Heliotrope is a relatively common outdoor bedding plant, where they are used as annuals throughout much of the temperate gardening world. They can, however, be brought indoors and grown as houseplants, where their purple flowers provide a splash of summer color and their scented flowers are reminiscent of vanilla. In recent years, as the plant gained popularity for outdoor gardeners, breeders have introduced new varieties with different color flowers, but the purple heliotrope remains the standard. In terms of growing indoors, these are relatively easy plants to keep for a summer growing season and enjoy the flowers from mid-summer to fall. Overwintering them, however, can be a bit trickier, as the plants are native to warmer regions and will quickly drop leaves if the humidity falls too low (even though they can tolerate slightly colder temperatures).
- Light: Heliotrope prefer full sun to bloom their best. Plants that are light deprived will bloom less vigorously and stretch out from their normal compact, shrubby growth habit.
- Water: Heliotrope like a steady supply of water, but do not want to be drenched. Don't let the plants dry out during the growing season. During winter, provide as much ambient humidity as possible—plants kept at 30 percent humidity, which is typical in a heated winter home, will suffer.
- Soil: Use a fast-draining potting soil with plenty of organic material.
- Fertilizer: Feed with a weak liquid fertilizer throughout the growing season.
Heliotrope are commonly bought as bedding plants, which is probably the best way to start. They can also be grown from seed but will require bottom heating. Sow seeds in the spring for best results. You can also take cuttings from a mother plant and place them into warm, sterile seedling soil. It's best to take cuttings in the spring when new growth is emerging and the summer growing season is beginning.
Heliotrope are naturally compact, shrubby plants with a moderate growth rate. They should only need repotting annually or every other year, depending on the size of the initial pot and the plant's growth rate. Only repot in spring, after the weather warms up and the plant is beginning to grow again. Avoid disturbing the pot or roots in the late summer, as the plant can easily be sent into shock and drop its leaves just as it heads into the winter season, a naturally difficult season for heliotrope.
The basic plant is the Heliotropum arborescens. This plant has been crossed with some other species in the genus to create plants with smaller or larger growth habits, or different flower colors, but for the most part, you will find them simply labeled "Heliotrope" with a varietal name. Choose the variety based on the flower color and growth habit. Heliotrope are bred for stronger scent and more vigorous growth.
Like many flowering plants, heliotrope appreciate the removal of dead and brown flowers to encourage better blooming. If you're buying a plant early in the season, you can also encourage bushier growth and more flowering sites by gently pruning the young plant when you get it home. In general, heliotrope should not be terribly difficult: give them steady and ample water, lots of sunlight, and a regular amount of fertilizer and they will reward you. It can be difficult to overwinter these plants, but since they are relatively common and inexpensive, it might make just as much sense to buy new ones every year. Heliotrope are vulnerable to pests including aphids, mealy bugs, scale, and whitefly. If possible, identify the infestation as early as possible and treat with the least toxic option.