From a purely visual standpoint, Lobelia seeks companions that complement its growth habit and color palette. Lobelia, particularly the trailing varieties like 'Regatta' or 'Cascade', forms a mound or spills gracefully over the edges of containers. Its flowers are most commonly found in vibrant shades of blue, violet, white, and magenta. To create a harmonious display, plants with contrasting forms are ideal. Upright growers like Salvia (such as the dwarf 'Victoria Blue' variety) or Veronica provide a vertical accent that plays beautifully against Lobelia's spreading nature. For color harmony, white-flowered companions like Sweet Alyssum or Bacopa create a cool, classic combination with blue Lobelia. For a bolder, warmer contrast, the soft, muted tones of Diascia or the bright yellow blooms of Lysimachia (Creeping Jenny) offer a stunning visual counterpoint that makes both plants stand out.
A successful container partnership depends on shared environmental needs. Lobelia is a plant that thrives in consistently moist, well-draining soil and prefers full sun to partial shade. It is crucial to select companion plants with similar requirements to prevent stress. Many classic container plants are excellent matches. For instance, Impatiens and Begonias both enjoy moist soil and partial shade, making them perfect partners for Lobelia in less sunny locations. In full sun containers, Petunias and Calibrachoa (Million Bells) are ideal companions. They share Lobelia's appetite for moisture and sun, and their prolific blooming habits create a long-lasting, floriferous display. Avoiding drought-tolerant plants like most succulents or Lavender is essential, as their need for dry soil between waterings would quickly lead to root rot for the moisture-loving Lobelia.
Beyond aesthetics and culture, some companion plants can offer functional benefits. While the scientific evidence for companion planting is often anecdotal, especially in the confined space of a container, certain principles can be applied. Lobelia can be susceptible to pests like aphids. Interspersing plants known for their pest-repelling properties, such as Ageratum or Marigolds, may help create a less inviting environment for these insects. The strong scent of Marigolds, in particular, is believed to deter a range of pests. Furthermore, planting a "spiller" like Lobelia with a "thriller" (tall, focal point plant) and a "filler" (mounding plant) is a classic container recipe for a reason. The dense foliage of fillers, such as Coleus or Heuchera, can help shade the soil surface, reducing moisture evaporation and keeping Lobelia's roots cooler and happier during hot weather.
Just as important as choosing the right companions is knowing which plants to avoid. Lobelia's primary demand is for consistent moisture. Therefore, it should not be paired with plants that prefer dry, arid conditions. Mediterranean herbs like Rosemary, Thyme, and Lavender will suffer in the damp soil that Lobelia requires. Similarly, aggressive growers should be avoided in a container's limited real estate. While not typically a problem in pots, fast-spreading groundcovers could potentially outcompete the more delicate Lobelia for water and nutrients. It is also wise to consider light requirements; a sun-loving Lobelia will become leggy and fail to bloom if placed with a companion that requires deep shade, forcing the entire container into a low-light situation.
