In a full-sun or partially shaded site and moist, well-drained soil, an oakleaf hydrangea (Hydrangea quercifolia) thrives with little care. This upright, deciduous shrub is a North American native plant that grows in the wild in stream banks, ravines, bluffs and moist woods. Hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9, oakleaf hydrangea grows 6 to 8 feet tall and wide. Pests and diseases rarely attack this shrub.
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Growing Oakleaf Hydrangea
Oakleaf hydrangea grows best in fertile, acidic soil, but tolerates a range of soil types. The shrub grows in sand, clay and loam soils, and tolerates slightly alkaline soil. Moist soil gives the best growth and flowering, though oakleaf hydrangea survives moderate drought. It doesn't tolerate salt exposure.
Grow an oakleaf hydrangea so that its central stem is 36 to 60 inches from other shrubs or trees. Over time, oakleaf hydrangea grows into a multi-stemmed shrub.
Watering and Fertilizing
Regular watering benefits an oakleaf hydrangea, but the shrub rarely needs fertilizer. Water oakleaf hydrangea while the shrub is in leaf, so that the soil surface stays moist to the touch, but don't apply so much water that the ground becomes soggy. When the shrub's leaves have fully expanded, spread a layer of garden compost, leaf mold, shredded bark or other organic mulch 2 to 3 inches thick. This helps retain moisture in the soil over summer. Don't allow the mulch to touch the shrub's stems.
Fertilizing oakleaf hydrangea encourages leafy growth but reduces flowering. Only apply fertilizer if the shrub shows signs of nutrient deficiency, such as slow, weak growth and small, pale leaves. Fertilize a nutrient-deficient oakleaf hydrangea with a granular, 12-4-8 fertilizer as soon as deficiency symptoms appear, and every three months while the shrub is in leaf. Sprinkle the granules at a rate of 4 tablespoons per 4 square feet on the soil surface over the shrub's root area, or apply the fertilizer according to the manufacturer's instructions.
Pruning the Shrub
An oakleaf hydrangea usually needs little pruning, but you can prune for shape and to remove dead or damaged wood. Wipe pruning shear and pruning saw blades with a cloth that was dipped in rubbing alcohol, before and after pruning the shrub. After flowering is over, prune stems that spoil the oakleaf hydrangea's shape where they join the rest of the shrub.
Harsh winters sometimes damage an oakleaf hydrangea. When new growth appears in spring, prune dead stems where they meet living wood, and prune damaged stems 2 to 3 inches into healthy wood, just above an outward-facing leaf bud.
Protecting From Frosts
In USDA zone 5, protecting oakleaf hydrangea from frosts can save its flower buds. Severely cold temperatures damage oakleaf hydrangea flower buds, which reduces or prevents flowering in the coming growing season.
To protect an oakleaf hydrangea from heavy frosts, surround the shrub with a cylinder of chicken wire in late fall when the branches are bare. Fill the chicken wire with dead leaves, straw or hay, and wrap burlap around the outside. Tie the burlap in place with twine. When new leaves appear in spring, remove the burlap, and one week later, remove the chicken wire and filling. If a late, hard frost is forecast in spring, cover the shrub in burlap overnight.