Few shrubs say "Southern garden" like a big blue mophead hydrangea in full bloom beside a porch. Hydrangeas are generous plants: they flower for weeks, they make superb cut flowers, and their dried heads carry right on into fall decorating. They are also one of the plants people most often get wrong — usually by pruning at the wrong time or planting them where the afternoon sun is too harsh.
This guide covers hydrangea care for warm, humid climates: choosing the right type, siting and planting, watering, pruning and changing flower color.
Know which hydrangea you have
Almost every hydrangea question — especially "why didn't it bloom?" — depends on the type. The five most common in Southern gardens are:
- Bigleaf hydrangea (*Hydrangea macrophylla*). The classic mophead (round, pom-pom flowers) and lacecap (flat clusters). Flower color can be blue, pink or purple depending on soil. Blooms on old wood (last year's stems); reblooming varieties also bloom on new wood.
- Oakleaf hydrangea (*Hydrangea quercifolia*). Native to the Southeast, with oak-shaped leaves, cone-shaped white flowers and outstanding fall color. Blooms on old wood. More sun- and drought-tolerant than bigleaf.
- Smooth hydrangea (*Hydrangea arborescens*). Also native; includes the popular 'Annabelle', with large white globes. Blooms on new wood.
- Panicle hydrangea (*Hydrangea paniculata*). Cone-shaped white flowers that often age to pink. The most sun-tolerant type. Blooms on new wood.
- Mountain hydrangea (*Hydrangea serrata*). Similar to bigleaf but smaller and often hardier. Blooms on old wood.
If you are not sure what you have, look at the leaves and flower shape, or take a cutting to a local nursery.
Where to plant
In the South, the rule of thumb for bigleaf, mountain and smooth hydrangeas is morning sun, afternoon shade. Hot afternoon sun scorches leaves and makes plants wilt daily. Oakleaf and panicle hydrangeas tolerate more sun, but they still appreciate some afternoon relief in the hottest regions.
Plant in rich, well-drained soil amended with compost. Hydrangeas like consistent moisture but will rot in soggy ground. Give them room to reach their mature size — many bigleaf types grow 4 to 6 feet wide.
The best time to plant in the South is fall, when the soil is still warm but air temperatures are cooler, giving roots time to establish before summer.
Watering through summer
Hydrangeas are thirsty. The name itself comes from Greek words for water and vessel.
- Water deeply about once or twice a week, aiming for roughly an inch of water per week from rain and irrigation combined. Water more often in extreme heat and in the first year after planting.
- Water at the base, early in the morning, to reduce leaf disease.
- Mulch with 2 to 3 inches of pine straw, shredded bark or leaf mold to keep roots cool and conserve moisture.
- Do not panic at midday wilting. Bigleaf hydrangeas often droop in afternoon heat and recover by evening. If they are still wilted the next morning, they need water.
Pruning: the most important rule
Prune according to how your hydrangea blooms.
Old-wood bloomers: bigleaf, oakleaf, mountain
These set next year's flower buds in late summer and fall. Prune right after flowering, and no later than midsummer. Pruning in fall, winter or early spring cuts off next year's flowers — the most common reason hydrangeas fail to bloom. For these types, pruning is often unnecessary beyond removing dead stems and spent blooms.
New-wood bloomers: smooth and panicle
These form flowers on the current season's growth. Prune in late winter or early spring before new growth begins. You can cut smooth hydrangeas back hard; panicle hydrangeas can be shaped and thinned.
Reblooming bigleaf types
Varieties sold as reblooming or "remontant" bloom on both old and new wood. Light pruning after the first flush of flowers is safe.
Changing flower color
Only bigleaf and mountain hydrangeas with pink or blue flowers change color. White hydrangeas stay white.
Color depends on whether the plant can take up aluminum from the soil, which in turn depends on soil pH:
- Blue flowers: acidic soil, roughly pH 5.0 to 5.5, with aluminum available. To encourage blue, apply garden sulfur or aluminum sulfate according to the label.
- Pink flowers: neutral to alkaline soil, roughly pH 6.0 and above, where aluminum is less available. To encourage pink, add garden lime.
- Purple or mixed: somewhere in between.
Test your soil before adjusting, change pH gradually, and expect results to take a season or more. Plants growing near concrete foundations or sidewalks often turn pink because lime leaches from the concrete. Clemson Cooperative Extension's Home & Garden Information Center has detailed fact sheets on hydrangeas and soil testing for Southern gardeners.
Feeding
Hydrangeas do not need much fertilizer. A light application of a balanced, slow-release fertilizer in spring is usually enough. Too much nitrogen produces lush leaves and fewer flowers.
Common problems
- No flowers: usually pruning at the wrong time, late spring frost damaging buds, or too much shade.
- Brown, crispy leaf edges: heat stress or underwatering.
- Leaf spots: fungal leaf spot is common in humid weather. Water at the base, remove fallen leaves and improve air circulation.
- Yellow leaves with green veins: often a nutrient uptake problem related to soil pH.
Cutting and drying
For fresh arrangements, cut stems in the cool of the morning and plunge them into water immediately. To dry, wait until late summer when blooms feel slightly papery, cut them, remove the leaves and stand them in a vase with a couple of inches of water; let the water evaporate. Dried hydrangeas are a lovely, long-lasting element in fall porch decor.
If you love fragrant shrubs as much as showy ones, plant a gardenia nearby — our gardenia care guide covers their similar love of acidic soil and afternoon shade.
Frequently asked questions
Can hydrangeas grow in full sun in the South?
Panicle and oakleaf hydrangeas can handle more sun, especially with regular watering. Bigleaf hydrangeas usually struggle in full afternoon sun.
Should I deadhead hydrangeas?
You can remove spent blooms for tidiness. On old-wood types, cut just below the flower head and above the first set of healthy leaves, and do it by midsummer.
When is the best time to transplant a hydrangea?
In fall or late winter, when the plant is dormant or nearly so, and water well afterward.
Photo credits: Hydrangea macrophylla - Hortensia hydrangea by Raul654, CC BY-SA 3.0, via Wikimedia Commons; Hydrangea macrophylla 'Early Blue' 2017-10-15 01 by Agnieszka Kwiecien, Nova, CC BY-SA 4.0, via Wikimedia Commons.
