The Hanging Basket Garden in High Park was just one of my areas of care during my days as a gardener for the City of Toronto. The baskets were grown in the City Greenhouses first, then my colleagues and I would spend a day arranging them outside when there was no risk of frost.
About 100 or so baskets of mixed annual flowers were on display in this area. Periodically, I'd spend about 2 days going through them all, cleaning out dead growth, dead-heading flowers to stimulate more blooms or checking to see if the drip lines were working properly. Each basket was connected to several drip lines set up on a timer for a water feed.
Even though the automatic watering system existed, during the dry periods of our Toronto summers the baskets had to be watered manually. With hanging baskets and most potted annual displays, the roots are tightly packed into their pots and are actively competing for water. As it flows in the basket or pot, the water soaks the outer surface of the soil and works it's way down the sides of the container.
If the water is not fed for a long enough period, the very center of the root clump will tend to dry out resulting in the death of your flowers! Water as often as needed (every 2 to 3 days), but at least once a week during drought periods, give that container a great soaking by filling a bucket with water and submersing the container in the bucket. Letting it sit until no bubbles come out from the soil is the best way to ensure even water distribution throughout the root clump.
If you are watering with a wand connected to the hose (recommended for delicate annual plantings), water until you see it flowing out the drip holes of the container, stop for a minute or so, then repeat 1 or 2 more times. The Japanese have a rule of thumb for bonsai plants (annuals are no different), water 3 times, once for the pot, once for the soil and finally once for the roots (plus the occasional dunk in the bucket).
Follow those simple suggestions and your baskets/pots should last till the first frost in fall. Anticipate that frost!!!... trim all the growth back before it hits, store the plants indoors in a cool place keeping soil moist and you can have that same planting arrangement for next spring! (feed with a bit of slow-release fertilizer in spring)