How to Grow and Care for Lobelia

"Annual" Lobelia a Plant of Many Uses

Closeup of flowers of Lobelia erinus.

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So-called "annual" lobelia is a widely grown plant that belongs to the Campanulaceae (or "bellflower") family. This makes it a relative of such landscape plants as:

This type of lobelia has a trailing growth habit and comes in many colors. It is commonly sold in the annuals section of the garden center and has a wide variety of uses even in regions where it is not a perennial.

Botanical Name Lobelia erinus
Common Name Annual lobelia, edging lobelia, lobelia
Plant Type Tender perennial
Mature Size 6 to 9 inches in height, with a slightly greater spread
Sun Exposure Full sun to partial shade
Soil Type Friable, evenly moist, and well-drained
Soil pH Slightly acidic to neutral
Bloom Time In the North, lobelia blooms all summer and into fall, until the first frost.
Flower Color Blue, lilac-pink, purple, white, cherry-red
Hardiness Zones 10 to 11
Native Area Southern Africa

Lobelia Care

This type of lobelia is perennial only in zones 10 and 11. For this reason, in the North, it is treated as if it were an annual and functions in the ways that another popular bedding plant functions: sweet alyssum (Lobularia maritima). But lobelia comes in more colors than sweet alyssum and is more versatile due to the fact that it performs better across a spectrum of sunlight conditions ranging from full sun to partial shade.

Lobelia does not require a lot of maintenance. It does not need to be deadheaded because the plant self-cleans. Nor do deer pests 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.

Light

One of the selling points of lobelia is that it is not fussy about sunlight levels, flowering nicely in anything from full sun to partial shade. In the South, it is best to grow it in partial shade. In the North, grow it in full sun (as long as you water it regularly) to enjoy maximum flowering.

Soil

Lobelia likes rich, well-drained soil.

Water

Keep the soil of lobelia evenly moist.

Fertilizer

You can fertilize lobelia with compost, but, since it is a heavy feeder, many gardeners prefer to feed it with a liquid fertilizer every two weeks.

Varieties of Lobelia

Many plants go by the common name of "lobelia." Some are hardy perennials, others are cultivars of the tender perennial. 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
  • 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

Uses for Lobelia in the Northern Landscape

Its trailing growth habit, dense flowering, and tolerance for either sun or shade make "annual" lobelia a highly versatile plant. Here are just a few of the many uses for it during the summertime in a Northern landscape:

  • As a flowering ground cover
  • In rock gardens
  • In the United States, use lobelia with blue flowers, along with red salvia (Salvia splendens) and white petunias (Petunia x hybrida), in patriotic landscaping displays (July 4th plantings and plantings around cemetery monuments on Memorial Day).
  • Use a lobelia with white flowers in a moon garden.
  • Grow your lobelia in a hanging basket and display it on a porch.
  • Install several lobelia plants along the edge of a mixed container garden, such as a whiskey barrel, and display it on your patio. The trailing growth habit of the lobelia allows it to cascade down the sides attractively.
  • Likewise, as an element in mixed window boxes, lobelia can be the plant that hangs down the side of the window box, while taller plants such as Victoria blue salvia (Salvia farinacea 'Victoria Blue') provide the backdrop.
  • Use lobelia as an edging plant along a walkway.
  • Plant lobelia in your butterfly garden as a short plant to complement taller species such as common milkweed (Asclepias syriaca).