Answer: They may have suggested marigolds for several reasons: the seeds are easy to find and inexpensive, the germination rate is generally excellent and very fast, they are easy to start from seed and they grow quickly so that results should become apparent fairly soon. It also adapts well to pot culture. Garden marigolds (Tagetes) are decended from a wild Mexican species so in fact they are originally from a warmer climate.
If you would prefer a foliage plant with a more tropical "look" rather than a common flowering plant, you might try coleus which originates from the islands of the South Pacific. It too is a reasonable choice in keeping with the points above although it is a bit more difficult to germinate because it requires a warm soil temperature and is a bit slower growing.
I hope her experiment goes well.
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