I have grown, from what is resembles on the internet, an african marigold. The problem is that its stem grows too tall, 1-1.3 m (3-4 feet) with only 2-3 blooms on top and the bottom is dried up. I have seen the same marigolds with dwarf size 0.3-0.6 m (1-2 feet) with green foliage and lots of bloom. What is wrong here?
As I'm sure you realize, all one can do at this point is speculate. But in general there are two common reasons plants grow tall but have unusually few flowers. One is insufficient sun. The other is seriously excessive nitrogen. I am putting my bet on the sun shortage. Insufficient sun will also tend to make a plant shed its least productive, often lowest, leaves.
There are different varieties of African Marigolds; my first seed catalogue to hand lists four varieties, with heights [12", 18", 30", 48"] so your observed height is not out of the ordinary. The thing to realize is that different heights are offered for a reason. If you are planting up a flower bed to be viewed from a pathway you might plant all four varieties, the shortest in the front closest to the viewer, and the tallest at the back furthest from the viewer. If this bed is an island to be viewed on both or all sides (circle) then the tallest go on the inside and the shortest used as edging.
The result is of course that it does not matter if the tallest lose leaves at the bottom, their bottoms will be covered up by the next tallest from the point of view of the stroller by the next tallest. Just as well too, since we don't want to view uncovered bottoms. Very unsightly.
So the solution for the OP is to make sure they have seed for the variety that provides the most suitable height for the location.