Nikko Blue Hydrangea

Hydrangea macrophylla 'Nikko Blue'

Nikko Blue is a bigleaf hydrangea with big, round clusters of flowers in late spring and summer. They're blue in acidic soil and pink in alkaline soil. It wants morning sun, afternoon shade, and steady moisture. All parts are mildly poisonous.

A close-up of a Nikko Blue hydrangea flower head packed with sky-blue four-petaled florets. — Flowers are blue when the soil is acidic.Photo: Iryna Buchnieva, Wikimedia Commons, public domain (CC0)

At a Glance

Plant type	Deciduous flowering shrub
Family	Hydrangea family (Hydrangeaceae)
Other names	Bigleaf hydrangea, mophead hydrangea, French hydrangea
Native range	The species is native to Japan, China, Korea, and Southeast Asia.
Mature height	About 4 feet. The species grows 3 to 6 feet.
Mature spread	About 4 feet
Flowers	Large, rounded mophead clusters in late spring and summer. Blue in acidic soil, pink in alkaline soil. Flowers mostly on the previous year's growth, and reportedly some on new growth.
Toxicity	The bark, leaves, and flowers contain cyanogenic glycosides. Eating large amounts can cause nausea, stomach pain, vomiting, and sweating in people. Toxic to dogs, cats, and horses, mainly causing vomiting, depression, and diarrhea. Severity is rated low.

Growing Conditions

USDA hardiness zones	6 to 11
Sun	Part shade. Morning sun with afternoon shade is ideal. Avoid hot, exposed sites.
Soil	Moist, well-drained soil rich in organic matter. Tolerates clay and sandy soil.
Soil pH	5.0 to 5.5 for blue flowers. 6.0 or higher turns them pink.
Water	Medium to high. Water deeply about once a week, more often in dry weather.
Tolerates	Clay, some salt
Does poorly with	Afternoon sun and heat, winter damage to flower buds, deer

Will It Grow Here?

Yes, anywhere in our area. Nikko Blue Hydrangea is hardy in zones 6 to 11, which covers every zone in our area (6b through 8a).

Zones in Southwest Missouri, Northwest Arkansas, Northeast Oklahoma, and Southeast Kansas
Zone	Grows here?	Towns in this zone
6b (our farm)	Yes	Lebanon, MO; Bolivar, MO; Iola, KS; Garnett, KS
7a	Yes	Springfield, MO; Joplin, MO; Fayetteville, AR; Bentonville, AR
7b	Yes	Harrison, AR; Tulsa, OK; Broken Arrow, OK; Tahlequah, OK
8a	Yes	Van Buren, AR; Alma, AR

Not sure which zone you're in? Look up your ZIP code on the USDA Plant Hardiness Zone Map (opens in a new tab).

Official 2023 USDA Plant Hardiness Zone Maps. Tap a map to open it full size.

Maps: USDA Agricultural Research Service, with mapping by the PRISM Climate Group, Oregon State University.

Plant Patent

We found no plant patent for 'Nikko Blue'. It's an older, widely grown variety. Check the plant tag before propagating.

About the Nikko Blue Hydrangea

Nikko Blue is one of the most common blue mophead hydrangeas. Bigleaf hydrangeas come from eastern Asia. Their flower color depends on the soil: blue in acidic soil and pink in alkaline soil.

Like other bigleaf hydrangeas, it forms most of its flowers on the previous year’s growth. Nikko Blue is reported to also flower some on new growth, which makes it more useful in colder areas.

Choosing a Spot

Morning sun, afternoon shade. Avoid hot, exposed spots. Too much shade cuts down on flowers.
Rich, moist, well-drained soil.
Test the soil. The pH decides the flower color: 5.0 to 5.5 for blue, 6.0 or higher for pink.
Deer. Deer eat hydrangeas.

Planting

Dig wide, not deep. Make the hole at least 1 1/2 to 2 times as wide as the root ball and only as deep. In poorly drained or compacted soil, make it 3 to 4 times as wide and not quite as deep.
Set the top of the root ball even with the surrounding soil or slightly above. Planting even 3 inches too deep lets water collect around the roots.
Slice circling roots. If roots circle the outside of the root ball, make three or four cuts an inch or two deep from top to bottom.
Backfill with the soil you dug out. Amendments usually aren’t needed.
Skip fertilizer at planting, and water right away.

Watering

New plants establish fastest with light, frequent watering. In summer a new shrub may need water several times a week. Overwatering kills as easily as drought, so feel the soil before you water. Once established, water deeply about once a week, and more often in dry weather. Drip irrigation is recommended.

Mulch and Fertilizer

Keep a 2 to 3 inch layer of mulch to hold moisture and keep the roots cool.

Too much nitrogen means fewer flowers. One extension guide suggests a balanced 10-10-10 fertilizer at about 2 cups per 100 square feet in March, May, and July, watered in right away.

Changing the color: For blue flowers, apply sulfur or aluminum sulfate when new growth appears in April. For pink flowers, apply lime. Test the soil first and retest every 2 to 3 years so you don’t overcorrect.

Pruning

Prune right after it flowers, and don’t prune after August 1. Later pruning can remove next year’s flower buds.

Common Problems

No flowers: Winter injury to the buds is the most common cause. Too much shade, poor soil fertility, and too much nitrogen also cut down on blooms.
Leaf diseases: Cercospora leaf spot, anthracnose, and powdery mildew. Rake up fallen leaves and water early in the morning or with drip irrigation.
Bacterial wilt can also occur.
Insects: Aphids, hydrangea leaftiers, and rose chafers.
Deer: Deer browse it.

Availability

Currently out of stock until Spring 2027.

Our nursery stock changes through the season. Contact us to check what we have on hand, current sizes, and pricing.

Sources

Growing information on this page was checked against these public references:

Disclaimer: The information on this page is based on publicly available knowledge and research. Individual results may vary.

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