Lobelia Flowers: Planting, Growing and Caring for 15 Types of Lobelia Herbs

Growing a Lobelia From a Seed, Cutting, or Seedling

Below are the things to consider when growing a Lobelia:

Growing From a Seed

Growing Lobelia from a seed is the best way to propagate the plant. This option will also give you the most variety from which to choose compared to buying a plant from a nursery.

If you live in a colder climate, prepare the seeds indoors about six to eight weeks before the last frost is expected in your region. If you live in a warmer area with milder winters, you can plant the seeds directly outdoors in early spring so long as evening temperatures don’t typically drop below 50 degrees.

One of the more important Lobelia facts to know is that, unlike some plants, Lobelia seeds do not require any sort of pre-treatment like soaking or cold stratification to encourage germination.

If growing indoors first, here are the steps to do so:

1. Put the seeds on top of the seed-starting soil in the tray but do not bury them in it.
2. Place the tray–uncovered–near a window that gets lots of light
3. Mist the soil so that it is evenly moist
4. Keep misting the soil as often as needed to keep it consistently and evenly moist
5. Seeds should start sprouting in about two to three weeks
6. Once temperatures are at least 50 degrees nightly, the seedlings are ready to be planted outdoors, provided they are large enough to handle and have grown real leaves
7. If planting in containers, place seedlings about four to six inches apart. If planting in the ground, plant at least six inches depending on the variety.

Growing From a Cutting

When growing Lobelia from a cutting, it must be taken from new growth. Choose a stem that is at least four to five inches long and has at least three or four nodes–the part of the plant from which the leaves grow.

Put the cuttings in moist potting soil, leaving half the stem above the dirt. Place the container in a shady spot.

The cuttings need to be kept very moist so mist them twice a day. The plant is ready to be planted in a new container or outdoors when you see a healthy amount of leaves and you can tug on it gently and it resists.

This means it has established new roots.

When To Plant Lobelia Plant

As for when to plant Lobelia for the best yield, it will generally be in the spring–be certain the last frost has passed.¹ Start germinating the seeds in February or March and transplant them outside about seven or eight weeks later.

If you live somewhere with really hot summers, it is good to plant them from late September through December. In these climates, the plants will thrive better in a shadier location.

Lobelia Growing Zone

The Lobelia growing zone is technically 9 to 11, but the actual growing zones for Lobelia (where to grow) are 3 to 11 for the most part.² Most species of Lobelia are perennials–flowers that grow back each spring and may live for at least several growing seasons.

But they can only thrive as perennials in the warmer growing zones of 9 to 11. Most people, however, grow them as annual flower and simply replant them every year. And if growing them this way, you can plant them in colder climates as low as zone 3.

Lobelia Growth Rate

The Lobelia growth rate can vary among species, but this is the general time frame for the most part. When it comes to how long it takes to grow Lobelia, if you germinate the seeds yourself, that will take about two to three weeks, and once the seeds go in the ground, the plant will grow to full maturity in about three to four months.

Best Growing Conditions for Lobelia

The best growing conditions for Lobelia are generally similar among species, but it is best to educate yourself about the specific variety you plan to grow to see if its needs differ in any way.

Here are a few of the most important planting tips for Lobelia:

Spacing

Some varieties grow more upright while others are more bush-like and spread very widely, so

how far apart to plant Lobelia will depend on which type is being planted. The recommended spacing is usually anywhere anywhere from six to 18 inches apart.

Sunlight

How much sunlight does Lobelia need each day? Generally, the plant does well with sufficient amounts of sunshine but can thrive very well in partial shade.

Ideally, it will be located somewhere it receives four to six hours of direct sun. In areas with milder summers, it will produce the most flowers when grown in full sun, provided it is watered regularly.

In areas with very hot summers, it is best to plant Lobelia in a location that only receives direct sun in the mornings and partial or complete shade in the afternoon.

Water

The watering needs for Lobelia plants will vary depending on your climate. It needs soil that is uniformly moist but not super-soggy and waterlogged.

If you live in a location with pretty consistent rainfall, it may not need any watering beyond this. If you live in a more arid climate, or there is a particularly hot stretch of weather in your region, it will need watering every few days.

Lobelia planted in containers, may need daily watering in these cases. Some species of Lobelia are more heat-tolerant than others, and if you live in a hotter area, it would be a good idea to consider these varieties.

Soil

Lobelia generally grows best in rich, slightly acidic soils, with a pH of 6.0 to 7.0. Adding a layer of compost will provide the plant with additional nutrients, retain moisture, and prevent the growth of weeds.

If growing in a container, it will thrive best with an all-purpose potting mix of higher quality.

Fertilizer

What makes Lobelia plants so popular is the abundant amount of colorful flowers they produce. But to grow all these beautiful blooms, they need a steady diet of rich nutrients.

(Image: Ольга (ZOlgaru)¹⁹)

Lobelias fall into the category of plants known as ‘heavy feeders’ meaning they need to be fertilized regularly.³ When first planted, use a time-release granular fertilizer, and then follow up with a liquid fertilizer every couple of weeks.

Use one specifically made for flowering plants, which contains higher amounts of phosphorus, a mineral known to encourage more flower growth. When applying liquid fertilizer, avoid the leaves.

Pruning and Maintenance

Generally, Lobelia plants do not require a lot of maintenance. Some varieties will automatically drop their dead flowers while others may require you to remove them, a process known as ‘deadheading.’

If your plant seems to be faltering, cutting the stems back by a third, combined with some watering and fertilizing over the next couple of weeks should help them bounce back–just be sure they get some shade in the afternoon.

15 Types of Lobelia

There are actually over 400 species of Lobelia, but below you will find descriptions of 15 of the most common types likely to be found in a home garden.⁴

They also look very beautiful when used for the front of borders or bed edging. They blossom in the spring, summer, and fall.

