Hydrangeas – Choose, Maintain, Enjoy!

Hydrangeas produce some of the biggest and most beautiful flowers in the garden and are a sign of summer here on the South Shore.  Hydrangeas are spectacular grown as single specimens, lined along a fence or foundation, or planted in a mixed shrub border.  With so many species and cultivars to choose from, the hydrangea is the perfect example of needing to (and being able to!) find the right plant for the right place.  They are so much easier to care for if you choose the right plant for your location, paying special attention to the amount of sun that the plant is going to receive and the size of the plant at maturity.  We’ve created this cheat sheet to help you select the right hydrangea and care for it to maximize its beauty and your enjoyment of it.  Here’s (almost!) everything you need to know about growing and caring for hydrangeas. We start with responses to some of the most frequently asked questions about hydrangeas and then provide details on the six hydrangea species most commonly cultivated and sold in New England. Make sure to scroll down to the bottom to our gallery of photos!

CHANGING COLORS

All hydrangeas undergo some color changes as their flowers age.  Many panicle-type hydrangeas (H. paniculata, aka Pee Gee or PG Hydrangeas) are prized for their large white flowers that change to pink in the fall.  Many of these actually start out a light chartreuse, mature to white, and age to a dark pink or even burgundy color. Smooth hydrangeas (H. arborescens, aka Annabelle Hydrangeas) can start out a pale chartreuse, mature to white or pink, and age to green or tan. Bigleaf-type hydrangeas (H. macrophylla) and mountain hydrangeas (H. serrata) with blue or pink blossoms can change from blue to purple to pink (or vice versa) based on the chemical makeup of the soil that they are planted in.  This is due to the acidity of the soil and the amount of aluminum in the soil.  Most hydrangeas with colored blooms will produce blue flowers in acidic soil and pink flowers in alkaline soil.

The traditional bright blue hydrangea that is so popular here on the South Shore stays that color because of New England’s naturally acidic soil.  We speculate that the hydrangeas planted beside our patio here at Kennedy’s (several different cultivars) are all pink because the lime leaching out of the bluestone pavers is making the soil that they are planted in more alkaline.

It is recommended that you do a soil test (either with a DIY kit that you can buy here at Kennedy’s, or by sending a sample to the Extension School at UMASS Amherst) before trying to change the acidity of your soil.  As a general rule of thumb, if your soil is turning your blue hydrangeas pink, you can reverse that trend by amending your soil with Espoma’s organic Soil Acidifier.  If you would prefer your hydrangeas to flower pink, make you soil more alkaline by adding Espoma’s organic Garden Lime.  You will need to be patient as these techniques will work gradually; the process can take two or more growing seasons to accomplish.  Read the labels carefully and/or check with our experts here at Kennedy’s for more specific details on the use of soil amendments to change the acidity of your soil.

As a rule of thumb, most blue hydrangeas can be changed to pink, and vice-versa.  The depth of the color is going to be similar in either color, so a pale blue hydrangea will transform to a pale pink, while a deep blue hydrangea will transform to a deep pink.  Most hydrangeas will pass through some version of purple on their way from blue to pink and vice versa.

FERTILIZING HYDRANGEAS

Don’t overfeed your hydrangeas.  Fertilize annually in late winter or very early spring with a slow-release fertilizer.  Avoid fast-release fertilizers with too much nitrogen as they will cause excessive foliage growth and diminished bloom.  While fertilizer itself won’t usually have an impact on the color of your blossoms, we recommend using Espoma’s organic Holly Tone fertilizer on your blue hydrangeas to feed and help keep the soil acidic.  For pink hydrangeas, use Espoma’s organic Plant Tone so as not to acidify your soil.  For white hydrangeas, either product can be used.

PROLIFIC FLOWERS (OR NOT)

We sometimes hear from our customers that their hydrangeas have great foliage, but no blooms. How can this be corrected?

1. Do not prune your bigleaf (macrophylla), mountain (serrata), oakleaf (quercifolia), or climbing (petiolaris) hydrangeas.  See the pruning paragraph for details.  (It is OK to prune PG (paniculata) and smooth (arborescens) hydrangeas without fear of losing flowers.)

2. Insulate the roots and stems of the hydrangea with leaves or salt marsh hay in late fall. This will protect them from cold winter temperatures that can kill the flower buds.

3. Plant hydrangeas in at least 3-4 hours of direct sun (preferably morning sun). If your hydrangea is getting less sun that that, you may want to move it to a sunnier spot. (But not too sunny/hot/dry!)

4. Fertilize with Espoma’s Triple Phosphate.  This will help promote flowering. (But only on stems that were able to set flower buds!)

5. Shock the root system. Take a shovel and push the blade straight down about 8-10″ away from the edge of the plant.  Do this all the way around the plant.  This may trick the plant into to thinking it is going to die and it feels the need to flower in a hurry so it can produce seeds.

