Perennial seed propagation isn’t overly tricky. You just have to follow a few simple guidelines.
The first is to understand that the fancy modern hybrids you see in gardens (like yellow coneflower) do not come true from seed.
Plants of individual species (the wild versions) are different – seed will work but generally speaking, the modern (heavily advertised) plants are not grown from seed but from tissue culture.
Modern plant propagation is heavily concentrated on tissue culture – producing baby plants in test tubes. A 100 square feet of laboratory can produce many more plants in a year than a 100 acre farm. It’s economics.
Seed germinates because hormones within the seedpod start to work to initiate germination or stop working to delay germination (or both)
The trigger points for these hormonal changes are currently thought to be two temperatures – 40F and 70F.
And the exposure time has been worked out to be 90 days at either of these temperatures.
This means that seed either germinates at 40F (e.g. primula) or 70F (e.g. hollyhock)
What about dormant perennial seeds?
Ah dormancy. Here’s where there’s been all kinds of information rolling around the gardening world. Dr. N. Deno established that ending dormancy in seeds is a function of time and temperature and that there were several regimes for achieving germination in the bulk of perennial plants. To make it simpler – I’ll use the temperature numbers 40F and 70F
70 – some seeds such as hollyhock germinate within two weeks if put in damp soil at 70F
40 – some seeds such as primula will generally germinate at 40F (we call these cold germinators) much better than at 70F
40-70 some seeds like to have 90 days at 40F and then moved to 70F. They will usually germinate within the second 90 days.
70-40 a few rather rare seeds will germinate if kept warm for 90 days and then chilled to 40F
How do you know which to use?
Darn good question. Sometimes it is an experience thing. You can also purchase download Dr. Deno’s book listing over 1000 seeds and their requirements from his experiments.
If in doubt – go with half the seed at 70F and the other half at 40-70.
If you only want to try one – try 40-70.
In practical terms, if a seed doesn’t germinate the first sequence, then you can repeat the 40-70 series in the refrigerator. The second time through, you’ll get a few seedlings. But after that, the seeds are likely dead. And this is true more times than you might imagine. I only do my seeds one time – they germinate when they’re supposed to or I throw them away.
There is no need to freeze seed – that kills more seed than it saves. There is very little need to file, scratch or otherwise knick seed coats of perennial seed as they seem to do very well if given the right temperature and length of time.
If the seed is going into a 40-70 regime (90 days at 40F and 90 days at 70F) then I get a baggie and put some damp vermiculite into it. Damp vermiculite means damp – not soaking and certainly with no excess moisture clouding up the baggie. A handful of vermiculite is fine, you don’t require a lot. The objective is to provide a reservoir of humidity, not water or growing medium.
Put the seed in the baggie along with a tag (write the tag with a pen that won’t fade, and is waterproof.)
Put the baggie into the crisper of the refrigerator. Let it sit there for 90 days. Check it every month for germinating seeds (some will start out of season and out of temperature) and for any signs of mold (Remove if molding and sow immediately into sterile soil – treat with a damping-off spray.
After 90 days, sow the seed into a flower pot and keep the soil temperature at 70F using a heat mat. This will germinate seeds quite quickly.
The rough and ready outdoor system.
Take an old 1-gallon container from the nursery pot pile (roughly a 6-inch pot). Cut off the bottom.
Sink the pot in the soil so only the rim is showing and the garden soil is filling the pot
Pour an entire kettle of boiling water (slowly) over the soil in the pot. This will kill off weed seeds and pathogens.
Sow seed – barely cover seed and leave alone all winter to germinate naturally next spring.
All seed flats or pots should be labeled with waterproof marker or pencil so you’ll know what is germinating.
When I water my seedling flats, I always use warm water.
Four True Leaves?
When the seedlings have 4 true leaves, transplant into a small pot and grow until all danger of frost is over.
At this point, they are treated as any other transplant with watering and feeding regularly.
Baby them in the garden (water daily) until they are over their transplant shock and starting to grow.