9 Frequent Hydrangea Questions Answered

Why aren’t my macrophylla hydrangeas blooming?

Macrophylla hydrangeas of the lacecap varieties have large, sterile florets surrounding smaller flowers, giving them an airy, lacey appearance.

Macrophylla hydrangeas of the lacecap varieties have large, sterile florets surrounding smaller flowers, giving them an airy, lacey appearance.

1. Too much shade - limb up trees for high shade or move plant to more sun

2. Late freeze killed buds — You could select hardy varieties such as “Endless Summer”, “Penny Mac”, “Preziosa”, “Mme Emile Mouillere”, “All Summer Beauty”, “Dooley”, but if you have a late freeze when the plants have leafed out you will find most hydrangeas will lose their main (terminal) buds regardless of how winter hardy they are.

3. Incorrect pruning — for most mophead and lace cap hydrangeas you should prune right after blooming but not any later than late July to avoid cutting off next year’s buds. Hydrangea paniculata and Hydrangea arborescens bloom on new wood and should be pruned in late winter.

How can I make my mophead hydrangeas turn blue/pink/purple?

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1. To turn Hydrangea macrophylla blue use a fertilizer low in phosphorus and high in potassium, or the organic approach,  Espoma HollyTone as directed or 1 tablespoon aluminum sulfate per gallon of water before buds set in July and then again in August. The more acidic your soil, the more likely your hydrangeas will be blue (pH of 5.5 or below).  Avoid high phosphorous fertilizers (see #2).

2. To turn Hydrangea macrophylla pink or red spread powdered lime (2 cups per plant and water in during early spring and again in autumn).  Seek a pH of 6.5 or higher.  Aluminum is in ready supply in acidic soils, but phosphorous locks up aluminum;  you could consider applying super phosphate or bone meal.

3. To turn Hydrangea macrophylla purple you need skill and luck and the right variety. “Merritt’s Beauty”, “Ami Pasquieri”, or “Mathilda Gutges” are good varieties to try.  The soil pH needs to right in the middle of the scale between turning hydrangeas pink or blue (about 6.0)

4. You won’t turn “Annabelles” (or any other mophead that is white) blue or pink, but she does respond well to an application of HollyTone in making blooms a brighter white.

Keep in mind that you won’t achieve color change overnight. It is a slow process.  Color can be affected by location. A concrete walk nearby can help turn hydrangeas pink. Hydrangeas under pine trees are apt to be blue from the acidic breakdown of pine needles.

What companion plants will complement my hydrangeas?

Oakleaf:  Magnolia, Red Maple, and Sourwood (red fall foliage to echo the color); Front with a medium growing blue hosta and a layer of purple shamrock; also Autumn Fern, Astilbe, Aruncus (Goatsbeard), and Virginia Sweetspire look good with Oakleafs.  ‘Cleopatra’ Camellia sasanqua shows off well in the fall as the foliage of Oakleafs turn maroon. White impatiens look fabulous underneath.

Blue Hydrangea macrophylla also looks stunning with orange flowers, like these crocosmia.

Blue Hydrangea macrophylla also looks stunning with orange flowers, like these crocosmia.

Macrophylla: Under plant with clematis to climb up through, lower growing ferns, Forget-me-nots, Astilbe, European Ginger, Pulmonaria (Lungwort), Exima ‘Luxuriant’ Bleeding Heart, Lenten rose, Iris cristata (bloom while hydrangeas are dormant), Epimedium, Sarcococca, and Bergenia.  Nearby plantings might include Rhododendron, Daphne odora, Cephalotaxus ‘Harringtoniana’, Camellia sasanqua, Pieris japonica, Cimicifiiga, and Thalictrurn.

Arborescens (Annabelle):  Upright Cephalotaxus, spiky & tall Astilbe, Maidenhair Fem, Lady Fern, Shaggy Shield Fern, Kalimeris, and variegated hosta all look terrific.

What is the bloom sequence of the various species (in Greensboro, NC)?

