Perennial Solutions: Lobelia Cardinalis ‘Black Truffle’ By Paul Pilon

There are numerous definitions of the word 'striking.' One definition is: conspicuously attractive or impressive. 'Striking' is precisely the word that comes to mind when I see Lobelia cardinalis 'Black Truffle'. The combination of its dark foliage coloration and bright cardinal red flowers are just stunning together.

'Black Truffle' forms attractive, bushy upright plants with dramatic, dark chocolate-purple foliage and bold red flowers. The new leaves emerge nearly black and fade to a deep, iridescent maroon as the plant matures during the heat of the summer. The bright cardinal red flowers appear in the mid summer and continue well into the fall.

Lobelia 'Black Truffle' was discovered by native plantsman Peter Heus of West Virginia and is brought to the market by Plants Nouveau. This eye catching lobelia is a true perennial with hardiness throughout USDA hardiness zones 3 to 8. It can be grown in average to moist soils and prefers full sun. 'Black Truffle' grows three to four feet tall by two to three feet wide. Hummingbirds are highly attracted to them; additionally, cardinal flowers also attract butterflies into the garden and are resistant to deer. This native perennial is perfect for use near water features and along creeks or ponds.

This cultivar is a true selection of the native species and is NOT a hybrid like the other dark leaved cultivars on the market. 'Black Truffle' is impressive and is eye-catching in both garden centers and in the landscape.


Lobelia 'Black Truffle' is vegetatively propagated by means of tissue culture and cuttings. Since a plant patent is being sought (PPAF – Plant Patent Applied For), unlicensed propagation of this cultivar without permission of the applicant is currently prohibited.


Growers commonly transplant one rooted liner into one-gallon or larger-sized containers. When transplanting, the plugs should be planted so the original soil line of the liner is even with the surface of the growing medium of the new container. Lobelia perform best when they are grown in a moist, well-drained medium. They require an average amount of irrigation; it is best to keep them uniformly moist and avoid keeping them overly dry or consistently wet. Lobelia can be grown using moderate fertility levels. Growers using water soluble fertilizers either apply 150 to 200 ppm of nitrogen as needed or feed with a constant liquid fertilization program using rates of 75- to 100-ppm nitrogen with every irrigation. Controlled-release fertilizers can be applied as a top-dress onto the media surface using the medium labeled rate or incorporated into the growing mix prior to planting at a rate equivalent to 0.9 to 1.1 pounds of elemental nitrogen per yard of growing medium. The pH should be maintained at 5.8 to 6.4.

'Black Truffle', like many perennial lobelias, is a naturally tall plant and may require various height management strategies during production. The first strategies entail providing adequate space between the plants and avoiding excessive nutrient and/or moisture levels during the growing phase. If additional height control is needed, several commercially available plant growth regulators effectively control elongation. I find spray applications of 2,500-ppm daminozide (B-Nine, Dazide), 5-ppm uniconazole (Concise, Sumagic) or a tank mixture of these growth regulators (2,000-daminozide plus 3-ppm uniconazole) to be highly effective at controlling the plant height of cardinal flowers. It is usually necessary to apply two or three applications at seven-day intervals to obtain the desired results.

Insects and Diseases

There are only a few problems with insects or diseases that growers are likely to experience when growing lobelia. Occasionally, aphids,
leafhoppers, slugs, snails, two-spotted spider mites and western flower thrips may be observed feeding on cardinal flower. Of these pests, aphids occur the most frequently. Insects and mites usually do not cause significant injury to the plants.

The plant pathogens growers may observe on occasion are Botrytis, crown and root rots (Pythium, Rhizoctonia, Sclerotinia and Sclerotium), leaf spots (Cercospora,
Colletotrichum, Phlyllosticta and Septoria), rust and smut (Entyloma). Although, this seems like a long list and lobelia appear susceptible to numerous diseases, they can generally be grown without the presence of plant pathogens. Of the diseases, Pythium occurs most frequently. With good watering management, adequate plant spacing and plenty of air circulation, most of these diseases can avoided.

Generally lobelia can be grown without implementing preventative control strategies. Growers can detect the presence of insects and diseases using routine scouting programs and determine if and when control strategies are necessary.

Temperatures and Scheduling

Lobelia 'Black Truffle' naturally flowers in mid summer. Due to the dark foliage coloration, it can easily be marketed as a foliage perennial when it is not in bloom. For early spring sales, it is best to plant liners into the final container during the early fall; allow them to become established and bulk up slightly, vernalize them, and then force them to bloom in the early spring using moderate to low production temperatures of 65¡ F. Summer flowering plants can be obtained by planting the liners in the spring.

To my knowledge, the specific requirements for flowering of 'Black Truffle' have not been researched. However, from my observations these requirements are likely similar to other cultivars on the market. Lobelia does not have an obligate cold requirement for flowering. They are not considered cold beneficial, since vernalization does not result in earlier flowering, but plants that have been vernalized grow more vigorously.

Lobelia which have received at least six weeks of cold will flower under any day length; it does take up to two weeks longer for them to bloom under short day lengths (<14 hours) than with day lengths greater than 14 hours. Conversely, plants that have not been vernalized must be grown under long day lengths (>14 hours) in order for them to consistently produce flowers. When the days are naturally short, long day lengths can be achieved by day extension or night interruption lighting, providing a minimum of 10 footcandles of light during these treatments.

For early season sales, I recommend growers use production temperatures of 65 to 70¡ F to force lobelia 'Black Truffle' into bloom. At these temperatures, it will flower in approximately nine to 11 weeks.


Lobelia 'Black Truffle' is brought to the market by Plants Nouveau ( North Creek Nurseries ( is currently the exclusive supplier of 'Black Truffle' liners.

Perennial Solutions: Lobelia Cardinalis 'Black Truffle'

Paul Pilon

Paul Pilon is a horticultural consultant, owner of Perennial Solutions Consulting (, and author of Perennial Solutions: A Grower's Guide to Perennial Production. He can be reached at 616.366.8588 or

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