Merritt’s Supreme Hydrangea (Hydrangea macrophylla ‘Merritt’s Supreme’) is a popular deciduous shrub known for its robust growth and impressive, rounded “mophead” blooms. These flowers display a range of vibrant colors from deep pink to rich purple-blue, adding visual appeal to gardens. Understanding its specific care requirements helps gardeners maximize its stunning floral display and ensure continued health.
Basic Care Essentials
Merritt’s Supreme Hydrangea thrives in specific light conditions for vigorous growth and abundant flowering. It performs best in partial shade, receiving indirect sunlight for much of the day. While it can tolerate full sun in cooler climates or morning hours, intense afternoon sun can scorch leaves and diminish flowers. Positioning the plant where it receives morning sun and afternoon shade generally provides optimal light for its health and blooming potential.
Consistent moisture is important for Merritt’s Supreme Hydrangea. The soil should remain consistently moist but never waterlogged to prevent root rot. During dry spells or high heat, regular watering is needed, sometimes twice a week. Mulching around the base helps retain soil moisture, reducing watering frequency.
This hydrangea prefers rich, well-drained soil that is high in organic matter. While it tolerates various soil compositions, including clay, loam, and sand, good drainage is necessary to prevent water accumulation around the roots. Amending heavy soils with coarse sand or organic material can improve drainage and aeration, fostering a healthier root environment. Soil pH is also important for overall plant health.
Merritt’s Supreme Hydrangea is hardy in USDA zones 6 to 9. It withstands cold temperatures down to -10°C (14°F) and heat up to 38°C (100°F). In warmer climates, adequate watering and partial shading help manage heat stress.
Planting and Fertilization
Selecting an appropriate planting location is important for the long-term success of Merritt’s Supreme Hydrangea. Choose a site that provides partial shade, especially protection from intense afternoon sun. When planting, dig a hole that is twice the diameter of the root ball and ensure the top of the root ball sits slightly above ground level to promote proper drainage. Loosening the soil around the root ball before planting encourages the roots to spread into the surrounding soil.
Merritt’s Supreme Hydrangea benefits from regular fertilization. Apply a balanced, slow-release granular fertilizer, such as a 10-10-10 formula, in early spring as new growth emerges. An additional application in mid-summer can also be beneficial. Broadcast fertilizer evenly around the plant’s base, avoiding direct contact with stems, and water thoroughly afterward.
Pruning for Optimal Growth and Blooms
Pruning Merritt’s Supreme Hydrangea, a mophead variety that blooms on old wood, is best done immediately after flowering, typically in late summer. This timing allows the plant to form new buds for the following year’s blooms. Deadheading spent flowers can also encourage new blooms.
Pruning aims to shape the plant, remove dead, weak, or diseased branches, and encourage vigorous growth. Cut flowering stems back to a pair of healthy buds, and remove weak shoots from the crown or lower stems. For older, overgrown plants, selectively remove one or two of the largest, oldest stems at the base to stimulate new growth.
Managing Bloom Color
The bloom color of Merritt’s Supreme Hydrangea, a Hydrangea macrophylla cultivar, is influenced by soil pH and aluminum availability. In acidic soils with sufficient aluminum, flowers are blue or purple-blue. In alkaline soils, blooms are pink or rosy-pink. Gardeners can manipulate flower color through soil amendments.
To achieve blue flowers, add aluminum sulfate to the soil. For pink blooms, incorporate lime to raise the soil pH. Apply these amendments well in advance of the blooming season, ideally in late fall or early spring, allowing soil chemistry to adjust. Test soil pH before applying amendments to determine the appropriate amount.
Common Problems and Solutions
Merritt’s Supreme Hydrangea generally exhibits good resistance to pests and diseases. Common pests include aphids and spider mites, which feed on plant sap, causing distorted leaves. If infestations occur, spray affected areas with insecticidal soap or neem oil, or remove infested plant parts.
Fungal diseases like powdery mildew and leaf spot can affect hydrangeas. Powdery mildew appears as a white coating on leaves, often due to high humidity and poor air circulation. Leaf spot diseases manifest as dark spots; minimizing leaf wetness helps prevent spread. Improving air circulation and promptly removing diseased leaves also manages these conditions. Troubleshooting wilting or yellowing leaves involves checking moisture levels and drainage, as both overwatering and underwatering cause stress.
Winter Care
Preparing Merritt’s Supreme Hydrangea for colder months protects its flower buds and ensures a vibrant bloom display the following spring. In colder parts of its hardiness range (USDA zones 6 and 7), providing additional winter protection is beneficial.
Apply a thick layer of organic mulch, such as shredded bark, peat, or compost, around the plant’s base to insulate roots from freezing temperatures. This layer should be 1 to 3 inches thick, spread around the plant but not touching stems. In exposed locations or areas prone to harsh winter winds and extreme cold snaps, covering the plant with burlap or a protective structure helps safeguard dormant flower buds.