How and When to Prune Hydrangeas

In the 1960s, gardening author, Sima Eliovson wrote, "It is a distinctive feature of most southern African homes to boast a line of hydrangeas along the shady south wall". Whilst the decades have moved on, hydrangeas are still used throughout in shady gardens across the country.

In the southern hemisphere november is the time when hydrangeas burst into a blush of mauve, white and pink flowers. However, it is late July when the seeds of a successful flowering season are sown. The big question is Should you prune a hydrangea in July or in late January after the flowering season is over?”

Top Johannesburg gardening expert, Andrew Balfour says, As the flowers of the common garden hydrangea (Hydrangea macrophylla) are borne in summer on the old wood, pruning should theoretically be carried out directly after flowering in late January. Theoretically you could be removing the old canes and be dead-heading the previous years stems which only bore a single flower.

In practice however, the pruning of hydrangeas in South Africa is most successfully carried out in late winter when the leaves have dropped from the dormant plants”, he says. If July is the time to prune hydrangeas, how do you do it? If you look at a hydrangea at this time of the year, you will see that there are different types of wood, according to age, on the bush”, says Balfour.

There are young slender growths of the previous summer reaching up from the base of the plant. At the end of this stem there is a large bud. This bud, in the next growing season, will produce a short shoot and then a flower”, he adds.

There are also older shoots two seasons old. At the end of these stems there is a dead flower (if not removed by dead heading), while a short distance down the stem will be found a cluster of large buds usually four to six in number. These, if left, will each produce a flower the following summer. All that is needed is to prune the stem back to just above the cluster of buds”, he says.

Older, heavier stems of two or more seasons will also be found, carrying several dead flower heads, and these should be pruned back hard to the base of the plant to stimulate new, vigorous growth the following season”, he adds.

If the entire shrub is pruned back hard to the base, or if the stems are pruned to half their length, then it is quite possible that the flowering buds would be removed resulting in a poor show the following summer”, concludes Balfour.