Repotting guide

When & how to repot Bigleaf Hydrangea 'Nikko Blue' (Hydrangea macrophylla 'Nikko Blue')

Also called Nikko Blue Mophead.

More about bigleaf hydrangea 'nikko blue'

About Bigleaf Hydrangea 'Nikko Blue'

Hydrangea macrophylla 'Nikko Blue' · also called Nikko Blue Mophead · flowering

'Nikko Blue' is a classic mophead bigleaf hydrangea with large rounded flower heads that turn vivid blue in acidic soil or pink in alkaline soil. A vigorous deciduous shrub blooming in summer on old wood, it needs moist, rich soil and shelter, and rewards correct pruning with its signature voluptuous blue domes.

Mature size: 1.2-1.8 m tall and 1.2-1.8 m wide.

Watch for — Frost-killed buds: Late frosts kill the exposed old-wood buds, giving a flowerless year; plant in a sheltered spot and leave old growth on over winter for protection.

How to tell bigleaf hydrangea 'nikko blue' needs repotting

Repotting on a calendar is less reliable than reading the plant. For bigleaf hydrangea 'nikko blue', watch for these signs:

Roots spiralling thickly out of the drainage holes or pushing the whole plant up out of the pot.
The pot is so packed that water runs straight through in seconds and barely wets the soil.
It has split a plastic pot, or the rootball is a solid mass with almost no soil left when you slide it out.
Growth and (for bigleaf hydrangea 'nikko blue') flowering have clearly stalled despite good light and feeding — but remember this plant likes being snug, so a little crowding alone is not a reason to repot.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot bigleaf hydrangea 'nikko blue'

Only every 2–4 years, when genuinely crowded. Bigleaf Hydrangea 'Nikko Blue' is one of the plants that genuinely prefers a snug pot — it grows and flowers better with its roots a little restricted, so resist the urge to repot it on schedule. Rounded, multi-stemmed deciduous shrub with large coarse leaves; blooms on old wood (last year's stems), so flower buds form in late summer for the following year..

What size pot to step bigleaf hydrangea 'nikko blue' up to

Go up only one pot size — roughly 2–3 cm (about an inch) wider in diameter, no more. Bigleaf Hydrangea 'Nikko Blue' positively prefers a snug pot: it flowers and grows better when the roots are a little restricted. The single biggest repotting mistake here is over-potting — dropping bigleaf hydrangea 'nikko blue' into a pot two or three sizes up. All that surplus soil holds water the small root system cannot use, stays cold and wet, and rots the roots within weeks. When in doubt, choose the smaller pot.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot bigleaf hydrangea 'nikko blue'

Early spring, just as new growth restarts, is the ideal window for bigleaf hydrangea 'nikko blue'. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting bigleaf hydrangea 'nikko blue'

Confirm it actually needs it. Slide bigleaf hydrangea 'nikko blue' out and check the roots. Only continue if it is genuinely packed — this plant prefers a snug pot, so if there is still soil and room, put it straight back.
Pick a pot only one size up. Choose a pot just 2–3 cm wider with good drainage. Resist anything bigger; over-potting is the main killer here.
Ease it out gently. Water lightly the day before, then tip bigleaf hydrangea 'nikko blue' out, supporting the base. Tease the outer roots free only enough to stop them circling.
Repot at the same depth. Add a layer of fresh rich, moist, well-drained soil, set the plant so the soil line sits exactly where it did before, and backfill around the sides, firming lightly.
Settle it in. Water once to settle the soil, then let it sit. Hold off on more water until the top of the soil dries — fresh soil around a small root system stays wet for a while.

Aftercare

Because the new soil holds more water than the old crammed rootball did, ease right back on watering — let the top of the soil dry before you water bigleaf hydrangea 'nikko blue' again, or you will rot the roots in the very pot you just moved it to. Keep it out of harsh direct sun for a fortnight. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for bigleaf hydrangea 'nikko blue'

Bigleaf Hydrangea 'Nikko Blue' wants rich, moist, well-drained soil. Fertile, humus-rich, free-draining soil. Flower colour is pH-driven: acidic soil (pH below 5.5) with available aluminium gives blue, alkaline soil (above 6.5) gives pink. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting bigleaf hydrangea 'nikko blue' — frequently asked questions

How often should you repot bigleaf hydrangea 'nikko blue'?

Only every 2–4 years, when genuinely crowded for bigleaf hydrangea 'nikko blue'. Only repot bigleaf hydrangea 'nikko blue' every 2–4 years, and only when it is genuinely root-bound — it flowers and grows best slightly crowded. Step up just one pot size in spring using rich, moist, well-drained soil. The key mistake is over-potting: a too-big pot stays wet and rots the roots.

What size pot does bigleaf hydrangea 'nikko blue' need?

When is the best time of year to repot bigleaf hydrangea 'nikko blue'?

Does bigleaf hydrangea 'nikko blue' like to be root-bound?

Yes — bigleaf hydrangea 'nikko blue' genuinely flowers and grows best when slightly pot-bound, so do not rush to repot it. The mistake to avoid is over-potting into a much larger pot: the excess soil stays wet, the roots cannot use it, and the plant rots. Only repot every few years and only one snug size up.

Should you fertilise bigleaf hydrangea 'nikko blue' after repotting?

Not immediately. Wait about 4 weeks after repotting bigleaf hydrangea 'nikko blue'. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.