Repotting guide

When & how to repot Bigleaf Magnolia (Magnolia macrophylla)

Also called Bigleaf Magnolia, Great-leaved Magnolia, Large-leaved Cucumber Tree.

More about bigleaf magnolia

About Bigleaf Magnolia

Magnolia macrophylla · also called Bigleaf Magnolia, Great-leaved Magnolia · flowering

Bigleaf Magnolia holds the record for the largest simple leaf and largest flower of any North American native tree. Its silver-backed leaves can reach 75 cm (30 in) long, and creamy-white flowers measure up to 35 cm (14 in) across. Plant in rich, moist, sheltered soil out of wind; an extraordinary specimen tree for large gardens.

Mature size: 9–15 m tall (30–50 ft) with a crown spread of 4–6 m; leaves up to 75 cm (30 in) long

Watch for — Transplant stress: Fleshy, brittle roots make transplanting difficult; it is best moved only in spring as a small container-grown specimen. Staking for the first two years and generous establishment watering reduce losses.

How to tell bigleaf magnolia needs repotting

Repotting on a calendar is less reliable than reading the plant. For bigleaf magnolia, 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 bigleaf magnolia 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 bigleaf magnolia

Every 2–3 years; top-dress in the in-between years. Bigleaf Magnolia's growth habit — deciduous tree with a straight central trunk and broadly rounded open crown; growth rate of 30–60 cm (1–2 ft) per year when young — sets the pace. Bigleaf Magnolia holds the record for the largest simple leaf and largest flower of any North American native tree. Its silver-backed leaves can reach 75 cm (30 in) long, and creamy-white flowers measure up to 35 cm (14 in) across. Plant in rich, moist, sheltered soil out of wind; an extraordinary specimen tree for large gardens.

What size pot to step bigleaf magnolia up to

Move up exactly one pot size. A heavy bigleaf magnolia 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 bigleaf magnolia

Early spring, just as new growth restarts, is the ideal window for bigleaf magnolia. 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 magnolia

Consider top-dressing first. If bigleaf magnolia 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 rich, moist, well-drained loam; acidic to neutral 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 bigleaf magnolia in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave bigleaf magnolia 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 bigleaf magnolia

Bigleaf Magnolia wants rich, moist, well-drained loam; acidic to neutral. Prefers deep, organically rich, slightly acidic soil (pH 5.5–6.5). Tolerates clay loam and sandy soils with amendment. Sensitive to urban pollution, road salt, and compacted soils. 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 magnolia — frequently asked questions

How often should you repot bigleaf magnolia?

Every 2–3 years; top-dress in the in-between years for bigleaf magnolia. Fully repot bigleaf magnolia 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 rich, moist, well-drained loam; acidic to neutral. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does bigleaf magnolia need?

When is the best time of year to repot bigleaf magnolia?

Should you top-dress or fully repot bigleaf magnolia?

For a big, heavy bigleaf magnolia, 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 bigleaf magnolia after repotting?

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