Desmodium Canadense is one of the more underappreciated flowering perennials native to North America. Commonly known as Showy Tick Trefoil, in this article I will tell you all about this plant including it’s growing characteristics, seed germination requirements, and a detailed physical description with photos.
Showy Tick Trefoil is a herbaceous flowering perennial native to the upper Midwest, North Eastern United States, and into Canada. As it’s name implies, it makes beautiful pink-purple blooms in July/August. As a legume, it will fix nitrogen to the soil for use during the growing season. This makes Showy Tick Trefoil a great choice for poor soils, as it makes it’s own fertilizer.
Now lets take a look at the reference table with some key facts about Showy Tick Trefoil:
Showy Tick Trefoil Reference Table
|Scientific Name||Desmodium canadense|
|Common Names||Showy Tick Trefoil|
|Height||3-5′ (1-1.6 m)|
|Spacing||18″-24″ (45-60 cm)|
|Sunlight||Full sun, partial shade|
|Soil Type||Clay, loam|
|Soil Moisture||moist to dry|
|Bloom Time & Duration||Mid-summer lasting about 3 weeks|
|Bloom Color||pink to purple|
|Larval Host||Eastern Tailed Blue, Hoary Edge, Silver-spotted Skipper|
|Native Range||Upper Mid-West, North Eastern USA / Canada|
|Notes:||Excellent food source for game animals|
Full sun or partial shade is basically all that is needed to grow Showy Tick Trefoil. It is readily adaptable to many different soils from hard rocky clay (my garden) to loamy soil. Additionally, it has a taproot that makes it drought tolerant. Yet it also can thrive in moist soils along pond edges.
Showy Tick Trefoil will look its best in clusters rather than single specimens. I dense planting will yield a forest of pink-purple blooms and be quite attractive.
It is also a great species to plant in a micro-prairie or wildflower garden. Having it bloom as a companion to other mid-summer bloomers such as Heliopsis, Echinacea, or Rudbeckia makes for a stunning show.
Note that in disturbed areas with low competition, Showy Tick Trefoil can spread aggressively from self-seeding. I’ve thinned out many seedlings over the years to make room for other plants.
Showy Tick Trefoil can be found in prairies, roadsides, railroad areas that revert to prairie, open woods/thickets and along pond/stream edges. It seemingly can grow in any soil, dry to moist and sand to clay.
Showy Tick Trefoil is a pollen producing plant, and has no nectar. So, the flowers will only attract bees. Six different species of long-tongued bees frequent this flower (Robertson, 1929) . But, this flower is open pollinated, meaning the wind will pollinate the flower in absence of bees.
However, this doesn’t mean that butterflies don’t visit. Showy Tick Trefoil is a host plant to 3 different butterflies/skippers (Eastern Tailed Blue, Hoary Edge, Gray Hairstreak, Silver-spotted Skipper).
In addition to bees and butterflies, numerous other insects visit this plant including leaf miners, weevils (eat seeds), and gall flies. I have particularly noticed Japanese Beetles feeding on the foliage of my plants. Luckily, I have enough of them so that no single plant looks bad (perhaps another reason to not grow isolated specimens).
The foliage of Showy Tick Trefoil will be browsed by deer and rabbits. The seeds are eaten by numerous game birds and mice, including turkey, quail, grouse. The foliage also provides cover to birds/mammals.
Another point of interest, Showy Tick Trefoil is often utilized in prairie restoration.
Showy Tick Trefoil is susceptible to powdery mildew. The effects of which are cosmetic. Planting in an area with full sun and decent air flow can help reduce the incidence of powdery mildew.
In addition to powdery mildew there are several viruses  that can infect Showy Tick Trefoil, often with insects as the transmission vector. Although I should note that I have grown this plant for years, and never had any issues.
How to grow Showy Tick Trefoil from seed
Germinating Showy Tick Trefoil seeds is really quite easy. It doesn’t require cold stratification which allows you to start plants anytime after the last frost. But, my simple process is below:
- Scarify seeds by rubbing the seed on sand paper. Lightly rub  a seed on, or in between two sheets of sandpaper until the brown outer coating has been worn away and you can just begin to see the white interior
- Optional, soak seed in water overnight to reduce germination time
- Plant Seeds 1/4″ (6 mm) deep in pots filled with moist potting soil.
- Place pots in location that receives morning sun/afternoon shade. Keep soil moist until germination, which can take up to about 2-3 weeks.
- Transplant seedlings to final location. Space the seedlings 18-24″ apart.
You can also direct sow Showy Tick Trefoil. Just rough up the soil and plant seeds ~1/4″ deep in the fall. Thin seedlings to 18-24″.
You should be vigilant about protecting the young seedlings from deer and rabbits.
Showy Tick Trefoil Identification
The overall plant will reach a height of 4-5′ in good conditions with limited competition. Large specimens can reach 18-24″ diameter for spacing. If it reaches a tall height, it may be prone to getting knocked over by deer or high winds. If knocked over, it may lay on ground for the remainder of the season.
The stalk is erect and green in color, and small hairs. There will be some branching with flowers on larger plants.
I’ve always found Showy Tick Trefoil easy to identify by leaves early in the season, as well as seedlings. Leaves are compound, generally consisting of 3 on mature plants. Individual leafs are oblong/lanceolate in shape but are rounded at the tips. The leafs are generally 2-4″ (5-10 cm) long, by 1/2 as wide.
The leaves are rough to the touch, mainly due to the underside. The underside of the leaves have small hairs that grab on to clothing or fur of animals walking by.
Flowers are on top of the stems from both the main stalk and any branching. There will be clusters of small 1/2″ (12 mm) pink-purple flowers that change to blue with age. Flowers are typical ‘pea’ or legume flowers.
Flowering will last for approximately 3 weeks in mid-summer. After which pea pods will start to form. Each pod generally holds about 3-5 seeds. The pods are covered with hairs that, like the leaves, will stick to your cloths or the fur of animals. In this manner the mother plant can disperse its seed far and wide.
Showy Tick Trefoil has a taproot that is about 4-10″ long. The taproot is about 1/2″ diameter tapering as it goes deeper.
The root has a symbiosis with fungus within the soil, allowing the plant to fix nitrogen from the air into the soil/roots. Research has shown that the amount of biomass of Showy Tick Trefoil grown in a season will depend on the amount of symbiotic fungus present in the soil. 
 – Flowers And Insects. Lists of Visitors of Four Hundred and Fifty-Three Flowers. Charles Robertson, 1929.
 – Host Range and Some Properties of Desmodium Yellow Mottle Virus. H. J. Walters, H. A. Scott. 1971. University of Arkansas.
 – Germination and Seedling Growth of Desmanthus illinoensis and Desmodium canadense in Response to Mechanical Scarification. Michael W OLSZEWSKI; Courtney Young ; Joel Sheffield. HortScience. 2010, Vol 45, Num 10, pp 1554-1558, 5 p ; ref : 1/2 p
 – Fungi Fun: the Effects of Commercial Mycorrhizae on the Growth of Desmodium canadense and Salvia azurea. Brown, Fisher, Hamilton, Jorgensen. Oklahoma State University, Department of Plant Biology, Ecology, and Evolution
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