The Japanese morning glory (Ipomoea nil, synonym Pharbitis nil), called asagao in Japan, is an annual twining vine in the bindweed family. It is grown from seed for its large funnel-shaped flowers, which open in the morning. Japanese gardeners have bred it for centuries, which is why it comes in so many flower colors, patterns and leaf shapes. Japanese morning glory care is the same as for other annual morning glories: nick and soak the hard seeds, sow in warm soil after frost, give full sun and a support to climb, and go easy on fertilizer. This guide follows Iowa State, University of Illinois and NC State Extension, the RHS, the ASPCA and published research.
| Need | What the sources say |
|---|---|
| Seed prep | Nick the seed coat (Iowa State); soak 24 hours (Illinois, Iowa State) |
| Sowing | Indoors or direct outdoors (Illinois); outdoors after frost in warm soil |
| Light | Full sun, 6 or more hours (NC State, Illinois) |
| Soil | Moderately fertile, moist but well-drained (NC State); low fertility (Illinois) |
| Habit | Annual twining vine (RHS); reseeds heavily (Illinois) |
| Pests | Aphids, spider mites; powdery mildew, root rot (NC State, for I. purpurea) |
| Pets | Morning glories toxic to dogs, cats and horses (ASPCA) |
Sources: Iowa State Extension; University of Illinois Extension; NC State Extension (Ipomoea purpurea); RHS; ASPCA.
What Is Japanese Morning Glory?
The RHS lists Ipomoea nil as Japanese morning glory, with the synonym Pharbitis nil, in the family Convolvulaceae. It is a different species from the common morning glory (I. purpurea) and the ‘Heavenly Blue’ type (I. tricolor), though all three are grown the same way.
A 2018 review by Morita and Hoshino says I. nil has been a floricultural plant in Japan since the 17th-century Edo period. The wild type has blue flowers, and spontaneous mutants with other colors and patterns have been collected and kept since then. A 2016 genome study by Hoshino and colleagues in Nature Communications notes that the species is used as a model plant for floricultural traits, with over 1,500 mutant lines, and that a family of transposons (Tpn1) is the major source of its mutations. That is where its unusual flower patterns and leaf shapes come from.
Japanese Morning Glory Seeds: Nicking and Soaking
Morning glory seeds have a hard coat that slows water uptake. Iowa State Extension says morning glories germinate faster and more uniformly if the seed coat is nicked slightly, for example by snipping a small piece off one end with a nail clipper, and suggests soaking scarified seeds in warm water for 24 hours before sowing. Illinois Extension says seeds germinate quickly if soaked for 24 hours before planting.
- Nick or file a small spot on the seed coat, away from the scar where the seed was attached, just enough to break the hard outer layer.
- Soak in warm water for up to 24 hours. Seeds that have swollen are ready to sow.
- Sow promptly, about a quarter to half an inch deep, in moist, warm soil or seed compost.
Sowing, Sun and Soil
Illinois says morning glories can be started indoors or sown directly in the garden. They are frost-tender, so sow outdoors only after the last frost when the soil has warmed. If you start them indoors, sow a few weeks before the last frost in individual pots so you can plant them out without disturbing the roots much.
Light: full sun, 6 or more hours of direct sun (NC State, Illinois). Flowers open in the morning, so a spot with morning sun shows them off best.
Soil: NC State says common morning glory grows in most moderately fertile, moist but well-drained soils, and Illinois recommends soil where fertility is kept to a minimum. Rich soil is not needed; heavy, waterlogged soil invites root rot (NC State).
Pinching for More Branches
Pinching out the growing tip of a young plant, after it has a few true leaves, encourages side shoots, so you get a bushier plant with more stems to carry flowers. Use clean fingers or scissors, and tie the side shoots to the support as they grow.
Supports and Pots
As a twining vine, Japanese morning glory needs something to climb: a trellis, netting, strings or an obelisk. A traditional Japanese style trains potted asagao on a small lantern-shaped frame (andon), which keeps the plant compact and portable. Any pot needs drainage holes and a well-drained potting mix, and potted plants need more frequent watering than plants in the ground. Illinois notes that morning glories quickly cover structures.
