches deep for the mid height range T. erecta.
Source: National Garden Bureau.