In the summer, folks come home from work at their jobs and hang out in their yards - they mow the lawn or weed the garden or have barbecues. I don't cook much, but just before dark I like to have a couple of friends over. We get out the beach chairs, face them toward the garden and get ready for my favorite summer evening entertainment. We watch my evening primroses open. It's positively thrilling. They’re yellow evening primroses – oenotherea flava. During the day, the flower buds are tightly closed, forming little cones, but each evening the buds burst and four beautiful pale yellow petals unfurl in about sixty seconds. It's like watching Disney time-lapse photography. The flowers then stay open all night, but are closed up again before noon the next day. Why are the flowers opening at night and how do they know when it's getting dark?