Pedicularis canadensis

Canadian lousewort (Pedicularis canadensis, wood betony) is a relatively common species in remnant prairies, but it is very rare in cultivation, and it’s often rare in prairie restorations. Although seldom available at native plant nurseries, Canadian lousewort makes a wonderful garden plant: it provides excellent early-season interest, with purple ferny foliage when it first emerges and fun yellow pinwheel flowers a few weeks later; it’s very small and non-aggressive; and it’s also a bumblebee magnet, with one study in Iowa finding that Canadian lousewort is primarily pollinated by bumblebee queens, and in fact its flowers may be specially adapted to queenly pollination.¹

In my experience, the common name “Canadian lousewort” is not very common, but I’ll use it here because “wood betony” often refers to an unrelated European plant that is also common in herbal medicine: Betonica officinalis. The scientific name Pedicularis canadensis refers to its lousy-ness (“pedicular” refers to things related to lice) and its Canadian-ness, so “Canadian lousewort” feels appropriate.

Two factors in particular make this plant a little bit more challenging to successfully grow:

• Its seeds appear to not retain viability for long when stored dry at room temperature. I’ve discussed this trait previously in my post on growing bottle gentian (Gentiana andrewsii) from seed, so check out that article if you want to learn more about desiccation-sensitivity. Canadian lousewort seeds appear to rapidly lose viability when stored dry at room temperature.² So if you’ve bought Canadian lousewort seeds, stratified them, and watched them mold, the problem was probably the seed, not you.
• As a hemiparasite, it probably requires a host plant to thrive. I’ve discussed hemiparasitism before in my post on scarlet painted-cup (Castilleja coccinea). Canadian lousewort is likely an obligate hemiparasite, meaning that—despite having the ability to photosynthesize—it requires a host plant to complete its life cycle.³ I’ve seen a lot of people say that it prefers graminoids (grasses, sedges, rushes) as hosts, but I have not experienced that. We’ll leave that topic for a future blog, though. Note that it does not require a host plant to germinate.

So to successfully grow Canadian lousewort, three conditions must be met:

1. The seed must be fresh. Satisfying this condition is simple: to grow Canadian lousewort from seed, you’ll either need to find someone who will sell you fresh seed, or collect the seeds yourself (please follow all local regulations concerning gathering plant material). How fresh is fresh enough? I don’t know. With four-month-old seeds, I got 0% germination. This Grassland Restoration Network post says they got good germination for seed stored one month. So viability seems to remain high for the first month, but drops off somewhere before month four. This coming year I’ll test how viability changes over time, so stay tuned!
2. The seed must be subjected to an appropriate stratification regime. What is the appropriate stratification regime for Canadian lousewort? Read the rest of this article to learn about my results this past year.
3. The seedlings must be grown out with a suitable host species. What is the ideal host plant for Canadian lousewort? I’m not sure, but I’m currently growing my Pedicularis canadensis seedlings with these eleven prairie plants: Artemisia campestris, Bouteloua gracilis, Dalea purpurea, Geum triflorum, Ionactis linariifolia, Liatris cylindracea, Schizachyrium scoparium, Solidago ptarmicoides, Sporobolus heterolepis, Symphyotrichum oolentangiense, and Viola pedata. In a few months I’ll take measurements and post the results. According to Piehl (1963), Canadian lousewort is not very picky about what plants it parasitizes,⁴ but in my experience growing Orobanchaceae in a greenhouse setting, choice of host plant can make a difference, even when the hemiparasite is a generalist.

Two stratification regimes for germinating Canadian lousewort

Assuming that you have procured fresh-enough Canadian lousewort seeds, the next step in growing them will be to subject them to stratification. I heard from Alex Blondeau at Windflower Natives that Canadian lousewort responded well to both cold-moist stratification (~six months in the fridge) and to warm-moist followed by cold–moist stratification (~three months at simulated summer temperatures followed by three months in the fridge).

So I decided to test both of these methods on fresh seeds from the same lot to see if one method would have better germination.⁵ All seed was collected June 21, 2025 (this was late in the season, more on that later). Ten days after collecting my seeds, I began pretreatment:

• 219 seeds received six months cold–moist stratification. The seeds were mixed with damp play sand and stored in the fridge for six months.
• 219 seeds received three months warm–moist stratification followed by three months cold–moist stratification. Seeds were mixed with damp play sand, then subjected to simulated summer temperatures (in the dark) for three months (30°C days, 15°C nights). Then they were moved to my refrigerator for three months.

Both groups were treated for a total of six months. After their treatment period, I sowed them on ProMix BX, misted them with water to wash away the sand and settle the seed, and dusted them with fine vermiculite. They were left at simulated spring temperatures (20°C days, 10°C nights) with 14 hours of light and 10 hours of darkness per day.