Oakleaf blooms late May and early June

Annabelles bloom in early June

Macrophylla begin blooming in early to mid June and some varieties bloom a week or two later

Paniculata bloom in July and August

How do I prune hydrangeas?

Anomala:  After blooming but probably would never need this.

Oakleaf:  After blooming to shape only as it probably doesn't need any pruning.

Hydrangea arborescens 'Annabelle'

Hydrangea arborescens 'Annabelle'

Arborescens : Late February prune the old wood not more than 24 inches from the ground for stiffer stems to support somewhat smaller blooms. I've found that if the old wood is not pruned so hard it is more supportive of the blooms.

Macrophylla : You should prune after blooming to shape it but, as a general rule, not later than late July.  Cut the old, woody stems that are finger thick or that are misshapen all the way to the ground.  In spring if you are unsure if winter damage occurred, wait until it leafs out to remove old stems.  This kind of pruning helps rejuvenate the plant.

Also pinch out the damaged, dead top buds to encourage the side buds to flower.  Flower buds are formed at the terminal (end) of the stem and, if not killed by cold, provide the show. However, additional flower buds are sometimes present, often along the entire length of the stem, just not as large as the terminal bud.

Paniculata:   PeeGee and Tardivas should be pruned back in late February to within 1 to 2 inches of where last year’s growth started.

What diseases and pests affect hydrangeas?

Relatively pest free, but the most likely problems are botrytis, bacterial leaf spot, powdery mildew, spider mites, slugs and aphids. Hydrangea aspera is loved by Japanese beetles. 

Leaf purpling of hydrangeas is a common complaint, and is most commonly caused by one of two issues: lack of phosphorus (the middle number in fertilizer analysis) or a fungus called cercospora.

If it's phosphorus deficiency, which can happen when the soil pH is lowered too much in search of the perfect blue bloom, back off on soil acidifiers first and see if the problem resolves the following year. If not, use a high P or 'blossom booster' fertilizer to bring up phosphorus levels.

Cercospora infection will show as purple spots, rather than an overall purple cast to the leaf. Cultural controls include providing good air circulation through pruning or good planting location, and making sure the hydrangea is not in too much sun. Cercospora seems to be worse on shrubs located in more sun than they need.

What do hydrangeas need to thrive?

Hydrangea quercifolia4normanack
Oakleaf hydrangea (H. quercifolia)

1. Macrophyllas prefer morning and late afternoon sun but not overhead direct sun.  We haven’t found that Oakleafs tolerate hot sun well. Hydrangea paniculata and arborescens can tolerate more, but again, we prefer to give them a break from any intense sun.

2. We are firm believers in compost! Add a 2 inch top mulch in late winter and in the fall. Abundant compost has earthworms as well as humus and excellent nutrients. We avoid cow manure as it can be loaded with uncomposted clover seed which is a thug to contend with.

3. Water and water deeply.  We avoid mid-day watering as it can hurt the blooms.

4. Protect from winter winds. Plant in the correct location.

5. Plant in well-drained soil with a liberal addition of organic matter such as compost or Mushroom Compost.  We also like to incorporate polymers such as Soil Moist to help retain moisture. And mulch well with needles, soil conditioner or pine mulch.

6. Broadleaf trees like oaks, maples, beeches and hickories are fierce competitors for water and nutrients unless supplemental irrigation is provided.

7. Fertilize twice a year (early spring and half application in fall or HollyTone for blue hydrangeas and Plant Tone for pink).  Annabelles like fish emulsion every week as soon as they leaf out and until they bloom.

How do I dry mophead blooms (and Annabelles)?

It is all in the timing. Wait until blooms begin to feel “papery” or rustle when you touch them.  Cut early in the day and plunge stems in tepid water.  Strip all leaves.  Hold individual stems over a flame for 10 seconds then plunge the stem in ice water for 10 seconds.  String the stems together and hang upside down in a dark closet until dried, usually 2 weeks or less.

My climbing hydrangea isn't growing. What's wrong with it?

If it's only been in the ground for a year or two (or even three sometimes), probably nothing. Climbing hydrangeas are notorious for waiting a few years before growing vigorously. But when they get going, stand back...

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