blue hydrangea blossoms

Bigleaf hydrangea (H. macrophylla)

Updated: October 19, 2021

Key points

  • Hydrangeas (Hydrangea spp.) are popular flowering shrubs in Maryland gardens that are easily recognizable by their big blue, pink or white flower heads.
  • The ‘showy’ part of many hydrangea blooms have sterile flower parts that do not provide the pollen necessary to support pollinators. The fertile flower parts are much smaller, less showy, and do support pollinators.
  • Pruning at the wrong time of year for the variety of hydrangea is the most likely reason that hydrangeas fail to bloom. Follow the hydrangea pruning web page information. 

Growing hydrangeas in Maryland

  • There are many varieties of hydrangea that grow and thrive in Maryland, each comes with a different set of growing requirements. Don’t assume that their requirements are interchangeable.
  • Smooth hydrangea (Hydrangea arborescens) and Oakleaf hydrangea (Hydrangea quercifolia) are native species. 
  • Plant labels may say hydrangeas can take full sun. But planted in full sun, they will require more water and the bloom period may be reduced. Sunburn on the foliage and blooms is also possible since several species are adapted to woodland habitats".
  • Most plant problems can be avoided by providing plants with what they need to thrive, not just survive.

 Smooth hydrangea (Hydrangea arborescens)

  • Native to the eastern United States, including Maryland. 
  • Prefers moist, rich soils in partial sun or shade.
  • Flowers appear in June and are typically white, though some pink cultivars have recently been introduced. Many flowers are green when they begin to open. A second flush may appear in August or September.
  • Blooms on the current season’s growth (new wood)
  • Visiting insects (faunal associations) | Illinois Wildflower Association 

Oakleaf hydrangea (Hydrangea quercifolia)

  • Large white blooms late June - July on the previous season’s wood (termed “old wood”). The blooms of some cultivars age to pink.
  • Prefers partial shade in moist soil.
  • Prune immediately after flowering, if needed.
  • Renewal prune old or weak stems, to keep growth under control and rejuvenate the shrub.
  • This species tends to reliably display showy fall foliage colors like plum-red, burgundy, scarlet, and orange, unlike many other hydrangeas.
  • Native to the Southeastern US, though not into Maryland.

Bigleaf hydrangea (Hydrangea macrophylla)

  • Bloom time is from mid-June into August. The flower color palette of this group is the most diverse of all the hydrangeas, from white to various shades of pink, rosy near-red, purple, and true blue.
  • Blooms appear from buds from the previous season’s growth (old wood). 
  • Deer browse plus extremely cold low temperatures, periods of drought, late frosts, or other weather extremes can result in the death of overwintering flower buds. For cultivars that cannot rebloom, this prevents flowering the following summer.
  • Soil acidity (pH) affects the flower color of most cultivars except those with white flowers. Acidic (low pH of 5.0 - 5.5) soils will produce blue flowers. Use sulfur or iron sulfate to lower the soil Ph instead of aluminum sulfate (AS). Too much (AS) can damage or burn roots causing plant damage. 
  • Slightly acidic or alkaline soils (pH of 6.0 - 6.5) will produce flowers in the pink range. Purples or all three colors are possible in-between.
  • Prefers rich, well-drained soil in part sun to part shade.
  • Requires regular watering in dry weather. Mulching helps to maintain soil moisture, especially in full sun. This species may wilt when daytime temperatures are high, even if the soil is sufficiently moist, especially if the plant is in full sun. If plants recover at night and the soil isn’t dry, heat stress is the cause and supplemental watering is not needed.
  • Cultivars of bigleaf hydrangea are available that are more winter hardy, have longer blooming periods due to the ability to re-bloom, larger flowers, different shaped blooms, and other desirable characteristics. New cultivars are frequently introduced into the nursery trade every growing season.

