Hydrangeas come in many different types. This includes Hydrangea Macrophylla, Bigleaf or French, Panicle (Smooth), Oakleaf, and Climbing varieties. All of these have distinct characteristics and are grown in different regions all around the world. The most common type is the Bigleaf which are known for their big puffy formation of flowers. These are also known as mophead, lacecap, and mountain varieties. The mountain hydrangea is similar to the lacecap, but has smaller blooms and are very cold hardy. Most hydrangeas can be grown in Hardiness Zones 3 through 7.
This is an example of a pannicle hydrangea. It has a large grouping of small flowers formed on a long stem that gives it a long cone shaped appearance. Smooth or panicle hydrangeas are known to be cold hardy to temperatures as low as -30F.
This hydrangea is capable of changing colors based on the composition of the soil type. When soil is more acidic, below a pH of 5.5, the flowers look like this photo, blue in color. If the soil is more neutral, between 5.5 to 6.5 pH, the flowers turn a gentle purple, or lilac. In basic soil, above 6.5 pH, the flowers turn pink. This type of hydrangea can be grown in hardiness zones 6 to 9. They can withstand -10F temps.
This type of hydrangea also belongs in the macrophylla family. It is named for the texture due to the flattened corymbs with center flowers mimicking lace surrounded by sepals that are the typical flowers hydrangeas are known for. The flower buds form in the summer and autumn. There is a chill time of 1,000 to 1,200 required in order for buds to able to open the following spring. H. macrophylla blooms on new wood and should not be pruned until after it finishes blooming for the season.