Bigleaf hydrangeas give gardeners a rare payoff: the soil itself decides the flower color. Very acidic soil yields blue blooms, less acidic soil produces purple or reddish flowers, and reblooming cultivars keep producing flower heads from early summer into fall. These compact shrubs reach about 3 to 4 feet tall and 4 to 5 feet wide, so the plant keeps a low profile beneath front windows and in mixed borders. They tolerate heat, resist powdery mildew, and grow quickly, which makes them a practical choice for both new and experienced gardeners.
This article covers where to plant reblooming hydrangeas, how to manage soil pH for the bloom color you want, how to prune and overwinter them, and how to protect them from pests and wildlife. All hydrangea parts are toxic to humans, cats, dogs, and horses, so site them where children and pets do not graze.
Why Reblooming Bigleaf Hydrangeas Stand Out
Most bigleaf hydrangeas bloom once per season on old wood, meaning the flower buds form the previous summer and wait out the winter on the stems. A hard freeze, a late frost, or an overzealous pruning cuts those buds off and the plant skips a year of flowers. Reblooming cultivars flower on old wood and new wood, so buds that form in spring on fresh growth open in the same season, and the shrubs keep setting buds for months. Breeders have kept raising the profile of these plants in northern gardens because the insurance of a second bloom cycle removes most of the risk.
Flower heads form the classic mophead shape, three to five inches across, made of many small florets. The stems carry a reddish-purple tint and the leaves are dark green with a slight gloss, which gives the shrub visual interest even between bloom cycles. Growth is fast, so a young plant fills a 4-foot-wide spot within two or three seasons.
Old Wood Versus New Wood Blooming
Understanding the two bloom cycles changes how you prune and how you react to weather. Old wood buds open in early summer; new wood buds open later and keep the show going. When a late frost kills the early buds, a reblooming shrub simply waits for the new flush instead of ending the season.
How a Late Frost Changes the Season
In zones 4 and 5, spring frosts arrive after the shrub has leafed out, and the first flower buds on old wood are the most exposed. With a reblooming type, the second flush from new wood still appears, so the garden keeps color even in a cold, uneven spring.
Heat and Disease Tolerance
Reblooming selections handle summer heat better than older bigleaf types, and breeders selected for powdery mildew resistance. That white coating on leaves, which ruins the look of many hydrangeas in humid summers, shows up far less on these cultivars, though no shrub is immune.
Planting Site, Soil, and pH
Site selection decides most of a hydrangea’s success. The shrubs want partial shade, with morning sun and afternoon shade in warm regions, and shelter from strong wind. Soil should stay moist but drain well, because standing water rots the roots while dry soil wilts the leaves by midday.
Light and Air Circulation
Too much shade produces thin growth and few flowers; too much afternoon sun bleaches the leaves and stresses the plant. A spot that gets four to six hours of morning light, with dappled shade by early afternoon, balances growth and bloom. Leave room between shrubs and walls so air moves through the canopy, which lowers disease pressure.
Soil pH and Flower Color
Bigleaf hydrangeas are unique because soil pH drives bloom color. Very acidic soil, below pH 5.5, makes aluminum available to the roots and the flowers open blue. Less acidic soil locks up the aluminum and the blooms come out purple or reddish. The table below shows the ranges most gardeners work with.
| Soil pH | Flower Color | Typical Adjustment |
|---|---|---|
| Below 5.5 | Blue | Add elemental sulfur or aluminum sulfate in spring |
| 5.5 to 6.5 | Purple or blue-purple | Test soil first, then adjust gradually |
| Above 6.5 | Pink or red | Add lime to raise pH over a season |
Step-by-Step Planting
Plant in spring after the last frost, or in fall at least six weeks before the ground freezes so roots establish before winter. Space plants 4 to 5 feet apart, since mature shrubs spread as wide as they are tall.
- Dig a hole twice as wide as the root ball and no deeper.
- Loosen the sides of the hole and mix compost into the backfill.
- Set the shrub so the crown sits level with the soil surface.
- Backfill, firm the soil, and water deeply.
- Add 2 to 3 inches of mulch, keeping it off the stems.
Watering and Mulch
New plantings need water once or twice a week through the first season. Established shrubs handle about 1 inch of water per week, applied at the base rather than over the leaves. Mulch holds soil moisture and keeps the roots cool, which bigleaf hydrangeas appreciate in summer.
Designing With Hydrangeas in the Landscape
Because reblooming hydrangeas stay compact, they work at the front of a border, along a foundation, or as a low hedge between the lawn and a patio. The shrubs read as soft mounds of dark green for most of the year, then carry color for months once the flowers open.
