How to Plant & Grow Purple Lobelia In Ponds (Lobelia vedrariensis)

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Purple lobelia in bloom near a pond
Purple lobelia in bloom. Photo by Photo by David J. Stang [CC BY-SA]
Purple lobelia belongs to the family Campanulaceae, also known as the bellflower family due to the often bell-shaped flowers of its members. Lobelias have a very characteristic, recognizable flower shape that is two-lipped – two unfused petals are on the upper lip, and three more prominent fused petals are on the bottom lip.

With striking violet flowers, purple lobelia is attractive to bees, hummingbirds, butterflies, and moths and so can be planted about to attract and support pollinator populations.

Purple lobelia doesn’t really have a true native range, as it’s a man-made hybrid created by cross-breeding cardinal flower (Lobelia cardinalis) and blue lobelia (Lobelia siphilitica) to obtain vivid deep purple flowers. It’s largely utilized as a decorative garden plant, but has become naturalized in some portions of the U.S. and Europe.

Like other lobelias, purple lobelia is decent at filtering water when growing near water and as such can be utilized in wetland reconstruction projects, both to improve water quality and provide an attractive aesthetic.


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Purple Lobelia Fact Sheet:
Herbaceous Perennial
USDA 4-9
Full sun to partial shade
June – September (Summer to early Fall)
Height up to 120 cm (48 in), 1 to 2 in blooms
up to 5.08 cm (2 in) water depth, or damp soil
pH 4.5-7.5

Purple Lobelia Growth, Hardiness & Climate

a purple lobelia blooming in a garden pond
Photo by Magnus Manske [CC BY-SA]

A slower grower, purple lobelia takes approximately two years until it reaches maturity and is able to flower. Most mature lobelia vedrariensis are between 2.5 and 4 feet tall with a total spread of about a foot. During the second year of growth, purple lobelia will typically begin to bloom in June, depending on the region and climate, and continue blooming into September.

It’s hardy to USDA zones 4 through 9, and as an incredibly resilient plant can withstand frost as well as temperatures as high as 90° F. Full sun and partial shade both work well for purple lobelia – generally, as long as its roots are kept wet, it’ll likely be happy and healthy.

How to Plant Purple Lobelia In Ponds

several lobelia vedrariensis blooming in a pond with cattails and sedges
Photo by Magnus Manske [CC BY-SA]

Purple lobelia is quite hardy and, as a marginal plant, can be planted both directly in water and terrestrially, so long as soil is not allowed to dry out. Loamy soils are best, and can range from sandy loam to clay loam. This gorgeous plant can be planted in water or damp soil deep enough to cover one to two inches of the stem above the roots.

Seeds can be planted in half of an inch to an inch of damp soil, and if desired transplanted into water once the plant has matured. Both seeds and mature plants can be covered with two to three inches of mulch to hold in moisture and nutrients, as well as keeping the soil warmer.

How to Care For & Maintain Purple Lobelia

A tough plant, purple lobelia doesn’t require much so long as it has access to plenty of water. It can be trimmed as desired without harming the plant, and to prevent overgrowth. Clip off any dead or dying leaves and flowers to prevent them from falling into the pond, and clean any fallen foliage from the water to maintain water quality and prevent fish from eating it.

How to Winter Purple Lobelia In Ponds

Like most other lobelias, purple lobelia is a hardy evergreen perennial. Once winter hits, it’ll die down to its basal rosettes that will resprout the following spring. If planted in water, the lobelias will need to be transplanted into either soil above water or into pots and brought indoors for winter as freezing water could fatally damage the rosettes.

As a hybrid, purple lobelia can be somewhat difficult to obtain and so trying to keep it alive through winter is likely your best bet to keeping this plant around.

Is Purple Lobelia Toxic, Poisonous or Invasive?

Lobelias, including the purple lobelia hybrid, contain the compound lobeline. Lobeline behaves similarly in the body to nicotine, but to a lesser effect, and as such can be used to help curb nicotine addictions and withdrawal symptoms. However, if ingested in too large of an amount, lobeline becomes toxic and can cause nausea, vomiting, and diarrhea.

Due to being a fairly recently created hybrid, there are few publications on purple lobelia’s environmental impacts. However, it can be reasonably deduced from the available literature that it is not, as of right now, considered to be invasive anywhere in the world as it’s primarily used as a garden plant and doesn’t seem to overtake natural areas quickly

Is Purple Lobelia Plant Edible? Will Fish Eat it?

Due to the presence of toxic lobeline compounds, purple lobelia should not be eaten by fish. A small amount here and there is likely fine, but do keep fallen foliage and flowers cleaned out of the pond. You can also plant purple lobelia in aquatic pots if you have some fish that show interest in roots.

Where to Buy Purple Lobelia & Seeds? (UK & US)

Purple lobelia can be somewhat difficult to obtain due to being a man-made hybrid. It can most easily be found from online retailers, but some specialized nurseries may propagate it or it could be ordered in.

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2 thoughts on “How to Plant & Grow Purple Lobelia In Ponds (Lobelia vedrariensis)”

  1. Good article. Except I would edit this have proper use of botanical names the genus is always capitolized , the the specific epithet is small letters
    Lobelia cardinalis


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