Repotting guide

When & how to repot Grandidier's Uncarina (Uncarina grandidieri)

Also called Grandidier's Uncarina, Sesame Tree, Madagascan Unicorn Plant.

More about grandidier's uncarina

About Grandidier's Uncarina

Uncarina grandidieri · also called Grandidier's Uncarina, Sesame Tree · tropical

Uncarina grandidieri is a striking deciduous succulent tree from Madagascar's dry spiny thickets, grown for its swollen pachycaul trunk and showy yellow flowers. It demands full sun, excellent drainage, and a dry winter rest. A rewarding specimen for collectors of Madagascan flora and arid-climate enthusiasts.

Mature size: 1.5–3 m tall in cultivation; to 5 m in habitat

Watch for — Root and caudex rot: The most common cause of death in cultivation — almost always due to watering during dormancy or poorly drained soil. Ensure complete dryness from October to March and use a very gritty substrate.

How to tell grandidier's uncarina needs repotting

Repotting on a calendar is less reliable than reading the plant. For grandidier's uncarina, watch for these signs:

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

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 grandidier's uncarina

Every 2–3 years, into bone-dry mix. Grandidier's Uncarina's growth habit — deciduous pachycaul shrub or small tree with a greatly swollen water-storing trunk (caudex), sparse succulent branches, and large yellow trumpet flowers appearing before or with new leaves. — sets the pace. Uncarina grandidieri is a striking deciduous succulent tree from Madagascar's dry spiny thickets, grown for its swollen pachycaul trunk and showy yellow flowers. It demands full sun, excellent drainage, and a dry winter rest. A rewarding specimen for collectors of Madagascan flora and arid-climate enthusiasts.

What size pot to step grandidier's uncarina up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Grandidier's Uncarina stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

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 grandidier's uncarina

Spring or summer, while grandidier's uncarina is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting grandidier's uncarina

Repot dry. Do not water grandidier's uncarina for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty gritty, fast-draining succulent mix ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set grandidier's uncarina at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep grandidier's uncarina completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for grandidier's uncarina

Grandidier's Uncarina wants gritty, fast-draining succulent mix. Use a 50:50 blend of horticultural grit or coarse perlite with loam-based compost. Avoid peat, which retains moisture and promotes root rot. Terracotta pots are strongly preferred for their breathability. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting grandidier's uncarina — frequently asked questions

How often should you repot grandidier's uncarina?

Every 2–3 years, into bone-dry mix for grandidier's uncarina. Repot grandidier's uncarina every 2–3 years into a snug pot of gritty, fast-draining succulent mix, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does grandidier's uncarina need?

When is the best time of year to repot grandidier's uncarina?

Should you water grandidier's uncarina after repotting?

No — not straight away. Repot grandidier's uncarina into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise grandidier's uncarina after repotting?

Not immediately. Wait about 3 weeks after repotting grandidier's uncarina. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.