The plastic pots get hot in my summers so I try to give them some shade. Shrubs can also quickly start growing rots in circles in those small pots so I have to keep an eye on the roots coming out of the bottom holes. If growing a hydrangea, keep this in mind, especially if the hydrangea grows vigorously. Not sure if you plan to overwinter them, but I would use another type of pot in that case. Mopheads can be around 6 feet or less. Those won't "fit" in 2g pot for long but for a while may be ok. Did the flyer say the type of hydrangea that you are talking about?

They can't overwinter outdoors in Toronto in pots of any kine. You might be able to overwinter the in the pots in a cool garage if you have space.

True. I did not mean to say that about potting them outside.. I would not try to overwinter them in those rinky dinky plastic pots in a garage in extremely cold or warm zones anywhere. Last time I bought a plant in those plastic pots, they were almost paper thin to the touch. Felt like it was a kind of cheap and thin plastic on the top edges (probably had been recycled too many times). Hee hee hee. ;o) Just use a better kind of material and put them in a shed or garage where they can be protected from the cold... heated garages, etc.