Repotting guide

When & how to repot Acer japonicum 'Aconitifolium' (Acer japonicum 'Aconitifolium')

Also called Fullmoon Maple, Fern-leaf Fullmoon Maple.

More about acer japonicum 'aconitifolium'

About Acer japonicum 'Aconitifolium'

Acer japonicum 'Aconitifolium' · also called Fullmoon Maple, Fern-leaf Fullmoon Maple · flowering

This fullmoon maple cultivar carries large, rounded leaves so deeply cut they resemble fern fronds, turning brilliant crimson, orange and gold in autumn. Small reddish flowers appear in spring. A choice slow-growing specimen with an elegant layered habit, it suits sheltered woodland-edge planting and large containers in cooler temperate gardens.

Mature size: 4-6 m tall and 3-5 m wide after many years; smaller and slower in containers.

Watch for — Leaf scorch: The deeply dissected leaves brown at the margins in sun, wind or dry soil; plant in dappled shade with shelter and keep the rootzone moist.

How to tell acer japonicum 'aconitifolium' needs repotting

Repotting on a calendar is less reliable than reading the plant. For acer japonicum 'aconitifolium', watch for these signs:

Thick roots out of the drainage holes, or circling the surface and lifting the plant.
The pot dries out unusually fast and acer japonicum 'aconitifolium' wilts between waterings it used to shrug off.
The plant is visibly top-heavy and tips over easily.
Stalled growth and small new leaves over a full season — though with a big specimen, top-dressing is often the better first response before a full 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 acer japonicum 'aconitifolium'

Every 2–3 years; top-dress in the in-between years. Acer japonicum 'Aconitifolium''s growth habit — slow-growing, rounded deciduous large shrub or small tree with a spreading, gently layered branch habit. — sets the pace. This fullmoon maple cultivar carries large, rounded leaves so deeply cut they resemble fern fronds, turning brilliant crimson, orange and gold in autumn. Small reddish flowers appear in spring. A choice slow-growing specimen with an elegant layered habit, it suits sheltered woodland-edge planting and large containers in cooler temperate gardens.

What size pot to step acer japonicum 'aconitifolium' up to

Move up exactly one pot size. A heavy acer japonicum 'aconitifolium' dropped into a vastly bigger pot sits in a reservoir of wet soil its roots cannot reach, which rots them and destabilises the plant. In the years between repots, lift off and replace the top 3–5 cm of soil (top-dressing) instead — it refreshes nutrients without the shock of a full repot.

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 acer japonicum 'aconitifolium'

Early spring, just as new growth restarts, is the ideal window for acer japonicum 'aconitifolium'. 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 acer japonicum 'aconitifolium'

Consider top-dressing first. If acer japonicum 'aconitifolium' is not badly root-bound, scrape off and replace the top 3–5 cm of soil instead — far less shock for a big plant that hates moving.
Get help and one size up. For a full repot, choose a pot just one size larger. A heavy plant needs two people and a stable, free-draining pot.
Ease it out on its side. Lay the plant down, slide the pot off, and gently loosen the outer roots. Do not bare-root a mature specimen.
Repot at the same depth. Add fresh humus-rich, moisture-retentive, well-drained acidic to neutral loam beneath and around the rootball, keeping the original soil line. Firm it so the trunk is stable and upright.
Water and leave it put. Water thoroughly, then leave acer japonicum 'aconitifolium' in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave acer japonicum 'aconitifolium' in exactly the same spot and light it was in before — moving and repotting at the same time is what makes a big specimen drop leaves. Water it in well, then let the top of the soil dry before watering again so the larger volume of fresh soil does not stay sodden. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for acer japonicum 'aconitifolium'

Acer japonicum 'Aconitifolium' wants humus-rich, moisture-retentive, well-drained acidic to neutral loam. Prefers slightly acidic, fertile soil high in organic matter. Dislikes thin chalk, drought and heavy waterlogging; in pots use a loam-based ericaceous-leaning mix with added grit. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting acer japonicum 'aconitifolium' — frequently asked questions

How often should you repot acer japonicum 'aconitifolium'?

Every 2–3 years; top-dress in the in-between years for acer japonicum 'aconitifolium'. Fully repot acer japonicum 'aconitifolium' only every 2–3 years; in the in-between years just top-dress the top 3–5 cm of soil. Step up one pot size in spring with humus-rich, moisture-retentive, well-drained acidic to neutral loam. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does acer japonicum 'aconitifolium' need?

When is the best time of year to repot acer japonicum 'aconitifolium'?

Should you top-dress or fully repot acer japonicum 'aconitifolium'?

For a big, heavy acer japonicum 'aconitifolium', top-dressing — replacing the top 3–5 cm of soil — is the gentler option most years, with a full repot only every 2–3 years. A mature specimen sulks and drops leaves when fully repotted, so do it as rarely as the roots allow.

Should you fertilise acer japonicum 'aconitifolium' after repotting?

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