Published by Brian Wagner on 10/29/25 in “Growing Flowers from Seed.”
Primula sieboldii (commoly called Siebold’s primula) is a quiet but marvelous spectacle, growing in the moist riverbeds and forest edges of southern China, Korea and Japan. Flowering in early spring, it is one of the few Primulas fully adapted for the shade garden. Its flowers are lilac, cream or lavender, and they’re often fringed in texture. Hardy to Zone 4, Siebold’s Primula is a choice perennial.
It is a lover of all things moist, and will be quite happy with seasonally soggy soil. It will not complain with periodic flooding (hello Monty Don) – and it is often observed colonizing a flood plain in its native geography. These are also very long-lived plants and will provide many years of quiet beauty.
Growing from Seed
These are tricky. Of all the primulas, these are perhaps some of the hardest to grow from seed. But, it is worth the reward. They have an intermediate physiological dormancy – which is deeper than the non-deep variety, but not quite as deep as the ‘deep PD’ level.
Fresh seeds are always recommended, but if all you have is dried seeds, then dried seeds it is. To grow from seed, you should warm stratify and then cold stratify. The logic works for this type of dormancy (intermediate PD), as the warm phase can reduce the length of time during the cold phase. To warm stratify, soak the seeds in a 1:10 bleach solution for 15 minutes, and then rinse thoroughly. This will help prevent fungus from growing on the seeds during the warm stratification period. Wrap the seeds in a moist paper towel, place in a thin plastic bag – and place on a north window sill where it gets room temperature plus ambient indirect light. Never keep in the sun though or the seeds can cook and get pushed into a secondary dormancy.
Do the warm stratification for 6 weeks, and then transfer this to the fridge for a whopping 4 months. Some studies have even used 6 months, but that shouldn’t be required if the warm stratification part is done first. Also, keep in the coldest part of your fridge – at the very back, and at the very bottom. Ideally you want around 2C (35F), and if you can crank your fridge down this winter then Bob’s your uncle. These super cold temps for stratification are usually not required, but published studies on this species show a benefit.
The cold stratification should last 4 months. After this, sow the seeds and keep them around 15C (60F) during the day, and if possible down to around 10C (50F) at night. The night/day difference in temperatures has been shown to improve germination for this species. Also, seeds need light to germinate – which means only sowing them on the surface (do not cover), and only use dim light. Seedlings should emerge in about 2 weeks, but be patient if it takes a bit longer.
References
Baskin CC, Baskin JM. Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Second Edition. 2014. Academic Press: San Diego, California
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
Shin Un-Seob, Lee Da-Hyun, Na Chae-Sun. Storage characteristics of Primula sieboldii E. Morren seeds. Proceedings of the Korean Society for Horticultural Science Conference. May 2021: 112–113.
Song JS, Lee JS. Dormancy and germination characteristics of seed and plant of Primula sieboldi. Journal-Korean Society for Horticultural Science. 2002;43(1):91-4.
Song JS. Dormancy breaking of seed and plant, and flowering physiology of Primula sieboldii native to Korea (Doctoral dissertation, Ph. D. Thesis University of Seoul).
Thompson PA. Effects of temperature, chilling and treatment with gibberellins on the germination of Primula species. J Hort Sci. 1970; 45: 175-85.
Washitani I, Kabaya H. Germination responses to temperature responsible for the seedling emergence seasonality of Primula sieboldii E. Morren in its natural habitat. Ecological Research. 1988 Apr;3(1):9-20.
Washitani I, Masuda M. A comparative study of the germination characteristics of seeds from a moist tall grassland community. Functional Ecology. 1990 Jan 1:543-57.