Question: Three years ago we planted one small Mexican primrose (Oenothera) in our garden. Three years later, our garden is over-run with this plant. How do we get rid of this invasive plant?

Answer: The most effective means of getting rid of this invasive plant (and many other weeds) is to cut back any and all green parts of the plants. Every time the roots send up shoots, cut them down to ground level. Eventually the roots will run out of energy and will die. If you allow the shoots to develop leaves you'll defeat the purpose because leaves will convert sunlight into energy for the roots. But you will eventually starve out the roots with constant and continual removal of shoots as soon as they appear.