Heavenly Blue is a cultivar of Ipomoea tricolor Cav., a twining climber in the bindweed family (Convolvulaceae) that is native to Mexico. The Spanish botanist Antonio José Cavanilles described the species in the 1790s in the third volume of his Icones et descriptiones plantarum (IPNI). In its home range it is a short-lived perennial; in gardens with frost it is grown as an annual and dies with the first cold night (NC State Extension).
What the plant looks like
The Royal Horticultural Society describes the cultivar as "a twining annual with heart-shaped leaves and funnel-shaped, deep sky-blue flowers to 8cm across, with white throats" (RHS). The stems twine around canes, wires and netting and reach 2.5 to 4 m in a single season. The RHS gives 'Heavenly Blue' its Award of Garden Merit, a mark for plants that perform reliably in British gardens.
| Feature | 'Heavenly Blue' |
|---|---|
| Habit | twining climber, grown as an annual |
| Leaves | heart-shaped |
| Flowers | funnel-shaped, sky blue with a white to pale yellow throat, up to 8 cm |
| Height | 2.5 to 4 m in one season |
| Hardiness | RHS H1C: needs frost-free conditions |
| Native range of the species | central and southern Mexico |
Sources: RHS, NC State Extension.
A flower that lasts one morning
Each flower opens in the early morning and fades by evening (University of Illinois Extension). The plant makes up for it in numbers. Dreer's 1943 seed catalogue promised a vine "covered with rich sky blue flowers from late summer until frost" (Dreer's Garden Book 1943).
The blue itself is a small piece of chemistry. The buds are purplish red. As a flower opens, the cells of the petal pump hydrogen ions out of the vacuole, the compartment where the pigment is stored, and the pH there rises from about 6.6 to 7.7. The same anthocyanin pigment then appears blue instead of red. Japanese researchers worked this out on 'Heavenly Blue' itself and traced it largely to an ion exchanger in the petal cells (Yoshida et al., 2009; Yoshida et al., 2005).
Tricolor or violacea
Older books, and much of the 1960s literature about the seeds, call this plant Ipomoea violacea. In 1963 the Harvard ethnobotanist Richard Evans Schultes wrote that I. tricolor and I. violacea "refer to one polymorphic species" and preferred the older name I. violacea (Wasson, 1963, with a note by Schultes). Current databases keep them apart: GBIF accepts I. tricolor Cav. and keeps I. violacea L. as a separate species, while an I. violacea published by Lunan is listed as a synonym of I. tricolor (GBIF species 2928589, checked 10 October 2026).
This matters for two reasons. Chemical papers about "Ipomoea violacea" seeds from Mexico are usually about the plant now called I. tricolor. And some laws still use the old name: Louisiana's statute names Ipomoea violacea only (see legal status).
The common morning glory of North American fields and fences, Ipomoea purpurea, is a different species. Seed of it is sometimes sold under the name Heavenly Blue. In a Polish laboratory study, two packets of I. purpurea seed contained no ergot alkaloids at all, while every packet labelled Heavenly Blue did (Nowak et al., 2016).
Where the cultivar comes from
The early history of 'Heavenly Blue' is poorly documented. Seed-trade histories tell of an early-flowering strain selected by a gardener named Clarke and sold in the 1930s, but we could not trace that story to a primary source, so we do not repeat its details here.
What can be checked is the seed catalogues. In its 1943 Garden Book, the Philadelphia seed house Henry A. Dreer offered "Heavenly Blue, Improved Early-Flowering" and wrote that "no other climber enjoys such widespread popularity as this early-flowering Morning Glory", with sky-blue flowers about 11 cm across and a white throat (Dreer's Garden Book 1943). The same catalogue offered 'Pearly Gates', a white morning glory "as large as those of Heavenly Blue", which had received a silver medal in the 1942 All-America Selections. By then 'Heavenly Blue' was the standard against which new morning glories were measured.
Other cultivars of I. tricolor include 'Pearly Gates' and 'Flying Saucers'. A 2025 study found the same symbiotic fungus in seed of all three (see what is in the seeds).
Related plants
Several other plants in the same family are known for ergoline alkaloids in their seeds, among them Turbina corymbosa, the source of the seeds called ololiuqui in Mexico (see history), and Hawaiian baby woodrose (Argyreia nervosa), a woody vine from South Asia. This site is about the garden morning glory only.