They are healthy plants, but they definitely do not put out a lot of blooms. -- Virginia Olienechak, Penfield. On some types of hydrangeas, the flowers we see this summer are from buds they set last fall (old wood). So if you prune them in late fall or early spring, or a cold winter kills the buds, you get no flowers. For these types, I recommend you prune immediately after flowering (if you need to) so the plant still has a chance to develop flower buds for next year. Oakleaf (Hydrangea quercifolia) fits into this category, as do the mop-head and lace-cap (H. macrophylla) types (usually pink or blue).
http://www.cleveland.com/insideout/index.ssf/2011/06/pick_right_time_of_year_to_pru.html
I prune my 'Annabelles' in early spring before growth starts. I cut out weak stems and cut back strong stems by about two-thirds. This allows the plant to have fewer but bigger blossoms on strong stems, as opposed to many small wimpy ones that dive face first into the mud in the first heavy rain.
http://www.cleveland.com/insideout/index.ssf/2011/06/pick_right_time_of_year_to_pru.html
To encourage blue blooms in alkaline soils, add aluminum sulfate, composted oak leaves, pine needles or coffee grounds. To encourage pink blooms in acidic soil, add wood ashes, lime or fertilizers with high levels of phosphorus (a ratio of 25-10-10 is best) to prevent aluminum from entering the plant’s system.
http://www.endlesssummerblooms.com/design-and-grow/planting-and-care
When it's pruning time, you could remove the canes that are at angle of less than 45 degrees to the ground level. Also, remove all old canes from the center to give way to stronger vertical canes growing from the center.
http://www.almanac.com/plant/hydrangea
Therefore, on these special hydrangeas, if the bloom buds are killed by frost or pruned off at the wrong time, they will regenerate the bloom bud and bloom as usual. ('Endless Summer' is just such a hydrangea.) To the right is a picture of a hydrangea that has this trait.
http://www.hydrangeashydrangeas.com/pruning.html
PRUNING MADE EASY(Hopefully). FIRST, it's important to know that mophead hydrangeas do not have to be pruned back-ever-unless they are very old. Removing dead stems is the only pruning that must be done for the health of the plant, and these can be removed at any time. Dead blooms can also be removed at any time.
http://www.hydrangeashydrangeas.com/pruning.html
How to Prune Hydrangeas: Endless Summer hydrangeas require very little pruning day-to-day, so you are able to simply enjoy the beautiful plants. These perennial hydrangeas bloom on growth from the current year as well as previous years, which allows for the re-blooming throughout the summer.
http://www.endlesssummerblooms.com/design-and-grow/planting-and-care
Planting Hydrangeas. Endless Summer® Hydrangeas is a collection of Hydrangea macrophylla perennial shrubs that have the unique ability to re-bloom throughout the spring and summer months, giving more color and visual appeal to your garden for a longer period of time.
http://www.endlesssummerblooms.com/design-and-grow/planting-and-care
First, you need to know what type of hydrangea you have. For mophead, lacecaps, and oaklead varieties, the best time to prune is actually in the summer before August. They form their buds on old wood in Aug/Sept/Fall for the following season's bloom.
http://www.almanac.com/plant/hydrangea
Make sure that the crown of the plant – where the base of the stems meets the soil – is even with the ground level. If the hydrangea is placed too high, it can easily dry out. If the crown is placed too low when planting, it can cause hydrangeas not to bloom and potentially rot.
http://www.endlesssummerblooms.com/design-and-grow/planting-and-care
when is the right time to prune hydrangeas
The right time to prune hydrangeas is immediately after flowering.