Happy New Year, koms1016. The wholesalers are experts at preparing the potting soil and the plant's environment (temperature, humidity, sunlight, etc) to produce the large blooms that you saw. Otherwise the shrubs may not catch your eye and they would not make a sale!

Many of the tweaks that they do involve supplying "appropriate" amounts of phosphorus. Phosphorus is good for roots and blooms.

Since potted plants tend to leach all these nutrients in time, determine how the current levels of nitrogen, phosphorus and pottasium are in the potting soil. Replenish any that are low. Add some chelated elements or trace elements with liquid seaweed or liquid fish and check the always important soil pH.

Some plant nurseries have kits that check nitrogen/phosphorus/potassium levels in the soil by mixing some soil + a special pill for each of those elements + water. You shake them well and observe what color the solution turns. One problem: this time of the year, the nurseries may have run out of stock of these kits so call before driving to the plant nursery.

Something else I have noticed... the first bloomage of the season for ES (in Spring) always looks better/larger/ (add more words ending in "er"). Blooms produced after that that do not match the ones produced in Spring. I have also noticed the same thing with my reblooming azaleas.

You did not say when the photo was taken but during this part of the year in the northern hemisphere, very few hydrangeas will bloom. Some shrubs in Florida may be able to eek a bloom or two in Nov/Dec if lucky but most hydrangeas just rest now before starting gangbusters again in Spring.

Luis

Why not plant them in the ground.?I have lots of
hydrangeas (however, no expert.) I'll bet that they'll
take off for you.
P.S... Luis is the expert...I always write to him for
hydrangea advice. I'm just puting my two cents in.

Margaret