Repotting guide

When & how to repot Japanese morning glory (Ipomoea nil)

Also called Japanese morning glory, Picotee morning glory, Asagao.

More about japanese morning glory

About Japanese morning glory

Ipomoea nil · also called Japanese morning glory, Picotee morning glory · flowering

Ipomoea nil — known in Japan as Asagao — is an Asian morning glory species with extraordinary flower diversity, from pure white to striped, picotee, and deeply fringed forms. A fast-climbing annual grown for ornamental displays on fences, obelisks, and balcony railings. Thrives in warm summers with full sun and lean soil.

Mature size: 1.5–3 m tall in a single growing season, depending on support and conditions.

Watch for — Transplant shock and wilting: Morning glories have sensitive taproots and dislike transplanting. Always sow into individual biodegradable pots or cells and transplant pot-and-all to avoid root disturbance. Wilting at transplant is common; shade briefly and water in well.

How to tell japanese morning glory needs repotting

Repotting on a calendar is less reliable than reading the plant. For japanese morning glory, 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 japanese morning glory 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 japanese morning glory

Pot on seedlings as they grow; not a perennial repot. Japanese morning gloryis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Vigorous twining annual climber; fast-growing in warm conditions, easily reaching its support within weeks of germination. Flower forms are exceptionally diverse — the Asagao tradition includes thousands of cultivated forms..

What size pot to step japanese morning glory up to

Pot japanese morning glory 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 japanese morning glory

Pot japanese morning glory 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 japanese morning glory

Pot on before it is root-bound. Check japanese morning glory 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 average to moderately fertile, well-drained loam 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 japanese morning glory 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 japanese morning glory

Japanese morning glory wants average to moderately fertile, well-drained loam. Ipomoea nil adapts to ordinary garden soil (pH 6.0–7.0). Avoid excessively rich soils — moderate fertility encourages balanced leaf and flower development. In containers, use a peat-free multi-purpose compost with added perlite for drainage. Good drainage is essential. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting japanese morning glory — frequently asked questions

How often should you repot japanese morning glory?

Pot on seedlings as they grow; not a perennial repot for japanese morning glory. Japanese morning glory is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into average to moderately fertile, well-drained loam 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 japanese morning glory need?

When is the best time of year to repot japanese morning glory?

Can you put japanese morning glory straight into a much bigger pot?

No. Even a fast-growing japanese morning glory 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 japanese morning glory after repotting?

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