Panicle hydrangea (Hydrangea paniculata)

  • Blooms on new wood starting in mid-July. Flowers are largely white, though some forms begin lime-green and others age to pink, though the richness of the pink color may depend on cooler temperatures.
  • Prune in winter or early spring.
  • Prefers rich, loamy, well-fertilized soil in full sun to partial shade.
  • Mulch around the base of the plant to help to maintain moisture.
  • H. paniculata 'Grandiflora' is an old cultivar that gives the group its other common name, PeeGee or P.G. hydrangea.

 

Problems and disorders of hydrangeas

Lack of Blooms

  • Pruning. Pruning at the wrong time of year is the #1 reason for no flowers on hydrangea. Some varieties of hydrangea bloom on the current season’s growth. Other varieties, like bigleaf hydrangea, bloom on the previous season's stems. Follow our Guide to Pruning Hydrangeas.

  • Over pruning. If your hydrangea died to the ground after a severely cold winter or if it was pruned too drastically, it may not bloom until the following year.

  • Over fertilization. Nitrogen, one of the 3 main components of fertilizers, promotes green leafy growth. Hydrangeas fertilized excessively with a high-nitrogen fertilizer can sometimes reduce flowering. If you fertilize, be sure it is balanced in N-P-K (nitrogen, phosphorus, potassium) or has a high phosphorus content. Bone meal provides a good source of phosphorus.

  • Deer. Hungry deer will eat tender new flower buds and foliage all year if not protected.

  • Late frosts. Late spring frosts can damage flower buds and leaves.

Undesired Flower Color

  • Have your soil tested to determine the pH of your soil.
  • Hydrangea macrophylla (big-leaf hydrangea) flowers can be pink or blue depending on the pH (acidity) of the soil. Blue flowers are produced when the pH of the soil is low or acidic making aluminum more readily available. When the pH is higher or more alkaline, aluminum is less available for the plants, and pink flowers result.
  • Avoid the use of aluminum sulfate unless trying to turn pink flowers to blue.

Scorched Leaves

Late spring frost often damages newly expanded hydrangea leaves. Leaves can appear burnt, black, or the margins (leaf edges) turn brown and crispy. Later in the season, leaves can be damaged, especially on hydrangeas planted in too much sun. Symptoms begin on the leaf margins. They will turn brown and dry.

frost damaged hydrangea leaves
Late frost damage on new leaves
Photo: Ask Extension

Wilting Leaves

Hydrangeas are one of the first plants to wilt during dry periods and if planted in full sun.

Hydrangea diseases

Bacterial leaf spot

bacterial leaf spot on hydrangea
Bacterial spot on oakleaf hydrangea.
Photo: Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org
  • Oakleaf hydrangeas (Hydrangea quercifolia) may develop reddish-brown or purple leaf spots – symptoms of bacterial leaf spot caused by Xanthomonas campestris in June. This disease commonly occurs during warm, wet weather in late spring and early summer.
  • While other hydrangea species, such as H. arborescens and H. macrophylla, are also susceptible, the disease seems to be most severe on oakleaf hydrangeas.
  • Symptoms are usually first observed on lower leaves, and the pathogen moves upward in the plant canopy through splashing water from rain or overhead irrigation. In the landscape, removing lower leaves as soon as leaf spots are first observed can help slow down the spread of disease.
  • Overhead irrigation of hydrangeas should be avoided or timed to keep leaf wetness periods to a minimum. In nurseries, increased plant spacing can help increase air circulation, since keeping foliage as dry as possible reduces the spread of the disease.

Fungal leaf spot

  • Fungal leaf spot is caused by Cercospora hydrangea, it disfigures the leaves when it develops in late summer and fall causing tan to gray lesions with dark purple halos.
  • It is more common in newly purchased plants that were grown in crowded conditions or on plants in poor health. While unsightly, the damage is not fatal and rarely warrants treatment.

Hydrangea pests

Cottony camellia scale

white sacs created by cottony camellia scale on a leaf
Cottony camellia scale
Photo: Brian Kunkel, University of Delaware, Bugwood.org

Cottony camellia scale is a sucking insect that feeds on the undersides of leaves. The feeding activity produces honeydew that grows sooty mold on the top side of the leaves.

Additional resource

Ohio State University Extension | Selecting Hydrangeas for the Home Landscape