At sowing time, many of the cold-only seeds had germinated in the fridge, but none of the warm-then-cold seeds had germinated. After sowing, the cold-only seeds began emerging after only a few days, but the warm-then-cold seeds took two and a half weeks to start emerging. I evaluated germination at two points in time: first, at three weeks after sowing; second, at five weeks after sowing. I only calculated statistical significance for the percentages at five weeks. Below are the results:

Ultimately, there was not even a whiff of statistically significant difference between the two treatments when measuring germination five weeks after sowing. However, the cold-only group was quicker to germinate, with germination complete at week three, whereas the warm-then-cold group was just starting to germinate at week three (but note that timing differences were not analyzed statistically). Both groups only achieved about 10% germination, which is much lower than I usually target. I can’t say with certainty why that happened, but here are my thoughts:

• I collected my seeds late—about 2 weeks later than usual. Most of the seeds had already fallen out of their capsules, so I was collecting the small fraction of seeds that remained. It’s possible these stragglers were either less viable or more deeply dormant than the general population of seeds.
• Given that many of the cold-only seeds had germinated in the fridge, I believe six months is too long a period for cold–moist stratification. By the time I sowed seeds, some of the germinants may have already died from spending too much time in the fridge.
• Conversely, given that it took the warm-then-cold group two and a half weeks to start germinating, dormancy was not totally broken at the time of sowing. So they likely needed longer stratification (my intuition is they needed more time in the fridge).
• I essentially surface-sowed the seeds. It’s possible that light inhibits germination (see my article on passionflower for more info on negative photoblasticity).
• I only tested germination at simulated spring temperatures. It’s possible they prefer simulated summer temperatures to germinate.
• I only stratified them at simulated summer temperatures. It’s possible they need stratification at simulated summer temperatures, then simulated fall temperatures, or else just simulated fall temperatures.
• I stratified seeds ten days after collection. It’s possible they require some period of warm-dry after-ripening (e.g., one month).

Rest assured I will test each and every one of these possibilities in the coming year! But if you’ve got a few hundred seeds, and only need a few dozen plants, either of these protocols could work for you.

But isn’t it odd that Canadian lousewort seeds would respond to both cold and warm-then-cold stratification?

It might seem odd to you that a species would respond to both cold and warm-then-cold stratification. But it doesn’t seem very odd to me, and there are at least two possible explanations for this phenomenon:

• Hypothesis 1: Canadian lousewort seeds have intermediate physiological dormancy. Canadian lousewort seeds are described by Baskin and Baskin (2014) as being physiologically dormant,⁶ which means that they have a physiological inhibition mechanism in the embryo; this inhibition often manifests as insufficient embryo push power to overcome covering-layer restraint.⁷ Baskin and Baskin describe three levels of physiological dormancy: non-deep, intermediate, and deep. Many seeds with intermediate physiological dormancy have the interesting trait that their relatively long cold stratification requirements can be reduced by a period of warm-moist stratification. One explanation for this trait is that it allows species adapted to long winters to extend their range to areas with relatively short winters. The precise level of dormancy that Canadian lousewort seeds have has not yet been described in the academic literature, but it’s possible that Canadian lousewort has intermediate physiological dormancy.
• Hypothesis 2: the warm–moist stratification isn’t breaking seed dormancy—it’s simply keeping the seeds moist until cold stratification begins. Put another way, the group receiving warm-then-cold stratification was essentially held in moist storage for three months, then cold–moist stratified for three months. This could explain why the warm-then-cold group was so much slower to germinate: the seeds received less time experiencing conditions necessary for breaking dormancy (near-freezing).

If all goes according to plan, in about one year I’ll have experimental results indicating which—if either—of those hypotheses is correct. ■

Have a question? If you have questions about Midwestern native plant propagation that you want answered in a future post, I’d love to hear from you! Shoot me an email at plantpropagationproject@gmail.com or leave a comment below!

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Notes

1. Lazarus Walter Macior, “Pollination Adaptation in Pedicularis canadensis,” American Journal of Botany 55, no. 9 (1968): 1031–35, https://doi.org/10.2307/2440468. ↩︎
2. I don’t (yet) have high quality evidence for this claim. Right now my evidence is only my own personal experience. When I have collected P. canadensis seeds, stored them dry for a few months, and then began stratification, I got no germination. But when I started stratification soon after harvest, I did get germination. ↩︎
3. As far as I know, there is no definitive proof that Pedicularis canadensis is an obligate hemiparasite. A few academic articles—citing Piehl (1963) and Kuijt (1969)—have casually claimed that Pedicularis canadensis is an obligate hemiparasite, but neither Piehl nor Kuijt (nor the later authors invoking them) actually demonstrate obligacy in the strict sense (i.e., failure to complete the life cycle without a host, ideally via a host-free control). For now, I consider it likely, but unsubstantiated, that P. canadensis is an obligate hemiparasite. Martin A Piehl, “Mode of Attachment, Haustorium Structure, and Hosts of Pedicularis Canadensis,” American Journal of Botany 50, no. 10 (1963): 978–85, https://doi.org/10.2307/2439904; Job Kuijt, The Biology of Parasitic Flowering Plants, Berkeley: University of California Press, 1969, https://doi.org/10.1525/9780520417793. ↩︎
4. Martin A Piehl, “Mode of Attachment, Haustorium Structure, and Hosts of Pedicularis Canadensis,” American Journal of Botany 50, no. 10 (1963): 978–85, https://doi.org/10.2307/2439904. ↩︎
5. Technically I didn’t test germination—I tested seedling establishment success, which I define as emergence above the soil surface and survival to week five. Germination refers simply to the point at which the radicle protrudes from the seed. It is possible—and common—for a seed to germinate, but fail to survive. For instance, when I tested gibberellic acid treatments on old bottle gentian (Gentiana andrewsii), many seeds germinated sensu stricto, but none of them survived. So reporting germination doesn’t necessarily help folks growing native plants for fun and for profit. Therefore I report the number of seedlings that germinate, emerge, and survive to week five. ↩︎
6. Carol C. Baskin and Jerry M. Baskin, Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination, Second Edition (Academic Press, 2014), 775. ↩︎
7. Same as above, page 41. ↩︎