They look like snowballs out of a particularly pleasant dream, lacy globes as big as melons in soft shades of white, but also blues and pinks and lavenders. Snowball hydrangea (Hydrangea macrophylla), also called bigleaf or mop top, gives your garden a touch of fairy magic every spring; the dry bones of the shrubs fill with fresh green leaves, followed by the showy round blooms. When your bigleaf's health falters, the entire garden seems to wilt. Generally, reviving these hardy plants is a matter of establishing an appropriate irrigation schedule.
Increase irrigation or transplant the hydrangeas if you see leaves wilting after a hot day. Bigleaf hydrangeas need sun to bloom but prefer some shade on hot summer afternoons. Increase irrigation to compensate for the heat if you have plants that are in direct sun all day long. All hydrangeas require regular deep watering in summer, but those grown in hot sun need soil that is constantly moist. Apply 10 gallons of water every week per plant, irrigating slowly so that the water seeps down to the roots. Increase applications if wilting continues.
Provide more water if you notice distorted growth in new shoots, especially in hot, dry weather. Your hydrangea is likely infested by mites that attack water-stressed shrubs. Check for webbing between leaves to confirm the diagnosis. Avoid pesticides, which have little affect on the mite population; instead, irrigate appropriately to prevent and reduce a mite infection.
Inspect the hydrangea leaves. If they are covered with a pale powder, your plant has powdery mildew, which is the major disease problem in hydrangeas. The mildew is rarely deadly, so swift, decisive action is not required; first try changing cultural practices. Eliminate overhead watering in the afternoon as humid conditions allow spores to grow. Clip back neighboring vegetation to give the shrubs daily sun. Prune off infected leaves with garden clippers wiped with a rag soaked in denatured alcohol; dispose of the leaves. For extreme cases, spray both sides of the leaves with a mixture of 4 teaspoons of baking soda, 2 tablespoons of horticultural oil and 1 gallon of water. Apply every morning for a week.
Look for small yellow-green insects on the underside of young leaves or an army of ants swarming up the foliage. Aphids attack new growth, and the sticky honeydew they produce attracts ants. The problem diminishes as the leaves toughen. Wash the leaves with a high-powered hose spray to remove insects and then spray with a mixture of 2 ounces of dishwashing soap and 1 gallon of water. Treat again after 10 days.
Things You Will Need
- Garden clippers
- Clean rag
- Denatured alcohol
- Baking soda
- Horticultural oil
- Garden sprayer
- Dishwashing soap
- Even the most sensitive gardener is not likely to view a hydrangea with yellowing new leaves as dying, nor is it. The plant probably lacks iron. Add a chelated iron product to the soil around the plant's roots when you first notice the yellowing. Dissolve 2/3 ounce of a product containing 13.2 percent chelated iron into 10 gallons of water; pour over the root area of the shrub, avoiding moistening foliage.
- Improper or untimely pruning can reduce blossoms. Hydrangeas bloom on old wood. Prune immediately after the flowers fade.
- Fine Gardening: Hydrangea Macrophylla (Bigleaf Hydrangea)
- Missouri Botanical Garden: Hydrangea Macrophylla "Nikko Blue"
- The United States National Arboretum: Hydrangea Questions and Answers
- Huntree.com: Hydrangea Care
- Colorado State Extension: Powdery Mildews
- Good Earth Organic Rose Care: Mildew
- The Doggett Corporation: Ferro-Late xl Iron Chelate
- Creatas Images/Creatas/Getty Images