Singles have 5 petals, semidoubles have 6-9, and doubles have 10+ petals.

Awesome! Thank you so much. I hadn't realized it that simple.

What might be confusing is that many varieties are listed as "single-semidouble." This means that a given plant may have both single and semidouble blooms. Some may have more semidouble than others; this can prove disappointing when you've bought a variety from a photo that showed mostly semidoubles and your plant has mostly singles. Speaking from experience.

Also, a semidouble may only have a tiny extra petal in the center but it's still a semidouble. Other semidoubles appear nearly double.

Diana

Thanks for clearing up the single-semi-double conundrum. I have several flowers that I would call singe but have that funny little extra flippy petal in the center so I guess officially they are semidoubles. Even though its like 5 1/2 petals! Thank you so much!!! Hope you are having healthy AVs!

Liz