Repotting guide

When & how to repot Hemp-leaved Marshmallow (Althaea cannabina)

Also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow, Hempweed Mallow.

More about hemp-leaved marshmallow

About Hemp-leaved Marshmallow

Althaea cannabina · also called Hemp-leaved Marshmallow, Cannabis-leaved Marshmallow · herb

Althaea cannabina is a tall, graceful Mediterranean herb with deeply divided, hemp-like leaves and small, delicate pink flowers borne over a long season. Traditionally used in herbalism similarly to common marshmallow (A. officinalis) for its mucilaginous roots and leaves. Drought-tolerant and attractive to pollinators; well-suited to herb gardens and naturalistic borders in warm climates.

Mature size: 100–200 cm tall (3.3–6.5 ft) and 60–90 cm wide

Watch for — Root rot in wet soils: The taproot rots rapidly in waterlogged or poorly draining soils. Plant in raised beds or well-amended ground; do not overwater.

How to tell hemp-leaved marshmallow needs repotting

Repotting on a calendar is less reliable than reading the plant. For hemp-leaved marshmallow, watch for these signs:

Roots circling the bottom of the module or pot, or poking out of the drainage holes.
The seedling dries out within a day and growth has visibly stalled.
Roots are white and matted in a tight spiral when you tip the plant out.
It has outgrown its current container for the stage of the season — pot hemp-leaved marshmallow on before it becomes hard root-bound.

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 hemp-leaved marshmallow

Pot on seedlings as they grow; not a perennial repot. Hemp-leaved Marshmallowis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Tall, branching perennial herb with erect to arching stems and finely dissected, palmate leaves resembling hemp foliage.

What size pot to step hemp-leaved marshmallow up to

Pot hemp-leaved marshmallow on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

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 hemp-leaved marshmallow

Pot hemp-leaved marshmallow on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting hemp-leaved marshmallow

Pot on before it is root-bound. Check hemp-leaved marshmallow regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
Pot into rich mix. Set it into fresh light, well-drained, sandy or loamy soil; alkaline to neutral preferred at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water hemp-leaved marshmallow in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for hemp-leaved marshmallow

Hemp-leaved Marshmallow wants light, well-drained, sandy or loamy soil; alkaline to neutral preferred. Native to dry, stony, calcareous habitats. Prefers poor to moderately fertile, free-draining soil at pH 6.5–8.0. Rich soils promote excessive vegetative growth. Does not tolerate heavy clay or waterlogged 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 hemp-leaved marshmallow — frequently asked questions

How often should you repot hemp-leaved marshmallow?

Pot on seedlings as they grow; not a perennial repot for hemp-leaved marshmallow. Hemp-leaved Marshmallow is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into light, well-drained, sandy or loamy soil; alkaline to neutral preferred so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does hemp-leaved marshmallow need?

When is the best time of year to repot hemp-leaved marshmallow?

Can you put hemp-leaved marshmallow straight into a much bigger pot?

No. Even a fast-growing hemp-leaved marshmallow should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise hemp-leaved marshmallow after repotting?

Not immediately. Wait about 1 week after repotting hemp-leaved marshmallow. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.