Hydrangeas, Demystified

Published On: August 17th, 2022


learn to identify your hydrangeas in wisconsin ftimg

Hydrangeas are an immensely popular group of plants. There are so many different types, each with its own specific care and maintenance considerations, that many gardeners feel confused and overwhelmed. Let’s take a look at the basics of this diverse Genus.

The most important element to understand: “New Wood” versus “Old Wood”

“New Wood” is stem growth produced during the current growing season. For Hydrangeas that bloom on new wood, pruning MUST be done before new growth begins or the current season’s flowers will be pruned off. Pruning is not necessary but can be done to shape or maintain size.

Blooms onNew Wood” = Prune Late Winter/Earliest Spring

“Old Wood” is stem growth produced during the previous growing season. These plants should be pruned – if necessary – immediately after blooming. Pruning after that would be removing next year’s blooming stems.

Blooms on “Old Wood” = Prune Immediately After Flowering

Identifying Your Hydrangeas

Climbing Hydrangea

Hydrangea anomala ssp. petiolaris

  • Hardy to Zone 4 (native to Siberia)
  • Partial to Full Shade
  • Climbs 30’-60’
  • Blooms early summer
  • Very slow to establish, and may take up to three to five years before it really begins to put on size. Once it finally takes off, though, it takes off! It climbs via aerial hold-fast roots that attach to the surface and can climb to 60’. Can be used to great effect to climb up a mature tree trunk, cover a stone wall, act as a groundcover, or climb on a structure. I have one that climbs my cement silo all the way to the top and is very impressive! Not suited to growing on a trellis or on a house with wood or vinyl siding.
  • Blooms on old wood (prune, if desired, immediately after blooming)

Oakleaf Hydrangea

Hydrangea quercifolia

  • Hardy to Zone 5
  • Partial Shade
  • Height 4’-6’ (depending on variety)
  • Blooms early to mid-summer
  • Best sited in a sheltered location.
  • Marginally bud hardy in our climate and therefore may not bloom reliably. The unusual structure and exceptional fall color earn it a place in the garden, even without flowers.
  • Blooms on old wood (prune, if desired, immediately after blooming)

Smooth Hydrangea

Hydrangea arborescens

  • a.k.a “Annabelle”
  • Hardy to Zone 3
  • Ideally sited in Partial Shade, but adaptable if provided ample moisture
  • Height 3’-5’
  • Blooms early summer through frost
  • This old-fashioned favorite has earned its place in the garden by being a hardy, reliable performer for generations. Flowers start out green/chartreuse, mature to creamy white, return to green, and finally age to beige. Leaving the beige flower heads over winter provides winter interest. If harvesting flowers for drying they should be cut and hung upside down just as they enter the second green stage to retain their color. ‘Annabelle’ has large, showy flowers on relatively weak stems, so the plants benefit from support to keep the stems upright. This can effectively be provided by growing Annabelle against a surface such as a fence or building, and then installing a lightweight wire support across the front for the stems to gracefully drape over.
  • Blooms on new wood (prune to ground in late winter or early spring )

Panicle Hydrangea

Hydrangea paniculata

  • Hardy to Zone 3
  • Full Sun to Light Shade
  • Height 3’-15’ (depending on variety)
  • Blooms mid/late summer through frost
  • This is the group that is truly supreme for our northern gardens! Absolutely hardy and a fantastic, reliable bloomer. Cone-shaped flower clusters are produced from summer through fall. Some varieties begin blooming as early as mid-July, and others start in August. Flowers start out white in most varieties and age from antique rose to strawberry red, depending on the variety. Plants range in height from 3’ to 15’, depending on the variety. A choice for every garden!
  • Blooms on new wood (prune, if desired, in the earliest spring). Never prune more than 1/3 of the total height of the plant.
how to prune your hydrangeas in wisconsin

Hydrangea paniculata should be pruned in very early spring before new growth begins. Remove the previous season’s flower clusters and prune shrub by as much as 1/3 to maintain compact form.

Bigleaf Hydrangea

Hydrangea macrophylla

  • a.k.a “Endless Summer”
  • Two Types: Mophead & Lacecap (different flower structures)
  • Hardy to Zone 6 / Zone 5
  • Partial Shade
  • Height 3’-5’
  • Blooms all summer under ideal conditions
  • Flower color is dependent on soil pH (acid=blue, alkaline=pink)
  • Older varieties bloom on old wood. Newer varieties bloom on old & new wood. Ideally, do not prune. Spring clean-up pruning can be done if necessary (cut out dead stems or portions or stems).  Size/shape pruning, if desired, should be done before August 1st.  To insure annual bloom it is best to site these in a sheltered location and provide winter protection.

Mountain Hydrangea

Hydrangea serrata

  • Hardy to Zone 6 / Zone 5
  • Partial Shade
  • Height 3’
  • Native to the high mountains of Japan, this relative newcomer has begun to take the place of the Bigleaf Hydrangeas, as it is a more reliable bloomer in our climate. This is a smaller, more compact plant with “lacecap” flower clusters of small florets in the center with a few larger, showy florets on the outside of each cluster, resembling a lace doily. Flower color varies from purple/blue to red/pink depending on soil pH.
  • Blooms on Old Wood. Prune, if desired, after blooming but before August 1st. Plan on providing winter protection.

Hydrangea “Tree”

hydrangea tree limelight find patio hydrangeas trees in flower

A Hydrangea “tree” is really that in name only. These Patio Trees are created by either grafting or training a Hydrangea shrub into a tree form, essentially a shrub atop a single stem. The stem itself will grow no taller but only increase in diameter. The top – shrub – piece will continue to grow and should be treated as you would treat the shrub if it weren’t on a standard.

Hydrangea paniculata is the only type of Hydrangea that can be used to create these “trees”, so pruning should be carried out in late winter. In order to keep the top growth from overwhelming the support stem, it will be necessary to prune heavily for at least the first few years.