Here's how I did this:
-Reach the second area (high street)
-Go back to the garden and take the flask to the store in the high street, just drop it on the floor
-Go back to the garden and take the trowel, have the man chase you
-Reach the store and run past the flask, and then drop the trowel
-The man should pick the flask up and take it back to the garden, soon after returning for the trowel which the shopkeeper has put out for sale