Watering and Feeding
Water during dry spells, especially plants in pots, but don’t keep the soil soggy. For feeding, the sources point the same way: NC State says moderately fertile soil, and Illinois says keep fertility to a minimum. Lots of lush leaves and few flowers is a sign of too much fertilizer, especially nitrogen, so skip rich feeds.
Saving Seed and Preventing Self-Seeding
Illinois says morning glories reseed heavily, and NC State tags common morning glory as self-seeding and weedy. To prevent unwanted seedlings, remove spent flowers before the seed pods ripen.
To save seed, let a few pods ripen and dry on the vine until they turn brown and papery, then collect them into a paper bag and store the dry seeds in a cool, dry place. Seeds from different varieties grown together may not come true. Label them and keep them away from children and pets (see below).
Problems and Pests
| Problem | Likely cause | What to do |
|---|---|---|
| Seeds don’t come up | Hard seed coat not nicked or soaked; cold, wet soil | Nick and soak; sow in warm soil after frost |
| Lots of leaves, few flowers | Too much fertilizer; too little sun | Stop feeding; give 6+ hours of sun |
| Sticky leaves, curled tips | Aphids | Rinse off; see our aphid guide |
| Fine stippling, webbing | Spider mites, often in hot, dry weather | Rinse undersides; see our spider mite guide |
| White powdery coating | Powdery mildew | Improve air flow; remove badly affected leaves |
| Wilting with wet soil | Root rot | Improve drainage; water less |
Pests and diseases listed by NC State Extension for Ipomoea purpurea.
See our aphid guide and spider mite guide.
Is Japanese Morning Glory Poisonous?
Yes, mainly the seeds. The ASPCA lists morning glories (Ipomoea species) as toxic to dogs, cats and horses. Its listed toxic principles are indole alkaloids (lysergic acid, lysergamide, elymoclavine and chanoclavine), and the signs are vomiting, with large amounts of seeds possibly causing hallucinations. NC State gives the same warning about the seeds of common morning glory. Keep seeds and pods away from children and pets, and call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 if a pet eats them. See our cat-safe plants list.
For more garden flowers, see our guides to forget-me-nots and monkshood.
Frequently Asked Questions
Why aren’t my Japanese morning glory seeds germinating?
Usually because the hard seed coat wasn’t nicked or the soil was too cold. Iowa State says nicking helps seeds germinate faster and more evenly, and Illinois suggests a 24-hour soak.
What is the difference between Ipomoea nil and common morning glory?
They are different species in the same genus: Japanese morning glory is I. nil and common morning glory is I. purpurea. I. nil has been bred in Japan since the Edo period and has many flower and leaf mutants (Morita and Hoshino 2018).
Can Japanese morning glory grow in pots?
Yes. Use a pot with drainage holes, a well-drained mix, a small frame or trellis, and full sun, and water more often than plants in the ground.
Is Japanese morning glory invasive?
Morning glories reseed heavily (Illinois), and NC State calls common morning glory weedy. Deadhead before seed pods ripen if self-seeding is a concern where you live.
Is Japanese morning glory poisonous to cats and dogs?
Yes. The ASPCA lists morning glories as toxic to dogs, cats and horses, mainly because of alkaloids in the seeds.
Is Japanese morning glory annual or perennial?
It is grown as an annual from seed each year, and the RHS lists it with the annual and perennial twining Ipomoea. It is killed by frost.
Sources
- RHS: Ipomoea nil (Japanese morning glory)
- Iowa State University Extension: Direct Seeding Vegetables and Annuals
- University of Illinois Extension: Morning Glory
- NC State Extension Plant Toolbox: Ipomoea purpurea
- Morita, Y. and Hoshino, A. (2018). Recent advances in flower color variation and patterning of Japanese morning glory and petunia. Breeding Science 68
- Hoshino, A. et al. (2016). Genome sequence and analysis of the Japanese morning glory Ipomoea nil. Nature Communications 7
- ASPCA: Morning Glory