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When to Prune Hydrangeas
Hillary T
When to Prune Hydrangeas

Hydrangeas flower either on old wood or new wood. That's hydrangea lingo for if they flower on stems from last year (the old wood) or stems from this year (the new wood, also called new growth).

Pruning time depends on if the hydrangea flowers on old wood or new wood. If it flowers on old wold, prune it after it flowers; if it flowers on new wood, pruning is more flexible and you can prune after it flowers and before it flowers.

Here's a list of hydrangeas grouped by flowering season that tells you when it's okay to prune.

 

Winter

Hydrangeas that bloom on new wood can be pruned when dormant in the cold months. They can be pruned before they flower.

Hydrangea arborescens (smooth hydrangea)

Hydrangea paniculata (panice hydrangea)

 

Spring

Similar circumstances to winter. Those same two hydrangeas flower on on new wood (i.e. new growth of the season) and pruning in spring still means that you're pruning them before they flower.

Hydrangea arborescens (smooth hydrangea)

Hydrangea paniculata (panicle hydrangea)

However, if the shrub has already broken bud and branches have begun to grow, pruning at this phase will likely delay flowering by a few weeks. This delay is not a big deal, but if you're expecting it to flower during it's typical time-frame and are planning a party, please keep this in mind. Maybe it's best to hold off on pruning a year? Or prune less?

 

Summer

All hydrangeas can be pruned in the summer.

These 3 hydrangeas bloom on old wood, i.e., from buds that are set in late summer or autumn the year prior.

Hydrangea macrophylla (bigleaf hydrangea)

Hydrangea quercifolia (oakleaf hydrangea)

Hydrangea serrata (mountain hydranea)

If you want to enjoy next year's flowers on those hydrangea species, the only time to prune them is right after they flower and with enough time for them to set flower buds for next year. In zones 7, 8 and warmer, that means don't prune those above 3 species after August 1st. 

Ahem, there is an exception, of course. See the "When to Prune Remontant Hydrangeas" section below.

These hydrangeas flower on new wood, so they can be pruned in the summer after they are done flowering. However, I don't prune them after August 1st either. I pretty much don't prune any plant after August 1st because I want them to have plenty of time to regrow before they need to harden off for winter.

Hydrangea arborescens (smooth hydrangea)

Hydrangea paniculata (panicle hydrangea)

 

Fall

Similar again to pruning in winter. Hydrangeas that bloom on new wood can be pruned when dormant in the cold months - that theoretically includes in the fall because you're pruning them before they flower the next year and you'll still get spring flowers.

Hydrangea arborescens (smooth hydrangea)

Hydrangea paniculata (panice hydrangea)

I personally don't prune hydrangeas or much of anything in the fall for several reasons:

  • Too much else going on with fall planting, leaf raking, and all the holidays.
  • I love the dried stems and flower heads of everything from panicle hydrangeas to the structural seed heads of perennials. I let them be until late winter when they start looking too raggedy for me to bear. 
  • For those hydrangeas that flower on old wood, the pruning window is very tight. Hydrangeas that flower on new wood have a much more lenient pruning time-frame that spans winter, spring, and summer.
  • Plus, there are horticultural theories as to why pruning in the fall is a bad idea for the health of the plant. This is especially important for tender plants or plants with low chill hour requirements because pruning in the fall can  stimulate new growth and that's the opposite of what one wants - one wants their plants to go dormant as winter approaches.

venn diagram showing when to prune hydrangeas

 

When to Prune Remontant Hydrangeas

Taking what we learned above and what we learned in our blog post "What Are Remontant and Free Flowering Hydrangeas?" here are rules of thumbs:

Hydrangea arborescens (smooth hydrangea) is remontant, so prune this species right after spring flowering and you'll get a second flush of flowers in late summer or fall. Don't prune it back hard unless it's too big for the area - basically just deadhead or prune off a node or two.

For remontant Hydrangea macrophylla (bigleaf hydrangea) cultivars, keep in mind that the first spring flush is from old wood. If you prune the shrubs in fall, winter, or spring, you are pruning off your spring flower bouquet. However, you will still get that second flush in the autumn.

picture of a remontant hydrangea in context of when to prune it

When to prune a remontant BloomStruck hydrangea? Right after it flowers and it will bloom again that fall. Or, you can prune it it winter/spring and you may miss spring flowers, but you'll certainly get that flush of remontant fall flowers.

 

In zones 7 warmer, to maximize flower power of these remontant types, prune them in mid-summer right after they flower and before August 1st, just like the non-remontant types. This still gives them time to grow and flower from that new wood!

Truth is, if you've planted your hydrangea in the right place and it has plenty of room to grow, you don't really need to prune your hydrangea. 

Consider not pruning: read our blog post Do I Have to Prune My Hydrangeas? to learn why not pruning is a fine option.

 

May your pruners always be sharp,

Hillary & Mike 

Tags:pruning

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