This week our Garden Guru has received multiple questions about when and how to prune Hydrangeas. Below is a little primer!
Hydrangea microphylla, both mophead and lacecaps, should be pruned in late summer/early fall right after the flowers have faded. The buds for next year’s blossoms are formed in October. If a hydrangea produces no flowers, it is probable that it was pruned too late in the year.
Prune stems back to the first or second pair of fat buds below the finished flower. This can be as little as 4”. It is not necessary to prune farther back unless you want to reduce the height of the shrub. Remove canes that are thinner than a pencil to encourage larger blooms on remaining canes. Remove all small, twiggy growth and dead wood.
September/October is also the time of year to treat the soil around Hydrangeas to change or deepen flower color. Use Hydrangea Blue or Aluminum sulfate to make flowers blue or purple (acid). Treat the soil with Agricultural Lime to make flowers pink (alkaline). If your Hydrangea is white, the color cannot be modified. The harder wooded Hydrangeas, H. arborescens, H. aspera and H. paniculata, are pruned in late winter. Their flowers are formed on new, spring wood.