Hydrangea: Identify and Manage Problems

Bigleaf hydrangea (H. macrophylla)

Updated: February 6, 2024

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.

Tips for diagnosing plant problems

The majority of plant problems are not caused by a disease or an insect, especially if the plant has been in your landscape for less than two years. What causes trees and shrubs to die?

The presence of an insect or disease may not be the cause of the problem. Sometimes pests will take advantage of damaged or declining plants or the damage may have occurred way before you noticed it.

It is okay to tolerate some plant damage. For example, many fungal leaf spots cause cosmetic damage. Unsightly leaves can be simply pruned off the plant.

Poor growing conditions, incorrect care, weather extremes, and soggy soil are the major cause of plant decline.

Become familiar with normal plant characteristics throughout the year.

There are numerous parasitoids and predators that keep insect pests under control.

Use a pesticide only as a last resort and apply with care. First, identify the pest or disease and select low-toxicity products.

Problems and disorders of hydrangeas

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.

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.

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

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

Drought and excessive heat stress
Be sure to keep the root zone adequately moist. Watering guidelines for trees and shrubs

Hydrangea diseases

Bacterial leaf spot

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

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.

Related information

Pruning Hydrangeas

Pruning Shrubs and Hedges

Additional resources

Wild Hydrangea for the Mid-Atlantic Region | Research report from Mt. Cuba Center Trial Garden

Selecting Hydrangeas for the Home Landscape | Ohio State University Extension

Author: Ria Malloy, HGIC. 2021

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