Plant Care Basics

How to Grow and Care for Big Leaf Hydrangea

Discover practical advice for growing healthy big leaf hydrangeas. Learn key techniques for proper care to ensure reliable, showy blooms season after season.

The big leaf hydrangea (Hydrangea macrophylla) is a popular garden staple, known for its large flower heads that bloom throughout the summer. These shrubs produce either large, globe-like mophead blooms or the more delicate, flattened lacecap flowers. With varieties offering colors from blue and pink to white, this plant has an appeal that suits many garden designs.

Planting and Ideal Location

Proper placement is the first step toward a thriving big leaf hydrangea. These plants flourish with morning sun and shade during the hot afternoon. This exposure provides enough light for robust blooming while protecting the large leaves from scorching. In cooler northern climates, they can tolerate more direct sun, but in warmer southern zones, afternoon shade is a requirement.

Big leaf hydrangeas perform best in rich, well-draining soil that remains consistently moist. Heavy clay soils can be improved by incorporating organic matter like compost, which helps with drainage and moisture retention. When planting, dig a hole two to three times wider than the nursery pot but just as deep. The top of the root ball should be level with or slightly above the surrounding soil surface.

After placing the plant in the hole, backfill the space halfway with soil and water it thoroughly to settle the plant. Finish filling the hole and add a 2- to 3-inch layer of organic mulch, such as shredded bark or pine straw. This layer helps conserve soil moisture, keeps the roots cool, and suppresses weeds.

Routine Care and Maintenance

Consistent moisture is key to the health of big leaf hydrangeas, whose large leaves lose a significant amount of water. The soil should be kept evenly moist, which may require watering one to three times per week during hot and dry periods. A deep watering that ensures moisture reaches the entire root system is more effective than frequent, light sprinklings. During the first few years after planting, regular watering is important as the plant establishes itself.

To support vigorous growth and abundant flowering, these shrubs benefit from fertilization during the growing season. A general-purpose, balanced fertilizer like a 10-10-10 formulation can be applied in the spring. For reblooming varieties, monthly applications from early spring until late July can encourage the development of new wood that will produce later-season flowers.

Big leaf hydrangeas are hardy in USDA zones 6 through 9. In colder regions, they may require winter protection. After the first hard frost, applying a thick layer of mulch around the base of the plant can insulate the roots. Covering the plant with a sheet or burlap when a late spring frost is predicted can protect new growth and flower buds.

Pruning Big Leaf Hydrangeas

Understanding how and when to prune is specific for big leaf hydrangeas because most varieties bloom on “old wood,” which are the stems that grew during the previous year. Pruning at the wrong time is a common reason for a lack of flowers. The most significant mistake is cutting the plant back in the fall, winter, or early spring, as this removes the dormant flower buds.

The best time to prune is in the late summer, immediately after the plant has finished its main flowering cycle. This timing allows the hydrangea to recover and produce the stems that will carry next year’s blooms before it enters dormancy. Pruning should be selective, and you can remove the spent flower heads to tidy the plant’s appearance.

You can also cut out any dead, damaged, or weak stems at their base to improve air circulation. Avoid cutting back healthy, established stems, even if the shrub seems large. If size control is necessary, selectively remove one or two of the oldest, thickest canes down to the ground to encourage new growth from the base without sacrificing an entire season of blooms.

Managing Flower Color

One of the most unique traits of Hydrangea macrophylla is the ability of most non-white varieties to change their flower color based on soil chemistry. The color is determined by the soil pH and the availability of aluminum ions in the soil. Gardeners can manage these factors to influence whether their hydrangeas produce blue or pink blooms.

To encourage blue flowers, the soil must be acidic, with a pH between 5.2 and 5.5, and contain aluminum. You can increase acidity by applying a soil acidifier or aluminum sulfate, found at garden centers. Following the product’s instructions, broadcast it over the root zone and water it in, a process that may need to be repeated to maintain the low pH.

Conversely, to achieve pink or red flowers, the soil needs to be alkaline, with a pH of 6.0 or higher. In alkaline conditions, the plant is unable to absorb aluminum from the soil, which prevents the blue pigment from developing. To raise the soil’s pH, you can amend it with garden lime. The amount needed will depend on the starting pH of your soil and may require periodic applications.

Common Issues and Solutions

A frequent concern for gardeners is a big leaf hydrangea that fails to bloom. The most common cause is improper pruning, specifically cutting back the stems in the fall or spring, which removes the flower buds formed on old wood. Cold damage from a late spring frost can also kill the vulnerable buds, and insufficient sunlight can lead to poor flowering.

Pests are not a major problem for these hydrangeas, but aphids can sometimes appear on new growth. They can be managed by spraying them off with a strong jet of water or by using insecticidal soap if the infestation is heavy. Diseases like powdery mildew and leaf spot can also occur, particularly in humid conditions with poor air circulation.

To prevent fungal diseases, ensure the plant has good air movement and water the soil directly rather than wetting the foliage. If disease does appear, removing the affected leaves can help slow its spread. A healthy, well-watered, and properly sited plant is more resistant to both pests and diseases.

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