Published by Brian Wagner on 11/20/25 in “Growing Flowers from Seed.”
Polemonium caeruleum L. (commonly called Jacob’s Ladder & referred to as ‘Greek Valerian’) is an herbaceous flowering perennial native to probably the entire European and Asian continent. It is very widespread but it favors cool, moist conditions in which to colonize. It is hardy to Zone 3 and will flower in spring where winters are mild, while for the rest of the temperate world it flowers in early summer. There is a form called ‘Alba’ which seeds are true to the parent, which are white flowers. The wild species has lavender flowers.
It is going to be happiest where it’s moist, and it will suffer where it’s dry. In its native geography, it establishes itself very well as colonies – but only where it’s moist and/or cooler in the summers. If cultivating in a warmer climate, it is suggested to keep the soil moisture fairly high.
It is native to grasslands but also to the forest edge – i.e., it will tolerate part shade just fine, though it won’t be quite as spectacular as in full sun.
Growing from Seed
Seeds are known to have a non-deep physiological dormancy, which is very common for Lamiaceae (Mint) plants such as this. Freshly harvested seeds must be cold stratified for 4 weeks – and it’s suggested to do this very cold, around 1.5C (~35F) (Abdalla and McKelvie, 1980). The back, bottom shelf of the fridge (or wherever the lettuce freezes) is a wise choice. Do this for 4 weeks. Seeds must be imbibed (kept somewhat moist) during cold stratification for it to be effective. Dry cold stratification is not very effective (Liu et al, 2011).
Seeds should then be sown around room temperature but do not bury them as they need light to germinate. They should emerge in about a week’s time. Keep them well watered. They will grow quite large if given sufficient nitrogen.
References
Abdalla ST, McKelvie AD. The interaction of chilling and gibberellic acid on the germination of seeds of ornamental plants. Seed Science and Technology. 1980; 8(2): 139-144
Basalaeva IV. Germination dynamics of Polemonium caeruleum L. seeds depending on storage conditions. Trudy Kuban. State Agrar. Univ. 2022; 98:41–45.
Baskin CC, Baskin JM. Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Second Edition. 2014. Academic Press: San Diego, California
Broekhuis R. Rob’s Plants [Website]. URL Available at: www.robsplants.com
Deno N. First Supplement to the Second Edition of Seed Germination Theory and Practice. 1996. Self-Published. Available online by the United States Department of Agriculture at http://naldc.nal.usda.gov/catalog/41279
Deno N. Second Supplement to Seed Germination Theory and Practice. 1998. Self-Published. Available online by the United States Department of Agriculture at http://naldc.nal.usda.gov/catalog/41277
Deno N. Seed Germination Theory and Practice. Second Edition. 1993. Self-Published. Available online by the United States Department of Agriculture at http://naldc.nal.usda.gov/catalog/41278
Gudyniene V, Juzenas S, Stukonis V, Mildaziene V, Ivankov A, Norkeviciene E. Comparing non-thermal plasma and Cold Stratification: which pre-sowing treatment benefits wild plant emergence?. Plants. 2023 Sep 10;12(18):3220.
Liu K, Baskin JM, Baskin CC, Bu H, Liu M, Liu W, Du G. Effect of storage conditions on germination of seeds of 489 species from high elevation grasslands of the eastern Tibet Plateau and some implications for climate change. American Journal of Botany. 2011 Jan;98(1):12-9.
Pigott CD. Polemonium Caeruleum L. Journal of Ecology. 1958 Jul 1;46(2):507-25.