Repotting guide

When & how to repot Euphorbia mammillaris (Euphorbia mammillaris)

Also called Indian corn cob, corn cob euphorbia.

More about euphorbia mammillaris

About Euphorbia mammillaris

Euphorbia mammillaris · also called Indian corn cob, corn cob euphorbia · houseplant

Euphorbia mammillaris, the corn cob euphorbia, is a clustering South African succulent whose short, ribbed, knobbly cylindrical stems resemble corn cobs, often tinged purple-pink in strong light. A variegated 'Variegata' form is widely grown. It is easy and slow-growing, asking only for bright light, gritty soil, and minimal water.

Mature size: Individual stems reach about 15-20cm tall; clumps spread to 20-30cm or more wide over time.

Watch for — Basal and root rot: Dense clumps trap moisture; overwatering rots the base and lower stems. Use very gritty soil, water only when fully dry, and keep nearly dry in winter.

How to tell euphorbia mammillaris needs repotting

Repotting on a calendar is less reliable than reading the plant. For euphorbia mammillaris, 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 euphorbia mammillaris

Every 2–3 years, into bone-dry mix. Euphorbia mammillaris's growth habit — low, clustering succulent forming dense colonies of short, erect, ribbed cylindrical stems studded with small tubercles and topped with slender spines; spreads by offsets at the base. — sets the pace. Euphorbia mammillaris, the corn cob euphorbia, is a clustering South African succulent whose short, ribbed, knobbly cylindrical stems resemble corn cobs, often tinged purple-pink in strong light. A variegated 'Variegata' form is widely grown. It is easy and slow-growing, asking only for bright light, gritty soil, and minimal water.

What size pot to step euphorbia mammillaris up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Euphorbia mammillaris 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 euphorbia mammillaris

Spring or summer, while euphorbia mammillaris 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 euphorbia mammillaris

Repot dry. Do not water euphorbia mammillaris 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 free-draining cactus and 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 euphorbia mammillaris 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 euphorbia mammillaris 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 euphorbia mammillaris

Euphorbia mammillaris wants free-draining cactus and succulent mix. A gritty cactus compost with added perlite, pumice or coarse sand. Excellent drainage prevents the basal rot to which this clumping species is prone; shallow pots suit its spreading roots. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting euphorbia mammillaris — frequently asked questions

How often should you repot euphorbia mammillaris?

Every 2–3 years, into bone-dry mix for euphorbia mammillaris. Repot euphorbia mammillaris every 2–3 years into a snug pot of free-draining cactus and 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 euphorbia mammillaris need?

When is the best time of year to repot euphorbia mammillaris?

Should you water euphorbia mammillaris after repotting?

No — not straight away. Repot euphorbia mammillaris 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 euphorbia mammillaris after repotting?

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