6. If you have a plant that just won’t produce flowers, we recommend replacing it with a new variety.

PRUNING PRACTICES

The general rule for most hydrangeas when it comes to pruning is “DON’T!”  Most hydrangeas flower off the old wood.  This means the flowers will grow from the woody stems of last year’s growth.  If these stems are cut back, you cut back the number of flowers on the plant.  Wait until mid-June to clean up any stems that do not leaf out all of the way.  Cut them back just to where there is foliage.

Because most hydrangeas bloom on old wood, you can’t reduce the size of your hydrangea plant without losing flowers in the upcoming season.  If your hydrangea is too big for the area where it is planted, you are better off moving it to another location and planting a variety with a smaller growth habit in the original spot.

There are a few exceptions to the no pruning rule.  Paniculata hydrangeas like the ‘Pee Gees’ can be pruned in early spring (no later than the end of May) to control the size or give it a better shape.  Arborescens hydrangeas like the ‘Annabelles’ can be pruned in early spring also.  Some people give their arborescens hydrangeas a hard prune in late winter to revitalize the plant and to encourage shorter and stronger stems that won’t droop under the heavy weight of the flowers when they are in full bloom.

WATERING REQUIREMENTS

Most hydrangeas require moist but well-drained soil.  Their roots are shallow and dry out quickly in hot, dry weather, leading to drooping foliage and blossoms.  Most hydrangeas prefer to be planted where they receive afternoon shade to protect them against the hottest temperatures of the day.  As with most plants, an occasional deep watering when needed is better than a daily light watering.  Three inches of bark mulch helps regulate soil temperature and retain water.  Make sure to pull the mulch away from the base of the plant.  On particularly hot days, your hydrangea will benefit from a misting of the entire plant.  This cools the plant and reduces the amount of water it loses through transpiration. Oakleaf hydrangeas are the only hydrangea that can tolerate dry to average soil.

Hydrangea macrophylla

BIGLEAF HYDRANGEA
AKA MOPHEAD HYDRANGEA, AKA LACECAP HYDRANGEA

Flower Shape & Size: Mopheads have large, pom-pom-shaped flowers.  Lacecaps have flat, lacy flowers.  The flowers may reach as much as 8″ wide on mature plants.

Flower Color & Time: Flowers can be white or can range from blue to purple to pink.  Shades can range from pale to deep.  These hydrangeas flower beginning in late June.

Light Requirements: Part shade.  They prefer morning sun with afternoon shade, and need 3-4 hours of sun for the best blossoms.

Hardiness Zone: Most macrophyllas are hardy to zone 5.

Plant Size: 6-8’ tall and wide, with some new cultivars bred to be more compact.

Prunable? Blooms on old wood and should not be pruned.  Winter damaged stems may be cut out in early spring.  Wait until plant has leafed out in June before cutting back the tips of dead stems.  Minor pruning if needed immediately after flowering.

Other:  Protect in winter (mulch for roots, leave for stems) to maximize blossoms.

Native to:  Japan (coast)

Popular macrophylla cultivars – Mopheads: Pia/Pink Elf, Penny Mac, Mini Penny, Enchantress, Endless Summer reblooming series (including Original, Bloomstruck, and Summer Crush), Forever and Ever reblooming series, Cityline reblooming series, Let’s Dance reblooming series, Onyx series

Popular macrophylla cultivars – Lacecaps: Variegata, Lace Cap Improved, Wedding Gown, Light O Day, Lady in Red, Mariesii/Blue Wave, Endless Summer Twist-N-Shout, Let’s Dance reblooming series

Hydrangea serrata

MOUNTAIN HYDRANGEA

Flower Shape & Size: Lacecaps with flat, lacy flowers.

Flower Color & Time: Flowers range from blue to purple to pink.  Shades can range from pale to deep.  These hydrangeas flower beginning in late June.

Light Requirements: Partial shade.

Hardiness Zone: Most serratas are hardy to zone 6.

Plant Size: 2-4’ tall and wide.

Prunable? Blooms on old wood and should not be pruned.  Winter damaged stems may be cut out in early spring.  Minor pruning if needed immediately after flowering.

Other: Very similar to Hydrangea macrophylla and considered by some to be a subspecies.  Flower buds are typically more cold-tolerant than the macrophyllas, but they will still benefit from winter protection (mulch for roots, leave for stems) to maximize blossoms.

Native to: Japan (mountains)

Popular serrata cultivars: Blue Billow, Bluebird, Tuff Stuff series

Hydrangea quercifolia

OAKLEAF HYDRANGEA

Flower Shape & Size:  Large, cone-shaped flowers.

Flower Color & Time: Creamy white flowers beginning in late June/early July normally age to pink in fall.

