If you're desperate to get this one out of the way quickly, the orchids will respawn with a different colour every time.
With this in mind, if you exit the screens in order by using the exits up, left, left, down, there should be an orchid to your left (either a Tulip-looking flower or a green blob measuring about nine pixels by four!) upon entering the fifth screen, with minimal activity around it. I recommend this one as there is minimal chance of getting knocked about by the bad guys before you make the pickup.
Simply turn on infinite lives, camp, and collect the orchids until you have all five.
Edited to remove spelling mistakes!