Heavenly Blue grows easily from seed if it gets warmth at the start and full sun afterwards. In a climate with frost, such as the UK or the Netherlands, you sow it indoors in spring, plant it out once the last frost has passed and expect the first flowers in mid to late summer. The vine dies with the first frost in autumn.
The calendar in short
| Month | What to do |
|---|---|
| Late April to May | sow indoors in small pots, after nicking or soaking the seed |
| Late May to June | harden off and plant out once the risk of frost has passed |
| June to August | tie in young shoots, water in dry spells |
| July to October | flowers every morning until the first frost |
The months are for a temperate north-west European garden. In a warmer climate everything moves earlier; sowing directly outside works where the soil is warm a week or two after the last frost.
Getting the seed to germinate
Morning glory seed has a hard coat that keeps water out. North Carolina State Extension advises to "nick the hard seed coat and soak overnight before planting" (NC State Extension). The RHS gives the same advice for all tough-coated seed: pre-soak, scrape or nick it with sandpaper or a knife to raise the chance of germination (RHS: how to sow seeds indoors).
- Nick the pointed end of the seed coat with nail clippers or a knife, or rub it on sandpaper until the pale inside just shows (Johnny's Selected Seeds).
- Or soak the seeds overnight in lukewarm water. Seeds that have swollen are ready; sow them straight away.
- Sow one or two seeds per small pot, about 6 mm deep, in ordinary seed compost, three to four weeks before you plan to plant out (Johnny's).
- Keep the pots warm. Most seed needs around 18 °C to germinate (RHS), and morning glory does best a little warmer.
Wash your hands after handling the seed. The RHS lists the plant as harmful if eaten and advises gloves when handling it (RHS).
Planting out
'Heavenly Blue' has the RHS hardiness rating H1C, which means it needs frost-free conditions to survive (RHS). Harden the young plants off for a week or two by putting them outside during the day, then plant them out when nights are reliably mild.
- Sun. Full sun, ideally against a south or west-facing wall or fence, sheltered from cold wind (RHS).
- Soil. Moist but well-drained. The plant does not tolerate standing water, and it flowers in poor soil with little or no fertiliser (NC State Extension).
- Containers. A large pot with a wigwam of canes works on a balcony or patio. Water it often in summer.
Support
The vine climbs by twining. It needs something thin to wind around: canes, string, wire or netting. A flat wall or a thick post gives it no grip. Expect 2.5 to 4 m of growth in one season (RHS), so give it the height from the start, and guide the first shoots onto the support by hand.
Why it is not flowering yet
Heavenly Blue is slow to flower compared with many summer annuals. A seed company that grows it for sale gives 110 to 120 days from sowing to flower and notes that the plant needs short days and long nights to trigger flowering (Johnny's Selected Seeds). In northern Europe that means the main show often comes from August onwards, as days shorten. Early-flowering selections were already sold in the 1940s for exactly this reason (see the plant).
Too little sun and a cold start delay flowering further.
Seed at the end of the season
After each flower fades, a round capsule forms with a few black, angular seeds inside. They are ripe when the capsule is dry and papery. In a mild climate the plant can seed itself: Illinois Extension notes that it "will reseed heavily" (University of Illinois Extension). In parts of the US the species is treated as a weed; Arizona lists Ipomoea tricolor, there called grannyvine, as a Class C noxious weed (University of Arizona Extension). In a cold north-European winter self-sown seedlings are less of an issue, but it is good practice to pick off ripening capsules near borders and fields.
If you save seed to sow next year, label the jar clearly, store it dry and out of reach, and never keep it with food. The reasons are on the risks page.
Children and pets
All parts of the plant contain alkaloids, the seeds most of all. The ASPCA lists morning glory as toxic to dogs, cats and horses, with vomiting as the main sign and hallucinations possible after large amounts of seed (ASPCA). Grow it out of reach of small children and animals that chew plants, and contact a doctor, a poison centre or a vet if seeds have been swallowed.
Read on
- Risks of the seeds, including treated seed
- The plant and the cultivar
- Legal status of the seeds per country