Light Requirements:  Full sun to partial shade.

Hardiness Zone:  Most quercifolias are hardy to zone 5.

Plant Size:  Upright, irregular shrub gowing to 4-8’ tall and wide.

Prunable?  Blooms on old wood and should not be pruned.  Winter damaged stems may be pruned in early spring.  Minor pruning if needed immediately after flowering.

Other: Large, oak leaf shaped foliage has a nice burgundy color in fall.    Dramatic peeling bark provides winter interest.  Drought-tolerant compared to other hydrangeas; dry to average soil is OK.  Flower buds are typically more cold-tolerant than the macrophyllas, but they will still benefit from winter protection (mulch for roots, leave for stems) to maximize blossoms.

Native to:  Southeastern United States

Popular quercifolia cultivars: Snow Queen, Snowflake, Ruby Slippers, Pee Wee, Gatsby series

 

Hydrangea anomala petiolaris

CLIMBING HYDRANGEA

Flower Shape & Size: Fragrant white flowers in flat-topped, lacecap clusters (to 8” wide).

Flower Color & Time: Pretty white flowers beginning in late May.  Flower heads dry to reddish-brown.

Light Requirements:  Part shade to full shade.

Hardiness Zone: Most petiolarises are hardy to zone 4.

Plant Size:  Can be grown as a groundcover or shrub, but usually used as a vine grown in shade.  Climbs easily on masonry or up a tree.  Can reach up to 50’.

Prunable?  Blooms on old wood and should not be pruned.  Winter damaged stems may be pruned in early spring.  Minor pruning if needed immediately after flowering, or as needed to direct growth.  If the climbing hydrangea vine is badly overgrown, reduce the size gradually by staggering the pruning over a span of two or three years.  Old, neglected vines can be cut to the ground.  You won’t have any blooms the coming season, but the rejuvenated plant should come back better than ever the following year.

Other:  Nice glossy, dark green foliage when grown in shade.  Useful for covering walls.  Exfoliating bark on mature stems is reddish brown and attractive in winter.

Native to: Japan, Korea, China

Popular petiolaris cultivars: Miranda, Moonlight Magic

Of note: Similar to Hydrangea anomala petiolaris (aka Climbing Hydrangea) is a vine from a different genus called Schizophragma hydrangeoides or Japanese Hydrangea Vine. Popular cultivars of Japanese Hydrangea Vine include Moonlight and Rose Sensation.

Hydrangea paniculata 

PANICLE HYDRANGEA
AKA PEE GEE/PG HYDRANGEA

Flower Shape & Size: Paniculata hydrangeas have large, cone-shaped flowers.

Flower Color & Time:  Flowers are usually white or pale lime green.  They flower beginning in July and the flowers on many varieties turn pink or red in the fall.  The flowers are great for cut fresh or dried flowers.

Light Requirements: Full sun to partial shade.

Hardiness Zone:  Most paniculatas are hardy to zone 3.

Plant Size:  Paniculata hydrangeas are large plants that may reach up to 8-15’ in height, 6-12’ in spread.  Dwarf cultivars are also available.

Prunable? Blooms on new wood and can be pruned in late winter/early spring.  Cut back by ¼ to ½ to remove old flowers and encourage new growth.  Larger cultivars can be pruned to keep them at about 8’ tall and wide.

Other:  Easy to grow and very cold tolerant.  This plant is available in shrub form (multiple trunks) or in tree form (single trunk).

Native to:  China, Japan

Popular paniculata cultivars: Grandiflora, Tardiva, Limelight, Little Lime, Quick Fire, Little Quick Fire, Bobo, Phantom, Moonrock, Pink Diamond, Pinky Winky, Vanilla Strawberry

Hydrangea arborescens

SMOOTH HYDRANGEA
AKA ANNABELLE HYDRANGEA

Flower Shape & Size: In the species plant, flowers bloom in flattened clusters, 2-6”across.  A few large sterile flowers usually appear at the cluster margins (usually not enough for a quality lacecap effect).  Cultivars feature much larger flowers than the species, producing huge, symmetrical, rounded heads up to 8-12″ across.

Flower Color & Time:  White flowers from May to July.

Light Requirements: Part shade.

Hardiness Zone: Most arborescens are hardy to zone 3.

Plant Size: 3-6’ in height and spread.

Prunable? Blooms on new wood and can be pruned in late winter/early spring.  Plants may be pruned back close to the ground in late winter to revitalize and to encourage vigorous stem growth and best form.  If not pruned back, any weakened and/or damaged stems should be removed in early spring.

Other:

Native to:  Eastern United States

Popular arborescens cultivars: Annabelle, Lime Rickey, Incrediball series, Invincibelle series (including Mini Mauvette and Limetta)