I have approximately 25 dahlia's planted, I have noticed that 5 of them are not growing as rapidly as the others. While most are two feet tall, the other are only about 12 inches. I have not even pinched them yet. Two of these are in prime location in my yard for maximum sun.
We have not had good weather which is unusual here-we haven't had sun for two solid weeks and I did plant later than usual. It also has been cooler than normal.
I usually plant in March but couldn't plant until the end of April.