Hydrangea care: from potted gift to garden shrub

Light

While it blooms indoors, give the plant bright light without hot sun on the leaves: in front of an east window, or right at a north one, which the Illinois Extension rates as medium light of about 150 foot-candles. A south window in full sun cooks the big, thin leaves. Outdoors the rule is clear and consistent across sources. Clemson asks for morning sun with afternoon shade and warns against hot, exposed sites, NC State says to protect it from afternoon sun, and Missouri Botanical Garden recommends part shade, adding that full sun is tolerated only in soil that stays consistently moist.

Shade has a limit, though. Clemson's pruning fact sheet notes that bigleaf hydrangeas need a minimum of 3 hours of morning sun to flower, and lists too much shade among the reasons a shrub stays green all summer.

Water

Hydrangea leaves are broad and soft, and Clemson notes that they lose moisture quickly. A gift plant usually arrives in a small pot crammed with roots, which dries out fast in a warm room. Check it often while it is in bloom and water whenever the surface feels dry, until water runs from the bottom. If the pot sits inside a foil sleeve, poke a hole or empty it after watering so the roots are never standing in water.

Once planted in the garden, Clemson advises watering deeply once a week, more often in dry weather, and up to twice weekly in sandy soil during hot summers. Consistent moisture is the goal: Clemson links it to preventing leaf scorch and flower loss. A 2- to 3-inch layer of mulch holds that moisture in; Missouri Botanical Garden suggests 3 inches of shredded bark, peat or compost year-round.

Midday wilting on a hot afternoon is common even in moist soil. If the leaves perk up by evening, the plant is fine; if they are still limp the next morning, it needs water now.

Soil and pH

Clemson describes hydrangeas as easy to grow in well-drained soil rich in organic matter, and NC State adds that the plant tolerates clay and sand and occasional wet soil. Soil chemistry also sets the flower color. Clemson explains that in acid soil, pH 5.0 to 5.5, aluminum is available and flowers turn blue, while at pH 6.0 and up they turn pink. Aluminum sulfate pushes toward blue and lime toward pink, and UF/IFAS warns the change may take two or three bloom cycles. Test your soil before adding either, as Clemson recommends.

Humidity

No source we used sets a humidity target for this shrub, and outdoors it grows in ordinary garden air. Indoors, the risk is the dry heat of a radiator or vent, which speeds water loss from those large leaves. Keep the pot away from heat sources and drafts while it blooms, and check the soil more often in a heated room.

Temperature

Hardiness is the real temperature question. Missouri Botanical Garden rates the species winter hardy to USDA Zone 6, with Zone 5 gardens needing a sheltered site and winter protection, and Clemson names winter injury as the most common reason hydrangeas fail to bloom. Flower buds are the weak point, since they sit on last year's stems. In a pot, the roots are more exposed than the canes: Clemson's cold damage fact sheet notes that unprotected roots in containers are especially vulnerable, with lethal root temperatures beginning at 28°F on some otherwise hardy species. If you overwinter it in a pot, mulch around it or move it to an unheated, sheltered spot.

Fertilizer

Clemson's schedule for bigleaf hydrangeas in the garden is a balanced fertilizer such as 10-10-10, applied in March, May and July at 2 cups per 100 square feet and watered in right away. A gift plant in bloom needs no feeding at all. More is not better: Clemson lists excess nitrogen among the reasons hydrangeas fail to bloom, so keep lawn fertilizer from washing into their root zone and skip feeding after midsummer.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

Moving a florist's hydrangea to the garden is the main transplanting job. Clemson recommends spring or fall planting, so a plant received in winter can wait indoors in a bright, cool spot until the ground is workable. Dig a hole two to three times as wide as the root ball but no deeper, backfill with the soil you removed, water deeply and mulch, following Clemson's planting steps. UF/IFAS warns against planting too deeply. Prune only right after flowering, never after August 1, or you remove next year's buds.

• Flowers have faded and the plant has outgrown its florist's pot
• Roots circle the pot and water runs straight through
• The pot wilts within a day of a thorough watering

Propagation

NC State lists layering and stem cuttings, and Clemson adds division. For layering, Clemson has you bend a flexible stem into a shallow trench, remove a 1-inch ring of bark from the buried section, and cover it with soil, leaving 6 to 12 inches of the tip exposed; it roots while still attached to the parent. Established clumps can be split with a shovel in early spring.

Methods: Layering, Stem cuttings, Division of established clumps · Best season: early spring for division; layering during the growing season.

Common problems

Failure to bloom is the classic complaint, and Clemson's list is short: winter injury first, then too much shade, poor soil fertility and excess nitrogen. Pruning after August 1 removes next year's flowers too. Leaf diseases come next; Clemson names Cercospora leaf spot, anthracnose and powdery mildew, and NC State adds bacterial wilt. UF/IFAS notes aphids and mites as occasional pests. Autumn leaf drop is normal for this deciduous shrub and not a sign of trouble.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the hydrangea toxic to cats and dogs?

The ASPCA lists hydrangea as toxic to cats, dogs and horses. Its entry carries the scientific name Hydrangea arborescens, a different species, but NC State gives the same class of toxin for Hydrangea macrophylla: hydracyanosides, which are cyanogenic glycosides. The ASPCA lists vomiting, depression and diarrhea as clinical signs and notes that cyanide intoxication is rare, usually producing more of a gastrointestinal disturbance. NC State rates severity for people as low, with nausea, stomach pain, vomiting and sweating after large quantities. If a pet eats leaves or flowers, call your veterinarian or the ASPCA Animal Poison Control Center.

Check any other plant against the ASPCA lists →