Foliage is usually darker green and the leaves have serrated edges. It blooms from June to October.

This is a particularly hardy variety of Lobelia and also does well in hotter temperatures. It is also one of the taller species

7. Laguna White

This variety of white Lobelia blooms in the spring, summer and fall. It is a trailing flower that looks great in hanging baskets and pots.

It can grow up to 12 inches high and spread twice as long. It is one of the more heat-tolerant types of Lobelia.

8. Monet Moment

This variety of Lobelia is a  tall upright plant, reaching heights of up to 31 inches. It produces brilliant magenta-pink flowers in large clumps that bloom in the summer and fall.

9. Hadspen Purple

This variety has rich dark green or purple leaves with deep shades of purple or violet flowers. It is an upright plant that can reach heights of two feet and blooms in the summer and fall.

10. Lobelia cardinalis “Black Truffle” (Black Lobelia)

Black Lobelia initially sprouts black leaves that transform into a rich shade of chocolate brown. Like its parent species, the red Lobelia, it has beautiful deep red flowers. It blooms in the summer and fall.

Companion Plants For Growing Lobelia

Between coming in a variety of colors and not having any particularly demanding or special growing conditions, you will have a large variety from which to choose when it comes to companion plants for growing Lobelia.

Shrubs

Pairing Lobelia with shrubs is mutually beneficial. They provide nice ground cover great for suppressing weeds, and the shrubs will give Lobelia plants the shade they need to thrive in certain areas with lots of summer sun.

Good choices include azalea, hydrangea, daphne, and rhododendrons. If growing this plant with shrubs, it may need some extra watering to keep the roots moist.

Perennials

Lobelia varieties that tend to bloom earlier in the spring go well with perennials that bloom earlier in the season as well. Some plants that grow in similar conditions and pair well with Lobelia include ferns, columbine, lily of the valley, brunnera, astilbe, hardy fuchsia, and hardy geraniums.

Annuals

Choose annuals that bloom in the early spring to midsummer. Good choices include calibrachoa, pansies, alyssum, coleus and ageratum.

Lobelia typically has a smaller root system than most annual plants making it a good choice to fill in empty spots in your outdoor space.

Good Plants for Container Lobelia

For Lobelia grown in containers, good companion plants include sweet alyssum, violas pansies, calibrachoa and geraniums.

Plants To Avoid

Plants that do not need a lot of watering and thrive best in the hot sun are not a good match for Lobelia, which needs pretty moist soil and protection from really hot weather. Examples include juniper, ornamental grasses, yarrow, seedflower, and coneflower.

Other plants to avoid with the delicate Lobelia are those that spread fast or have a tendency to take over the space and crowd out other plants

How To Stop Lobelia Disease

When it comes to how to stop Lobelia disease, know that the plant isn’t highly vulnerable to disease.⁶ It may look delicate but is fairly hardy in that regard. Lobelia disease prevention will mainly consist of proper plant maintenance.

Spider Mites

Spider mites are one of the most common pests of the Lobelia plant. They suck the sap out of the plant, causing the leaves to wilt, rot or become discolored.

Signs include the underside of the leaves feeling a bit dry or sandpaper-like. When it comes to organic means of dealing with spider mites and other pests that may disturb this plant,  one of the most recommended forms of natural pest control for Lobelia is neem oil.

Other Insects

Other potentially problematic insects include the negro bug, the red-banded leafroller, and wireworms.

Fungal Diseases

Basal or root rot is one of the more common fungal diseases. Treatment primarily involves removing infected plants since fungicides are not particularly effective.

Gray mold will grow on old flower petals so removing dead flowers before it has a chance to develop is the best way to prevent it. If it has spread to other parts of the plant, fungicides may help.

Irregularly shaped, brown leaf spots may result from several different fungi and bacteria as well. Sulfur is one potential treatment.

Rust disease causes rust-colored growths on the leaves, and causes yellowing and discoloration on the surrounding tissue. It typically interferes with the plant’s growth as well. Treatments include sulfur and mancozeb.

Smut disease occurs when fungi attack the reproductive organs of the plant, and grow black masses of fungal spores in their place. It also causes light spots on the leaves. Removing infected plant matter is typically the only treatment required for this disease.

Stem rot first manifests as yellowing of the lower leaves of the plant,  which will start to wilt and eventually die. Other signs include a white cotton-like mass of fungus on the soil or around the crown of the plant.

Treatment includes removing surrounding topsoil and infected plant matter.

How To Identify Lobelia

Different species of Lobelia may have different characteristics, but the following describes the general appearance of this genus of flowers:

Lobelia Leaves

Lobelia leaves are generally green to dark green though some varieties can have bronze or brown foliage. They are wide at the base and become narrower, tapering to a fine point at the very tip.

(Seed Image: Dwight Sipler²⁰, Leaf Image: Rob Hille²¹, Lobelia Plant Image: Neelix²²)

The leaves follow an alternate pattern, meaning they grow a single one at each node and do not have one directly opposite them

Lobelia Flower

The Lobelia flower tends to have about five petals, with the top two standing upright and the bottom three making a fan-like shape. They come in a wide range of colors, with the best known varieties having various shades of blue with white eyes in the center.

Other colors include pink, red, violet, and white. Lobelia flowers will either have bushy or trailing habits.

The bushy variety can spread quite wide, sometimes twice its length. Varieties with trailing habits make great container plants–they look very pretty spilling over the sides.

Between the large variety available and the fact they can be grown as an annual plant in a wide range of climates, this plant is a great choice for your garden.

Delicate Lobelia flowers give them a fragile appearance that suggests they require careful care but they are pretty low-maintenance, which just adds to their appeal.

Frequently Asked Questions About Lobelia