Things were simpler decades ago when hydrangeas, Hydrangea macrophylla, were either white or not white. Those that were not white were mostly pink locally because of the alkaline soil of the Santa Clara Valley. Blue hydrangeas where seen where the soil is acidic in the Santa Cruz Mountains, or where the soil was amended to be acidic. (Acidity causes flowers to be blue. Alkalinity causes flowers to be pink.)

Now there are more than five hundred cultivars of hydrangea! Although bloom color is really determined by pH, many cultivars make better blue shades, and many others make better pink shades. Purple and red have been added to the mix, while white has become less common. After getting pruned low while dormant through winter, most hydrangeas grow about three or four feet tall and broad through summer. Some can get twice as large, while many stay low and compact.

Most hydrangeas have ‘mophead’ blooms, which are large, round ‘panicles’ (clusters) of smaller sterile flowers. ‘Lacecap’ blooms are flat topped panicles with narrow borders of the same small sterile flowers surrounding lacy centers of minute fertile flowers. Hydrangeas bloom from early spring late into autumn.