Lilium philadelphicum

Lilium philadelphicum is very easy to germinate, but I’ve seen a lot of not-so-great germination protocols for this plant circulating on the internet. My protocol yields germination rates of about 90% and requires only nine weeks of cold stratification (and I bet you could get away with less time in the fridge).

Although I use a 20/10° C temperature regime when sowing the seeds (read more about temperature regimes here), L. philadelphicum also germinates well at room temperature (constant 20° C), which makes it a good choice for those who don’t want to use heat mats and thermostats. I’ve also tested it with a 15/6° C temperature regime, and I did get some germination, but it was much slower (see table below).

I don’t yet have a number for exactly how long they take to reach transplantable size. Conventional wisdom is that these should stay in the greenhouse for at least two years, but I’m assuming that’s in an unheated greenhouse (so two years is 10 to 12 months of active growing). I planted out some 10-week seedlings a few years ago, and they all died, so clearly that was a mistake. This year I will plant some out when they’re five months old, and I’m curious to see if those make it. I’ll update this page when I have a firm answer! ■

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

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Notes