The tricky prepositions. . . "in my garden"
在我花园里有很多果树 is the most accurate.

上 means on, on top of. If you use 上 people will think your garden has a roof, and those fruit trees are planted on the roof.

Source: http://baike.baidu.com/view/256231.htm

站 invokes the image of standing on one's feet in a stiff, rigid, upright manner. unless you want to emphasize the upright, honest and steadfast manner of some pine or poplar trees, most garden trees are everything but stiff. 

Source : http://baike.baidu.com/view/259393.htm