They like an acidic soil - especially if you want the blue blooms. To supplement the fertilizer and add acid, you can use any of the following: aluminium sulphate (1/4 oz. per gal. of water), eggshells, coffee grounds, or ground up orange or grapefruit peels.
If you want pink blooms, use less acidic fertilizer. Some lime lightly applied may be OK. Be careful not to make the soil too alkaline, as that is not healthy for hydrangeas.
Blooms will start forming around the middle of June with the blooms out in early July. They will last until the end of summer. On a mature plant, the blooms will last some 4-6 weeks. They start greeny white and then turn pink or blue depending on the soil. Some plants and even some blooms may have both pink and blue on them. As the blooms mature, they turn to a more purple/lavender colour, then to lime green, and finally white & brown. Let them stay on the plant until next Spring.