Petunia axillaris aka Garden Petunia

Petunia axillaris typically reaches 12-24 inches (30-60 cm) in both height and spread, though some specimens can grow up to 4 feet tall in ideal conditions. The plant has a vigorous, gently mounding growth habit that produces abundant blooms throughout the growing season. Growth rate is moderate and influenced by factors such as light availability, water consistency, and soil fertility.

Petunia axillaris thrives in nighttime temperatures between 57-65°F (14-18°C) and daytime temperatures between 61-85°F (16-29°C). The plant tolerates heat well, flourishing up to 100°F (38°C), but is frost-sensitive and damaged at 32°F (0°C). Plant outdoors only after soil warms to at least 60°F (16°C) and all danger of frost has passed.

Petunia axillaris produces elegant, trumpet-shaped white flowers that are 3-7 cm (1.2-2.8 inches) long - the only white flowers found in the Petunia genus. The plant blooms profusely from spring through fall, with flowers opening in the evening to release their fragrance. These highly-scented blooms are specifically adapted for pollination by nocturnal hawk moths and emit their strongest fragrance at night.

Yes, Petunia axillaris is highly fragrant with a strong nocturnal scent. The flowers emit large amounts of volatile compounds, particularly benzenoids (benzaldehyde, benzyl alcohol, and methyl benzoate), in a strict circadian rhythm that peaks at night. This evening fragrance is specifically adapted to attract nocturnal hawk moth pollinators, making the plant an excellent choice for evening gardens.

Petunia axillaris has three recognized subspecies: P. axillaris subsp. axillaris and P. axillaris subsp. parodii (both found in the flat parts of the Pampas), and P. axillaris subsp. subandina (found in highlands near the Andes). Additionally, P. axillaris is one of the two parent species of the commonly-grown garden petunia (Petunia × hybrida), which was created by crossing P. axillaris with P. integrifolia.

Yes, Petunia axillaris is primarily grown outdoors as a bedding plant or in containers. It's hardy as a perennial in USDA zones 9-11 but typically grown as an annual in colder climates. Plant outdoors after the last frost date when soil has warmed to at least 60°F. The plant requires full sun (5-6 hours minimum) and performs best in garden beds, borders, or outdoor containers with good drainage.

Prune Petunia axillaris regularly to maintain its shape and encourage bushier growth. Remove spent flowers (deadheading) to promote continuous blooming throughout the season. Cut back any leggy or damaged stems to encourage more vigorous flowering. Regular pruning helps maintain a compact, attractive form and can extend the blooming period, though some modern varieties are self-cleaning and require less deadheading.

Since Petunia axillaris is typically grown as an annual, repotting is rarely necessary. However, if growing as a perennial in warm climates (zones 9-11) or starting seeds indoors, transplant seedlings to larger containers as they outgrow their space. Container plants benefit from fresh potting soil at the beginning of each growing season. Ensure containers have good drainage to prevent root rot.

Propagate Petunia axillaris from seeds or cuttings. For seeds, sow indoors 8-10 weeks before the last frost date - seeds need gentle warmth and light (don't cover them) and can be slow to germinate. For cuttings, take 4-6 inch stem cuttings from healthy plants in spring, ensuring at least two sets of leaves. Remove leaves from the bottom 2 inches and plant in well-draining soil mix. Cuttings root readily under warm, humid conditions.

Common pests include aphids (whitefly, greenfly, blackfly), tobacco budworms, and thrips. Aphids are the most frequent problem - they suck sap, causing yellowing and distorted leaves, and can spread viral diseases including deadly mosaic viruses. Control aphids by spraying with water or using horticultural soap. Tobacco budworms damage flower buds. Maintain good air circulation, consistent watering, and avoid drought stress to prevent pest infestations and fungal issues.

Petunia axillaris is primarily pollinated by nocturnal hawk moths, particularly Manduca sexta. The plant's white flowers, long narrow corolla tubes, abundant nectar, and strong nocturnal fragrance are all adaptations for moth pollination. The scent emission timing perfectly matches the moths' nighttime activity. While bees and beetles may visit during the day, hawk moths are the most effective pollinators. This makes P. axillaris valuable for pollinator gardens that support native moth populations.

Plant Petunia axillaris outdoors after the last spring frost when soil reaches 60°F. During summer, maintain regular watering (especially in containers) and fertilize every 2-3 weeks for continuous blooming. In hot weather above 85°F, provide afternoon shade if possible. In zones 9-11, plants may survive winter as short-lived perennials; elsewhere, treat as annuals. Before fall frost, take cuttings if you wish to preserve the plant indoors over winter, though most gardeners simply replant annually.