Monday, May 17, 2010

How and when to prune hydrangea macrophylla in zone 5b Ontario?

in the fall after the bloom season

How and when to prune hydrangea macrophylla in zone 5b Ontario?
"Pruning can be accomplished at two different times. Late summer is more desirable, since most hortensia types flower only from the end buds of upright or lateral shoots produced during late summer and fall of the previous season. Prune as soon as the flowers have faded and strong shoots are developing from the lower parts of the stems and crown. Remove at the base some of the weaker shoots that are both old and new. Always try to keep several stems of old productive wood, with a sufficient number of stout new stems that will flower the following season. Early spring pruning (March), although acceptable, will result in the sacrificing of bloom for that growing season.

Pruning this species too late in the fall (after September) is harmful. New growth, both vegetative and reproductive, will not develop proper maturity. Hortensia is a good seashore shrub; flowering is more profuse in an open, sunny location. This, however, increases its vulnerability to bud killing. Winter protection of the plant should be initiated in December to preserve buds for next year's flowering. Tie the shoots together and wrap with burlap. If left unprotected, delay any Spring pruning until the buds swell in order to determine which wood needs to be removed, and then cut back to below the point of injury."
Reply:I live right at the border of Zones 5b and 6a. I have grown quite a few cultivars of Hydrangea macrophylla, and I believe minimal pruning results in the best plants. I like the the look of the "old" flowers, so I leave them on the plants through the winter. In March I remove just the old bloom, not much of the stem with it.

My experience would indicate that the second year the plant is in the ground is the toughest to get flowers. In the second season about 50% bloomed, but once I get past that I've had 100% of the plants flower (Most of them have been in the ground 8-9 years now).

As a general rule plants in this species flower on the stems from the previous year. Some of the newer cultivars also flower from the new growth (those are the ones with names like 'All Summer Beauty' or Endless Summer')

Good Luck!
Reply:Cut down to the ground 1/3 of theOLDEST canes (So say 1/9 of all the canes but the oldest ones)

Here in BC we prune in Jan but that could be too late for you

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