Poor size marigold plants?
 

I have been planting the Lady (First Lay) series of marigolds for over 20
years and every year they have grown 20 - 24 inches tall and approximately
12 to 16 inches wide. Last year the plants grew less than 12 inches tall
and about 8 - 10 inches wide. This year they also look very small about 8
inches tall and not looking to grow any taller. I raise my plants indoors
from fresh purchased seed every year and they are normally 6 inches tall and
harden off with one blosom each when I plant them the 1st week in June after
the frost here in northeastern PA. They get a nice constant supply of water
without over watering as they are under a slight overhang. They currently
get 7 hours of sun as they have over the last 20 years. I use Peters Blosom
Booster for fertilization as I have done so over the last 20 years. I added
compost this year and none last year so that doesn't seem to contribute to
the small size.


Any suggestions as to how I can get my marigolds to grow to the 20 -24 inch
height as I have done so in the past?