How to Grow and Care for Lobelia

closeup of lobelia

The Spruce / Evgeniya Vlasova

In This Article

Lobelia (Lobelia erinus) is a tender perennial widely grown as an annual plant in most USDA zones. It is commonly sold in the annuals section of the nursery and has a wide variety of uses in the garden: plant it in a container, use it to edge the front of your borders, or let it spill over the sides of a hanging basket.

Most varieties of lobelia have a somewhat trailing growth habit, although there are other varieties that clump. There are several different flower colors available, including a true sky blue. Other colors include purple, white, pink, and lilac. Most varieties have a tiny white "eye" in the center of each flower. While most varieties have green foliage, a few have a slight bronze tinge to the leaves.

Lobelia's small-but-numerous blooms appear through the summer and into the fall in most climates and attract pollinators, including butterflies, bees, and hummingbirds.

You can grow lobelia from seed or from small plants purchased at the nursery. Either way, it's usually planted outdoors in the spring and will begin to flower by early summer.

Be aware that while various species of lobelia have been traditionally used in herbal medicine, all parts of the plant may be toxic to pets and humans when consumed in large quantities.

Common Name Lobelia, annual lobelia, edging lobelia
Botanical Name Lobelia erinus
Family Campanulaceae
Plant Type Annual
Mature Size 6-9 in. tall, 9-10 in. wide
Sun Exposure Full, partial
Soil Type Moist but well-drained
Soil pH Acidic, neutral
Bloom Time Summer, fall
Flower Color Blue, pink, purple, white, red
Hardiness Zones 10 to 11 (USDA)
Native Area Africa
Toxicity Toxic to people, toxic to pets

Lobelia Care

Although Lobelia erinus is technically a tender perennial that may survive the winter in USDA zone 10-11, it is most often grown as an annual that is discarded at the end of its bloom time. Despite its compact, delicate appearance, lobelia does not require a lot of maintenance. It doesn't need to be deadheaded because the plant self-cleans its spent, small flowers. Nor do deer tend to eat it. Lobelia does, however, tend to decline if subjected to full sun during very hot summers. If this happens to your plant, you can revive it by cutting it back and then providing water on a regular basis.

Lobelia plant in rows full of deep purple flowers in sunlight

The Spruce / Evgeniya Vlasova

lobelia in a landscape

The Spruce / Evgeniya Vlasova

lobelia in the fall

The Spruce / Evgeniya Vlasova

Light

For the most part, lobelia isn't too picky about sunlight and can thrive in partial shade to full sun locations. However, if your summers tend to be very hot, it is best to plant lobelia where it will receive direct sun only in the morning and part-shade to shade in the afternoon. In areas with milder summers, grow it in full sun (as long as you water it regularly) to enjoy maximum flowering.

Soil

Lobelia likes rich, well-drained soil. Don't let conditions get soggy, however, which can cause root rot. If planting lobelia in a container or hanging basket, a good potting soil will keep this pretty plant blooming all season long.

Water

Keep the soil evenly moist, but not soggy. In areas with regular rainfall, you might not need to provide extra water. In drier areas, however, be prepared to water your lobelia every few days through the summer, and more often if the weather is exceptionally hot.

Temperature and Humidity

Annual lobelia does best in moderate temperatures and with moderate humidity. However, it can thrive even outside those conditions as long as you provide a little extra care. In hot climates, planting lobelia where it will be protected from peak afternoon sun can help prevent scorch or plant death. Regular watering will help maintain enough humidity for the plant to do well, but in very dry conditions, the leaves might shrivel. If you take quick action with the hose or watering can, often the plant will revive. Annual lobelia will not survive freezing temperatures, and is generally discarded in the winter.

Fertilizer

Since lobelia is a prolific bloomer and heavy feeder, you'll get the best results by fertilizing it every two weeks with a liquid fertilizer formulated for flowering plants. These typically are somewhat higher in phosphorus than in nitrogen and potassium, as phosphorus promotes more flowers.

Mix the fertilizer with water in a watering can according to package directions, and apply to the base of the plant, avoiding its leaves. Continue to fertilize your lobelia regularly through the summer to keep it flowering.

