Give me an easy-care plant that flowers nonstop and offers a hauntingly beautiful fragrance, and I'm in paradise. Common heliotrope (Heliotropium arborescens) is a fragrant, woody perennial, native to South America. It was introduced into greenhouse culture in Europe in 1757 after travellers discovered it in Peru. Hence, it's sometimes listed and sold as H. peruvianum.
By the nineteenth century, heliotrope was used extensively for bedding plants and as standards. It was nicknamed the "cherry pie plant" because its fragrance supposedly resembles the aroma of a freshly baked cherry pie. A few species are so fragrant that they are grown in Europe to make perfume.
According to Mary Cashman, a garden specialist with White Flower Farm in Litchfield, Connecticut, heliotrope is an underused plant that's easy to care for and does well in most parts of the country except the Deep South, where high humidity limits best growth.
A member of the borage family, common heliotrope is one of about 250 Heliotropium species, but it is the only one widely grown in gardens. All are tropical or subtropical shrubs or subshrubs (a somewhat woody plant sometimes grown and used as a shrub or perennial).
Common heliotrope grows 2 to 3 feet high; some varieties are a compact 10 inches. Tiny, star-shaped flowers of deep blue, purple, lavender, or white come in tightly packed spikes that develop into rounded, 2- to 4-inch-diameter clusters. Hairy and veined 1- to 3-inch leaves have a purplish cast. All parts of the plant are toxic.
Common heliotrope is often prized for its fragrance, but sometimes only for its color. My garden contains a white heliotrope variety (H. arborescens 'Alba') an old-fashioned variety graced with the enticing scent of vanilla. In my area of southern California (USDA Hardiness Zone 10), it flowers every month of the year. But the scent of the deep blue 'Marine', for example, is less heady than that of 'Alba'.
Here are brief descriptions of some of the varieties currently available in the United States as seeds (S) or plants (P).
'Alba' (P): strong vanilla scent; white; 2 to 3 feet.
'Fragrant Delight' (S): vanilla scent; royal purple fading to lavender; 15 to 18 inches.
'Iowa' (P): sweet, slightly winelike fragrance; deep purple; dark green leaves with a purple cast; 2 to 3 feet.
'Dwarf Marine' (S,P): scant fragrance; intense blue; bushy, compact dwarf, 10 inches.
Don't confuse common heliotrope (H. arborescens) with so-called garden heliotrope (Valeriana officinalis), a perennial herb with tiny fragrant flowers in clusters above low-growing leaves and bad-smelling roots. The latter can become invasive.
Start from plants or seeds. Both are more readily available by mail order than at retail nurseries. After frost danger has passed, set out seedlings or plants in well-drained soil in full sun. If you live in a region that experiences hot summers, grow heliotrope in a partially shaded site.
Growing from seed. Start seeds indoors 10 to 12 weeks before the average last frost in your area. Use a planting mixture of 3 parts commercial potting mix to 1 part sand. Cover the seeds with 1/4 inch of soil, and keep the seedbed moist but not soggy. Seeds germinate in about two weeks at 70° to 80° F. As seedlings mature, thin them out, and pinch back the tips to keep the plants bushy. Feed after 6 weeks. You can also sow seeds directly in decorative containers or in flats or trays in preparation for landscape use.
Container culture. Two of the best ways to grow heliotrope are in a hanging basket (particularly 'Marine') and as a standard. Either method is ideal, because the flowers are easier to smell up close. Heliotrope is never invasive, so it can be grown in patio containers where vinca, dusty miller, or marigolds make attractive companions for its delicate flowers.
Common heliotrope is a tender perennial. In a pot in a northern garden, the plant is only hardy to about 40° F. With its roots in open soil in a southern garden, temperatures at or below freezing will kill or damage leaves but not harm the roots. If you live where winter temperatures regularly fall (and hold) below 32° F, such as zone 9b and colder, treat heliotrope as you would an annual: Plant heliotrope outdoors after frost danger passes and let it die in the fall. Alternatively, bring the plant back inside to grow as a houseplant, or root a few cuttings to start new plants indoors over the winter.
In zones 10 and 11, treat it like any other perennial: Rejuvenate by cutting back old growth (but not as far as the woody stems) before growth begins in late winter or early spring.
An easy way to overwinter desirable varieties is to root cuttings in the fall. Use a soilless mix recommended for germinating seeds (see potting mix information in the section on growing heliotrope from seed above), and keep plants indoors in bright, indirect light; roots will develop within a month. Keep the plant going near a bright window or under fluorescent lights until spring. Set out when danger of frost has passed.
Overwinter container plants by bringing them indoors when frost is likely. Give them moist air, direct sun, and cool nights (50° to 55° F).
Fertilize plants growing in containers every 2 weeks with a liquid fertilizer according to the label directions. Feed plants growing in the ground more sparingly. Use the same liquid fertilizer, but monthly, or mulch the plant with homemade or commercial compost once or twice a season. Excessively rich soil fosters leggy, less attractive growth and leaves plants more prone to pests.
Plants are rarely susceptible to insects or diseases, although spider mites may attack plants growing indoors. Control mites with sprays of water or insecticidal soap. Soggy soil, whether in the garden or indoors, will cause the leaves to brown and drop off. Still, the plant will recover quickly as soon as good drainage and aeration return.