As my herb garden has grown, I've had a harder time identifying the plants. Some, like Sage "Berggarten", Chives, or Lemon Balm are quite easy to ID. I can even tell the difference between the "Grosso" and "Silver Edge" lavenders.
I have the hardest time with oregano and marjoram. It's no wonder since they come from the same family (origanum) and look (and smell!) a lot alike. Now that they're in bloom though, I thought I might have some luck in figuring out which is which. Google is great. I googled "marjoram or oregano" and came across this nifty article which did all the homework for me. It's a nicely written piece that goes indepth about these herbs.
In the end I learned that most oregano flowers are pinkish-purple, while they're white on marjoram. I quickly ran out to the garden, and sure enough...I can tell a difference!! Apparently the leaves have differences too, but I couldn't see them with my lay-gardener's eye. When I felt the leaves, I could tell a difference. The marjoram leaf feels smoother, kind of waxier. The oregano, while not fuzzy, was definitely coarser.