Hardy gloxinia (Incarvillea delavayi) is also known as Chinese trumpet flower. It is from Southwestern China. The scientific name for this species, delavayi, is after an 18th century Jesuit monk who first described the plant scientifically.
This plant has short, deeply divided, fernlike green leaves and pink trumpet shaped flowers with a yellow throat. The flowers grow on tall stalks. They bloom from late spring through late summer if deadheaded regularly. These flowers are good for color accents in flower beds, borders, or in rock gardens. Because the large tap root needs good drainage, hardy gloxinia grows best in raised beds or rock gardens.
Hardy gloxinia grows in zones 5-7. Some literature says they will also grow in zones 8-10, but they are not tolerant of the extreme heat of the summers in those zones. While hardy gloxinia should be planted in full sun in zones 5-7, it should be planted in a place that has afternoon shade in zones 8-10.
Hardy gloxinia is a perennial. It may be grown as an annual in zones where the winters are too cold for the plants to survive.
Till the ground to a depth of six inches and add three inches of compost. This should provide the drainage and room for the tap root this plant requires. Plants can be grown from seed or from crowns. If you grow from crowns, plant the crown six inches under the soil and cover. Plant the crowns twenty-four inches apart as the plants can be 12-18 inches tall and 16-18 inches wide. Pleant after all danger of frost has passed. Water in. Water consistently during the growing season, keeping the soil moist but never soaked. In the winter, water sparingly.
To grow from seed, sprinkle the seed on the ground where you want the plants to grow in the autumn or the spring. The seed needs light to germinate so do not cover it with soil. Germination takes 25-30 days. As the seeds start to grow, thin as needed. Seeds will bloom the following year if planted in the spring.
To maintain these delicate plants, mulch the crowns in the winter. Remove the mulch after all danger of frost is past. The plants are relatively late to emerge after the winter, and the crowns are very delicate, so mark where you plant them. Water regularly during the growing season as these plants are from areas that receive regular rain. Fertilize monthly while blooming with a balanced fertilizer.
Hardy gloxinia are self seeding, so if you do not want them to spread, remove the seed heads before they open. Eventually, the plants will divide enough that they become too crowded. When that happens, you carefully divide the plants in the spring after they bloom. Make sure you get all of the taproot when you dig up the plants to divide them. The tap roots can make division difficult because they are so long.
Hardy gloxinia are vulnerable to snails and slugs. Otherwise, they are fairly pest free.