Repotting guide

When & how to repot Square-stemmed Pelargonium (Pelargonium tetragonum)

Also called Square-stemmed Pelargonium, Cactus Geranium, Square-stemmed Geranium.

More about square-stemmed pelargonium

About Square-stemmed Pelargonium

Pelargonium tetragonum · also called Square-stemmed Pelargonium, Cactus Geranium · flowering

Pelargonium tetragonum is an unusual succulent-stemmed species from the Western Cape and Eastern Cape of South Africa, immediately distinctive for its four-angled (square), jointed, pale green semi-succulent stems with small, deciduous or semi-deciduous leaves borne only at the joints. It produces cream to pale pink flowers with dark-pink veining in spring and summer. This architectural curiosity wants excellent drainage, a dry winter rest, and bright sun; it is highly intolerant of overwatering, especially when leafless. Toxic to cats and dogs.

Mature size: 30-60 cm tall and wide; stems can sprawl or be trained upright on a support

How to tell square-stemmed pelargonium needs repotting

Repotting on a calendar is less reliable than reading the plant. For square-stemmed pelargonium, 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 square-stemmed pelargonium

Every 2–3 years, into bone-dry mix. Square-stemmed Pelargonium's growth habit — scrambling, semi-succulent shrublet with distinctive four-angled jointed stems; leaves are small and often absent in winter, giving it a cactus-like silhouette. — sets the pace. Pelargonium tetragonum is an unusual succulent-stemmed species from the Western Cape and Eastern Cape of South Africa, immediately distinctive for its four-angled (square), jointed, pale green semi-succulent stems with small, deciduous or semi-deciduous leaves borne only at the joints. It produces cream to pale pink flowers with dark-pink veining in spring and summer. This architectural curiosity wants excellent drainage, a dry winter rest, and bright sun; it is highly intolerant of overwatering, especially when leafless. Toxic to cats and dogs.

What size pot to step square-stemmed pelargonium up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Square-stemmed Pelargonium 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 square-stemmed pelargonium

Spring or summer, while square-stemmed pelargonium 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 square-stemmed pelargonium

Repot dry. Do not water square-stemmed pelargonium 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 very gritty, fast-draining cactus or succulent compost, ph 6.0-7.0 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 square-stemmed pelargonium 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 square-stemmed pelargonium 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 square-stemmed pelargonium

Square-stemmed Pelargonium wants very gritty, fast-draining cactus or succulent compost, ph 6.0-7.0. Use a cactus compost or a 1:1 mix of loam-based compost and coarse grit or perlite; this species must never sit in moisture-retentive growing medium as the semi-succulent stems rot quickly in wet conditions. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting square-stemmed pelargonium — frequently asked questions

How often should you repot square-stemmed pelargonium?

Every 2–3 years, into bone-dry mix for square-stemmed pelargonium. Repot square-stemmed pelargonium every 2–3 years into a snug pot of very gritty, fast-draining cactus or succulent compost, ph 6.0-7.0, 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 square-stemmed pelargonium need?

When is the best time of year to repot square-stemmed pelargonium?

Should you water square-stemmed pelargonium after repotting?

No — not straight away. Repot square-stemmed pelargonium 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 square-stemmed pelargonium after repotting?

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