How To Grow and Care For Lobelia

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. Lobelia spreads, but not aggressively.

Most varieties of lobelia have a somewhat trailing growth habit, although other varieties clump. There are several different flower colors available, but it's well known for its unique true sky blue hue. 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. Plant it outdoors in the spring and it will begin to flower by early summer. All parts of the plant are toxic to pets and humans.

Lobelia Care

Although Lobelia erinus is technically a tender perennial that may survive the winter in USDA zones 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. Though lobelia is typically a plant that prefers more sun than shade, it 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 regularly.

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.

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 the 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 it 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 will have more success with seeds than propagating lobelia in other ways. 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. 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. Take these steps:

1. Scatter the very tiny seeds evenly atop a seedling tray filled with seed-starting soil. Do not bury the seeds, however.
2. Set the uncovered tray near a window that provides good light.
3. Mist the tray with water to moisten the soil.
4. 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.
5. Once nighttime temperatures are regularly over 50 degrees Fahrenheit, it's time to plant your lobelia in the garden. First, harden off the plants gradually to allow them to adjust to outdoor conditions. Then, gently separate the seedlings, taking care not to tear their roots, and plant them in your desired location outdoors, whether in the ground or a container.
6. Space your annual lobelia plants 4 to 6 inches apart in containers and slightly further apart if planting directly into the ground.

Potting and Repotting Lobelia

Lobelia is typically used to edge the front of a flower border, but it is also heavily used in a container garden or can be seen spilling over the sides of a hanging basket. Lobelia prefers moisture, especially in hot weather, but it does not like to be soggy. Any container should have plenty of drainage holes. Consider plastic containers to retain moisture but if you choose ceramic pots, just remember to check when to water the plant since it will dry out faster. If planting lobelia in a container or hanging basket, a good potting soil will keep this plant blooming all season long.

Common Pests

The main pest that can damage lobelia is the spider mite. A minor spider mite infestation can be handled with gentle sprays of cold water. A severe infestation may require insecticidal soap, neem oil, or pesticides as a last resort. Corn earworms also like lobelia, and they eat holes in leaves which can make the plant vulnerable to developing fungal diseases. Manual removal and insecticides can help eliminate the corn earworms before too much damage is done.

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, but non-fragrant 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.

Common Problems With Lobelia

This delicate plant can have its share of problems thanks to interested pests and its light sensitivities. Here are a few signs to look for:

Browning Foliage

Overwatering is a common issue with lobelia. Since it doesn't like hot weather, you may tend to overwater and as a result, the leaves will brown. On the other hand, lobelia turns brown if it's overheated. Try moving the container to shade or add temporary shade if lobelia is planted in the ground but drying up under the sun.

Leaves Curling

Along with extreme heat, lobelia also can't handle very dry conditions. If the plant is feeling any sort of drought conditions, the leaves may brown and start to curl up around the edges to protect themselves. Do as you would with browning foliage and give the plant more shade and watering.

Spotted Leaves

Mites may be attacking the plant by sucking out the juices from its leaves, turning them spotty. As soon as you see some spots, use insecticidal soap to remedy the situation.

Brown Base

If the foliage isn't browning, but it appears as though the base of the mound is turning brown, you could have corn earworms, which is another type of insect infestation. This can be tough to treat if the damage is already done (holes in leaves). The damage can make the plant susceptible to fungi diseases so it's best to remove damaged sections immediately so the problem does not spread.