Big Leaf Hydrangeas (Hydrangea macrophylla) are celebrated for their abundant, vibrant blooms. Their large, often globe-shaped or flat-topped flower clusters bring classic beauty to landscapes. Understanding their specific needs allows gardeners to cultivate healthy plants and impressive color displays. This guide provides information on planting and ongoing maintenance.
Planting Big Leaf Hydrangeas
Choosing the right location is the first step for thriving Big Leaf Hydrangeas. They prefer morning sun and afternoon shade, especially in warmer climates (USDA Zones 7+), where intense sun can scorch foliage. In cooler regions (USDA Zones 4-6), more direct sunlight is tolerated if soil is consistently moist and mulched.
Prepare the soil thoroughly. Big Leaf Hydrangeas thrive in moist, well-drained, organically rich soil. Amend existing soil with compost or other organic matter to improve drainage and fertility. Dig a planting hole two to three times wider than the root ball, but no deeper than its height.
Place the hydrangea in the hole, ensuring the top of the root ball is level with the soil surface. Backfill gently, firming soil around roots to remove air pockets. Water thoroughly after planting to settle the soil. Space multiple hydrangeas five feet apart for mature size and air circulation.
Essential Care for Thriving Blooms
Optimal light conditions are important for healthy growth and abundant flowering. Morning sunlight provides energy without intense midday heat. Afternoon shade protects large leaves from scorching, especially in warmer climates. Insufficient light reduces blooms, while too much direct sun causes leaf burn and wilting.
Consistent moisture is important for these water-loving plants. Their large leaves transpire significant water, requiring regular irrigation, especially during dry periods. Aim for one to two inches of water per week, delivered through deep waterings. Wilting can occur during extreme heat, but leaves recover as temperatures cool.
Maintaining healthy soil conditions contributes to plant vigor. Hydrangeas prefer consistently moist, well-drained soil to prevent root rot. Apply a two to three-inch layer of organic mulch (shredded bark, pine straw, compost) around the base to conserve moisture and keep the root zone cool. Mulching also enriches the soil as it breaks down.
Basic fertilization supports robust growth and prolific flowering. Apply a balanced slow-release fertilizer (e.g., 10-10-10 or 20-20-20) in early spring as new growth emerges. Reblooming varieties may benefit from an additional light feeding monthly until late July. Avoid fertilizing past mid-August, especially in colder climates, as late-season feeding promotes tender new growth vulnerable to winter damage.
Mastering Bloom Color
Big Leaf Hydrangea bloom color (pink, blue, or purple) is primarily influenced by soil pH. In acidic soil (pH 5.0-5.5), flowers are blue. In alkaline soil (pH 6.5+), blooms are pink. Purple or mixed shades appear in neutral to slightly acidic soils (pH 5.5-6.5). This variation occurs because soil pH affects aluminum availability, which the plant absorbs for blue pigmentation.
Test your soil’s pH before attempting color changes; knowing your baseline allows precise adjustments. White-flowered varieties always bloom white, regardless of soil pH. Some cultivars are less sensitive to pH changes and maintain their specific color more consistently.
To encourage blue blooms, lower soil pH to increase acidity and aluminum availability. Apply aluminum sulfate or wettable sulfur. A common method is dissolving one tablespoon of aluminum sulfate in one gallon of water and drenching the soil in early spring. Organic amendments like coffee grounds, pine needles, or oak leaves also contribute to soil acidity.
For pink flowers, raise soil pH to make it more alkaline, reducing aluminum uptake. Dolomitic lime is commonly used; apply one cup per ten square feet around the plant in fall or early spring. Avoid acidic fertilizers and mulches. Changing soil pH takes time, often requiring multiple applications over several months or a full year for a noticeable shift.
Pruning for Healthy Growth and Abundant Flowers
Understanding pruning needs is important for plant health and prolific blooms. Most traditional Big Leaf Hydrangeas bloom on “old wood,” forming buds on previous year’s growth. Incorrect pruning removes these buds, resulting in few or no flowers. Newer “reblooming” cultivars produce flowers on both old and new wood, making them more forgiving.
The optimal time to prune old wood blooming hydrangeas is immediately after flowering in late summer or early fall. This allows the plant time to develop new growth and set buds before winter. For reblooming varieties, light pruning can occur at various times, but avoid heavy pruning in late fall or winter.
Pruning should be minimal. Remove dead, diseased, or damaged branches at any time by cutting them back to healthy wood or the ground. For shaping or size reduction, remove up to one-third of the oldest or weakest stems each season at the base. Deadheading spent flowers improves appearance and may encourage reblooming varieties to produce additional flowers.
Winterizing Big Leaf Hydrangeas
Protecting Big Leaf Hydrangeas in winter (USDA Zones 4-5) is necessary for flower bud survival and abundant blooms. Traditional varieties form buds on old wood in late summer, making them susceptible to freezing temperatures and harsh winter winds. While the plant may survive cold, flower buds can be killed, leading to a lack of blooms.
Apply a thick layer of organic mulch around the plant’s base. After the ground freezes in late fall or early winter, spread six to eight inches of straw, marsh hay, fallen leaves, or pine bark over the root zone. This insulates the crown and roots from temperature fluctuations and prevents frost heaving.
For additional protection in severe winters, cover the plant. Construct a chicken wire cage and fill it loosely with insulating materials like straw or dry leaves. Alternatively, wrap the plant loosely with burlap to shield it from drying winds and direct cold. Ensure the plant is well-watered before the ground freezes, as hydrated tissues are more resilient. Remove coverings gradually in mid-spring once hard frosts pass.
Troubleshooting Common Problems
Big Leaf Hydrangeas can encounter issues affecting health and flowering. Lack of blooms often stems from winter injury to flower buds (late frosts, extreme cold) or incorrect pruning on old wood varieties. Insufficient light or too much nitrogen (promoting leafy growth over flowers) also contribute.
Yellowing leaves (chlorosis) indicate nutrient deficiencies or unsuitable soil pH. When pH is too high or low, the plant struggles to absorb essential nutrients. Apply a balanced fertilizer and ensure appropriate soil pH to resolve this. A soil test can pinpoint specific imbalances.
Wilting foliage signals overwatering or underwatering. Big Leaf Hydrangeas have large leaves that lose moisture quickly, requiring consistent hydration. If soil is dry, water the plant. Persistently wet or soggy soil leads to root rot, also causing wilting. Improve soil drainage and adjust watering frequency.
While robust, Big Leaf Hydrangeas can be susceptible to pests and diseases. Common fungal issues like powdery mildew, Cercospora leaf spot, and anthracnose manifest as spots or powdery coatings on leaves. To manage these, remove fallen leaves to reduce disease inoculum. Use drip irrigation or soaker hoses to water at the base, keeping foliage dry and minimizing fungal development. If using sprinklers, water early morning to allow leaves to dry quickly.