Types of Lobelia

Many plants go by the common name of "lobelia." Some are hardy perennials, others are cultivars of the tender perennial Lobelia erinus, which is usually grown as an annual. There is a wide range of color choices available, depending on which type you choose to grow. Here are some examples:

  • Cardinal flower (Lobelia cardinalis): Hardy perennial with red flowers and an upright growth habit; attractive to hummingbirds; reseeds easily
  • Great lobelia (Lobelia siphilitica): Hardy perennial with blue flowers and an upright habit
  • Lobelia erinus 'Laguna': Tender perennial with blue flowers and a trailing habit; developed by plant breeders to stand up better to hot summers than other trailing lobelias
  • Lobelia erinus 'Alba': Tender perennial with white flowers and a trailing habit
  • Lobelia erinus 'Lilac Fountain': Tender perennial with lilac-pink flowers and a trailing habit
  • Lobelia erinus 'Rosamund': Tender perennial with cherry-red flowers and a trailing habit

How to Grow Lobelia From Seed

Like most annual flowers, it's easy and economical to grow lobelia from seed. You'll also often have a better choice of varieties when planting from seed, rather than from nursery plants.

In cold-winter climates, it's recommended to start lobelia seeds indoors 6 to 8 weeks before the average last frost date for your area. Scatter the very tiny seeds evenly atop a seedling tray filled with seed-starting soil. Do not bury the seeds, however. Set the uncovered tray near a window that provides good light, and mist the tray with water to moisten the soil.

Continue to mist the soil daily, or as often as required to keep it moist, not soggy. The seeds should begin to germinate two to three weeks after sowing. Continue to mist the seedlings often enough to keep them moist but not soggy. If your tray is too crowded, carefully remove seedlings to

Once nighttime temperatures are regularly over 50 degrees Fahrenheit, it's time to plant your lobelia in the garden. Gently separate the seedlings, taking care not to tear their roots, and plant them in your desired location outdoors, whether in the ground or in a container.

In mild-winter areas, you can sow the seeds outdoors in the early spring, as long as nighttime temperatures are reliably more than 50 degrees Fahrenheit.

Space your annual lobelia plants 4 to 6 inches apart in containers and slightly further apart if planting directly into the ground.

How to Get Lobelia to Bloom

As long as you plant your lobelia where it won't be exposed to intense sun and heat, or in a full-shade location, this small, delicate-appearing plant generally bursts into bloom by early summer—in warm climates, it's often blooming by mid-May—with little need for pampering. Make sure to keep your lobelia moist; remember to fertilize it every couple of weeks, and your reward will be bountiful, small blooms in purple, blue, pink, or white, depending on the variety. There's no need to deadhead the spent flowers; annual lobelia drops them on its own.

When the weather gets very hot, Lobelia erinus does sometimes take a break from flowering. You can encourage another flush of flowers by gently shearing the plant back by around half and then watering well. Within a week or two, the plant will once again be covered with its small, white-eyed blossoms.

As fall temperatures begin to drop, your lobelia will start flowering less, but may still produce blooms until temperatures are regularly below 50 degrees Fahrenheit at night. At this point, you can pull the plants and discard them, or add them to your compost pile.

FAQ
  • Does lobelia come back each year?

    Perennial varieties of lobelia do come back each year. However, the common garden variety, Lobelia erinus, is most often grown as an annual and will not survive the winters in climates outside USDA gardening zones 10-11. It is possible for the plants to drop seeds, however, which may sprout and grow the following spring.

  • Does lobelia attract butterflies?

    Although each individual lobelia blossom is very small, the plant produces flowers in great quantities, and pollinators, including butterflies and hummingbirds, can't resist these pretty blooms.

  • Is lobelia fragrant?

    Although it produces beautiful flowers, unfortunately, the blooms of Lobelia erinus do not have much fragrance.

  • Is lobelia a good cut flower?

    While perennial varieties of lobelia can be beautiful cut flowers, the annual lobelia is best enjoyed in the garden. The thin stems and small flowers do not last well once cut from the plant.

Article Sources
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  1. Lobelia erinus. North Carolina State University.