Evening Primrose is a nice east plant to have in the garden, the flowers come out in the evening, hence the name, they are scented and flower for almost the whole summer.  it is a wildflower and can be seen in the fields everywhere. Once it is introduced into the garden you will never need to add another, Evening Primrose will seed itself around the original plant, sometimes a little further. However it is not invasive. Remember it is a biennial and once the seeds germinate the plant will not flower until the next year. I have several around the garden every year and it always seeds around the base of the plant. Any new plants that growe and are in the wrong place, I move them to a new position. Others I will pot on to give to others, or plant in another postion. 

At the end of the season the plant just needs to be removed and discarded once the flowering is over, however it will flower all the way until the first frosts begin. Next years plants will appear from september onwards, just look for the leaves on the plants growing around the  base of the mother plant