Thalictrum rochebrunianum

Growing from Seed

There are several important requirements that must be met in order to propagate Thalictrum rochebrunianum from seed.

First, you must use fresh seed; commercial seed is fine, but it must be less than a year old. In other words, from the most recent harvest. Like most Ranunculaceae plants, seeds of this species are not long lived. Ideally, you may want to purchase two plants and then harvest your own seeds. I have harvested seeds at four different times in the year – and only seeds harvested after mid-October were viable (I live in Victoria, British Columbia, Canada, which is a Zone 9b). Seeds should be harvested as they’re falling off the plant – and if you try and grab them off the mother plant they’ll easily come off without much effort. This is the first and most important factor in propagating from seed. (Also, after you harvest seeds, dry them out for 2 weeks at room temperature and then place them dry in a fridge (never freezer) until you start cold stratification. This cold dry storage will help preserve the seeds until you’re ready.)

To grow from seed, you must cold stratify seeds for at least 8 weeks, but preferably 12 weeks (3 months). To do so, wrap the seeds in a moist paper towel or cloth and then place these inside a thin plastic bag – and pop this in the fridge. Never the freezer. Change the paper towel or cloth after 6 weeks if needed. After this, you need to sow the seeds when it’s cool (neither cold nor hot), preferably somewhere around 15C (60F) during the day and colder at night. (See below for a proposed calendar.) Seeds prefer to germinate around 15C (60F) (Lee et al, 2015). You should cover the seed lightly with vermiculite or perlite, but not too deep. Provide a humidity dome.

Seeds of Thalictrum rochebrunianum have a special kind of dormancy called non-deep simple morphophysiological dormancy and which means that, among other things, the baby embryos inside the seeds are not fully developed when the seeds are ripe. After their physiological dormancy is broken with 8-12 weeks of cold stratification (winter), their embryos will mature in the spring. When seeds are sown after cold strat, this is when the embryos are growing. The gardener must be patient, as seeds may need 2 to 3 weeks to emerge at this point.

Do not use a heat mat, as seeds won’t germinate above 30C (~90F). Another important criteria is to avoid using bright grow lights. Germination is inhibited by bright light (Cho et al, 2016), and dim light should be used; or no lights at all. Certainly seed trays should not be exposed to direct sunlight.

Seedlings will emerge in 2 to 3 weeks, and the seed coats will look like little hats on top of the emerging seedlings. Seedlings will need potting up to 2” cells around Day 45, and then planted outside (or potted up again) around Day 90.

Another important (very important) thing to remember about all Ranunculaceae seedlings is that you must not bury the crown or expose the crown. The crown is the part of the plant that is between the stems and the roots – and it has to remain at ground level, neither buried nor too high above the ground. If not done correctly, seedlings will suffer and may die. This is true for most Ranunculaceae plants. Plants may flower in their first year, but likely not until their second year.

If planting outside on May 19th (long weekend fun weekend for gardeners), here is the timeline you must follow. Harvest seeds Oct 30th (thereabouts) and start cold stratification right away – right into the fridge with moist paper towel. That is 3 months long. After this, sow the seeds late January, and by mid-February they will have germinated. Pot up to 2” cells in early April, and by mid-May you’ll be planting them in your garden.

If you search the history in our group, you can see a lot of posts where I harvested seeds and propagated these in 2024-2025.