Single Versus Double
B. Rosie Lerner, Extension Consumer Horticulture
Specialist, Department of Horticulture & Landscape Architecture,
Why are some flowers referred to as "single", and others
and still others as "semi-double"?
The answer lies in the petal count. A single flower has a single
count of petals, such a this single rose bloom. Different species
plants vary what is considered a single number of petals. Five
most common single flower petal count among the various horticultural
species, but some species have 3, others have 4.
A double flower has some multiple of single petal count. Semi-double
would be a multiple number between single and double count.
How these terms are exactly defined may vary depending on the
species. The American Rose Society has established the following
definitions for petal count on roses.
SINGLE - 4 to 8 petals
SEMI-DOUBLE - 9 to 16 petals
DOUBLE - 17 to 25 petals
FULL - 26 to 40 petals
VERY FULL - more than 40 petals
The terms 'fully double' and 'very double' are often seen in
publications but are not official, nor have petal counts been
to these terms.