... with very important work cautions: you might want to thoroughly organize everything, so that you avoid unwanted paint spots all over the place including the t-shirt. Don't forget to place paper inside the t-shirt so the back doesn't get printed too. Choose the plants.
Take one, put it on a piece of paper, start applying paint with the brush, then place it on the t-shirt. Cover the painted plant with another piece of paper and press lightly. Remove the paper and the plant. Wash the brush and repeat as many times you want, changing the plants and colors.
Correct the design by adding color drops with a fine brush - I used golden tint for the final touch.
Here it is:
Have lots of fun creating your own :-)