Why are my hydrangeas not blooming?

They might have been pruned at the wrong time or suffered from late spring frost damage.

How do I make my flowers blue?

You need to increase soil acidity by adding aluminum sulfate or sulfur.

Plant guide

Hydrangea.

Hydrangea

Pronounced hy-DRAN-jee-uh mak-ro-FIL-uh

Also known as Hydrangea, Hydrangeas

mophead hydrangea — Photo by Claude Kolwelter (CC BY) via iNaturalist

Hydrangeas are beloved shrubs known for their massive, showy flower clusters. They thrive in spots with morning sun and afternoon shade. Depending on soil acidity, their blooms can shift between blue and pink.

At a glance

Care level: Moderate
Plant type: Deciduous shrub
Light: Partial shade
Indoor light: bright-indirect
Water: Every 2 to 4 days
Mature size: 1.5 to 2.5 meters
Growth rate: medium
Hardiness: USDA 5 to 9
Bloom time: Late spring to late summer

Care

Keep the soil consistently moist but never waterlogged to prevent root rot. Watch for wilting during hot afternoons, which is a sign the plant needs more shade or water. Prune only after flowering to avoid cutting off next year's buds.

Watering: Water deeply whenever the top inch of soil feels dry.
Feeding: Apply a balanced fertilizer in early spring and once more in mid summer.
Pruning: Prune immediately after the flowers fade to protect developing buds.
Repotting: Repot when the roots have filled the container or the plant stops growing.
Soil: Rich, well-draining, organic soil
Soil pH: Acidic to neutral
Temperature: -15 to 30°C
Humidity: 40 to 70%
Drought tolerance: low
Lifespan: Perennial, typically 10 to 20 years.
Fragrance: light
Deer and rabbits: low

Signs it needs repotting

Roots growing out of the drainage holes.
Water running straight through the pot without soaking in.
Stunted growth despite regular feeding.

Safety

People: All parts of the plant are considered toxic if ingested, potentially causing gastrointestinal distress.
Pets: Hydrangeas are toxic to cats and dogs if ingested, as they contain cyanogenic glycosides.
Children: Keep this plant away from small children as the leaves and flowers are toxic if chewed or swallowed.
Contact allergens: Handling the foliage may cause skin irritation or dermatitis in sensitive individuals.
Airborne allergens: The pollen is generally not considered a significant airborne allergen.
Edibility: Hydrangea leaves and buds contain cyanogenic glycosides and should never be consumed.

How to identify it

Large, serrated, ovate green leaves
Showy, rounded flower clusters
Woody, multi-stemmed shrub habit
Opposite leaf arrangement on stems

Height: 1 to 2.5m
Spread: 1 to 2.5m
Leaves: green, deciduous
Flowers: blue, pink, white, purple, 10 to 25cm

Common problems

Powdery mildew — A white fungal growth appears on leaves due to poor air circulation or high humidity.
Aphids — Small insects that cluster on new growth and suck plant sap.

Growing it

Propagation: cuttings, layering
When to plant: spring, autumn
Overwintering: Apply a layer of mulch around the base to protect roots from temperature swings. Avoid heavy pruning in autumn to protect potential flower buds.
In containers: They grow well in large pots, provided the container is at least 15 inches wide and has excellent drainage.

Softwood cuttings

Take a 6 inch cutting from a non flowering stem in early summer.
Remove the lower leaves and dip the end in rooting hormone.
Place in a moist potting mix and keep in bright, indirect light.

Group plants with similar water needs to ensure the hydrangea does not dry out.

Grows well with

Hostas — They share similar requirements for shade and moisture.
Ferns — Ferns provide a beautiful textural contrast in shade gardens.

Keep away from

Sunflowers — They compete for water and require vastly different light levels.

Similar species

Viburnum — They share similar shrubby habits and showy flower clusters.

Science

Family: Hydrangeaceae
Genus: Hydrangea
Order: Cornales
Class: Magnoliopsida
Native range: Primarily Eastern Asia and North America.
Conservation: Most common garden species are not of conservation concern, though some wild populations are protected.

Hydrangeas typically thrive in moist, shaded woodland environments where they can access consistent water.

Value to wildlife: nectar source, nesting habitat
Pollinators: bees, beetles
Uses: ornamental shrub, cut flowers, dried arrangements

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Light: 4/9
Salinity: 2/9
Soil reaction: 5/9
Temperature: 5/9
Moisture: 7/9
Nutrients: 6/9

Taxonomy resolved against GBIF.

Questions people ask

Why are my hydrangeas not blooming?: They might have been pruned at the wrong time or suffered from late spring frost damage.
How do I make my flowers blue?: You need to increase soil acidity by adding aluminum sulfate or sulfur.

Where the name comes from

The name Hydrangea is derived from the Greek words hydro, meaning water, and angos, meaning vessel, referring to the seed capsules. It was named by botanist Jan Frederik Gronovius.

Good to know

Hydrangeas have been cultivated for centuries in Japan.
The name comes from the Greek words for water and vessel.
Some species can produce both fertile and sterile flowers on the same bloom head.

Is your hydrangea looking unwell?

This page is a general guide. Pocket Botanist diagnoses problems from a photo of your actual plant, works out watering for your light and conditions, and reminds you when care is due.

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.