Foundation plantings deserve extra planning because roof eaves shed water unevenly and downspout splash keeps the soil wet against the wall. Before you plant beneath windows, inspect the frames overhead for rot and sealant gaps, since the PVC profile standards used in modern fenestration hold up better against repeated splash-back than older wood frames. A shrub that tops out near 4 feet also clears most window sills without blocking the view.
Foundation Plantings and Borders
Use a single cultivar in a row for a tidy hedge, or mix two or three hydrangeas with different bloom colors for a looser border. In narrow side yards, one shrub every 4 to 5 feet forms a soft screen without the maintenance of a clipped hedge.
Companion Plants for Shade and Moisture
Hostas and ferns share the hydrangea’s love of cool, moist soil and fill the space below the shrub’s canopy. Spring bulbs add early color before the hydrangea leafs out fully, and ornamental grasses provide contrast with upright texture.
Keeping Bloom Color Consistent
If you plant several hydrangeas in one bed, keep the soil conditions uniform so the flower color matches across the planting. A bed amended with the same compost and watered on the same schedule produces a more consistent show than plants scattered across different soil types.
Pests, Diseases, and Wildlife Protection
Powdery mildew resistance cuts the most common disease problem, but reblooming hydrangeas still face aphids, spider mites, and leaf spots in stressful seasons. Bud blight turns unopened buds brown, and root rot follows heavy, poorly drained soil. Good spacing, morning watering, and clean fall cleanup prevent most of these issues.
- Aphids cluster on new growth and buds; knock them off with a strong spray of water.
- Spider mites appear in hot, dry spells and leave stippled leaves; hose the undersides.
- Leaf spots show as brown or purple blotches; remove affected leaves and improve airflow.
- Bud blight blackens buds before they open; avoid overhead watering late in the day.
Deer and rabbits browse hydrangeas in winter and early spring, and rabbits chew the young stems at ground level. Fencing, netting, and a rotating repellent program give you access control over which animals reach the shrubs, the same principle site managers use to limit entry to fenced work areas. Protect young plants for the first two winters, when the damage does the most harm.
Signs of Stress to Watch
Wilting leaves at midday that recover by evening usually mean the soil is too dry. Yellowing leaves with green veins point to high pH locking up iron. Brown, crispy leaf edges often follow a long hot spell or salt buildup from heavy fertilizing.
Pruning, Overwintering, and Buying Plants
Reblooming hydrangeas need the least pruning of any hydrangea type. In early spring, remove dead stems and any growth damaged over winter, then thin a few of the oldest stems to open the center. Skip hard cutbacks, because the shrub needs its old wood for the first bloom flush.
A Simple Pruning Routine
Deadhead spent flower heads after they fade to tidy the plant, but leave the last ones of the season in place; they add winter interest and protect the buds below. Every three or four years, remove about a third of the oldest stems at the base to keep the shrub vigorous.
Winter Protection in Cold Zones
In zones 4 and 5, the stems and the buds on them need insulation. After the ground freezes, mound 6 to 8 inches of shredded leaves or bark over the crown, and wrap the stems in burlap where winter wind is harsh. Remove the mound gradually in spring once hard frosts end.
Buying Healthy Plants
Order shrubs from reputable nurseries and inspect them on arrival for wilting, discolored leaves, or pests in the soil. Gardeners who buy plants online can apply lessons from high-profile contractor arrests in construction: verify who you are dealing with, check reviews, and keep records of the transaction. A healthy, correctly named plant saves a season of frustration.
Getting the Bloom Color You Want
Bloom color is adjustable because it tracks soil chemistry. To shift blooms toward blue, lower the pH and make aluminum available; to shift toward pink, raise the pH. Changes take a season or two, so test the soil before you amend and adjust gradually.
- For blue flowers: add elemental sulfur or aluminum sulfate in spring, following package rates.
- For pink flowers: add lime in fall, then retest in spring.
- For purple: hold the pH near 6.0 and let the plant settle.
Retest the soil each spring, because rain and compost push pH back toward the starting point over time. For a full routine with rates and timing, see changing hydrangea color through soil pH adjustment and apply the steps to your own beds.
Testing and Adjusting Over Time
A soil test kit from a garden center or a county extension lab gives you a baseline. Adjust in small steps, retest in fall, and expect the deepest blues only where the soil stays acidic through the season. Container plants respond faster than in-ground plants because the root zone is smaller.