Do you know when to prune your hydrangeas? Knowing which species or cultivar you have will determine when you need to prune.
Bigleaf hydrangeas (Hydrangea macrophylla) flowers on old wood, which develop in late summer and fall. Pruning on these hydrangeas should be done immediately after flowering. Be careful to only remove one third of the total growth of the plant. The Endless Summer® cultivar series is an exception to this rule. The first flush of flowers of Endless Summer® usually bloom on old wood so any pruning should be done immediately after blooming. Flower buds will then form on new wood and the Endless Summer® hydrangeas will repeat bloom throughout the summer. The smooth hydrangeas (Hydrangea arborescens) and panicle hydrangeas (Hydrangea paniculate) develop flowers on new wood produced during the current growing season. Because they develop flowers on new growth, they can be pruned in late winter or early spring while the plants are dormant and before new growth begins.
Oakleaf hydrangeas (Hydrangea quercifloia) flowers develop on old wood from last year’s growth. Oakleaf hydrangeas bloom in June and should be pruned soon after flowering to maintain a desired size and shape. Pruning after they flower allows these beautiful native hydrangeas time to develop flower buds for next year.
Flower color on hydrangeas is determined by the soil pH, which affects the availability of aluminum in the soil. In acidic soils, the flowers will be blue. In alkaline soils, the flowers will be pink. Aluminum is available to the plant in acid soils. The color variation is due to the presence or absence of aluminum compounds in the flowers.
For blue flowers, maintain a soil pH between 5 and 5.5. Apply aluminum sulfate or sulfur to reduce the pH to this range when you see new growth emerging in April. For pink flowers, maintain a soil pH of 6 or higher by liming your soil.
Hydrangeas grow in well-drained soil. Hydrangeas, especially bigleaf, prefers morning sun and afternoon shade. Avoid planting in a hot, dry, exposed site. Many people purchase hydrangeas when they are blooming, but spring or fall is the best time to plant them.
Hydrangeas need ample moisture and afternoon shade to prevent wilting. Plan to water thoroughly once per week or more frequently.
Hydrangeas can be propagated by layering. Dig a trench near the plant and bend a section of limb down into the trench. Use a knife to remove a small ring of outer bark about an inch wide all the way around the limb. Cover the limb with soil leaving 6-12 inches of the top growth uncovered. Old established hydrangeas may also be divided in early spring by using a shovel to divide the clump.
For more information on hydrangeas, please visit the Home and Garden Information Center website at hgic.clemson.edu. Tune in on Tuesday nights to watch “Making it Grow” at 7pm on SCETV or mig.org. Email Outen at callenb@clemson.edu.
*Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs, sexual orientation, gender identity, marital or family status and is an equal opportunity employer.
