I predict frustration as a result of your endeavors unless you're willing to give up the annual marigold as it completes its growth cycle & dies each year. May I suggest you try dwarf snapdragon, dwarf geranium, any number of Coleus with small leaves - Impatiens repens is excellent as are several of the doubles, artillery fern (snip & grow - excellent as a clump), or calibrachoa. I have several of these plants that are 5 years old or older. They develop quickly & make neat conversation pieces, companion plants or excellent palm-sized bonsai after about 3 years.

Geranium and snapdragon young starts:
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Photos are 4 years old & I still have the plants. These were taken at the beginning of the second growth cycle.

Al