Greetings! I enjoy your photos of CA native plants and pollinators.
I tried to grow matilija poppies from seed in front of my(socal) apartment. The seed packet said to place them in sawdust and start a small fire. I did not do that. Nothing grew. Do you think the fire was really essential for germination, or is my heavy clay soil the dream killer? I am willing to try again as an arsonist, but my attempts to amend the clay have accomplished very little; (imagine mixing cement with gorilla glue instead of water and you'll have something similar to my clay.)
Hello! I’m happy you’ve been enjoying the blog.
For Mantilija Poppies, fire is essential for germination. Mantilija Poppies, Bush Poppies, and Fire Poppies are all fire following species, their seeds receive cues from the heat and chemical signals of smoke to germinate. This is why in areas touched by fire you will see an explosion in germination of these plants. Their seeds can remain dormant for decades or even centuries in the soil until a fire sweeps through the region (which is why the regular cultural burning practices of local California Indigenous communities are so important to maintaining plant health here.)
I have been collecting and storing Mantilija Poppy seeds but have yet to try to grow some on my own, so take my advice with a grain of salt. You could use the fire and sawdust method for them, but at the Arb they usually get them to germinate using liquid smoke. Yes, liquid smoke as in the bottle of smoke flavoring you can buy for barbecued meat at the grocery store for a few bucks. Liquid smoke is made by condensing actual smoke from burnt wood into a fluid, so it has all the good chemicals from actual fires that trigger germination. Buy a bottle of it, spray it over the soil you are planting the poppies in and see what comes up. The liquid smoke method seems to work effectively on some of the hardest fire following plant seeds to germinate.
Anecdotally, I have also heard that soaking the seeds in rubbing alcohol for 15 minutes can work just as well as liquid smoke. Rubbing alcohol, much like smoke and fire, works to weaken the seed’s outer coat and ease the process of germination. However I haven’t actually seen this method used, and only can vouch for the success of the liquid smoke method in producing a decent amount of seedlings. If I were you, I would get creative and do some experimentation…maybe try the alcohol method, the smoke method, the fire and sawdust method, a combination of alcohol soaking + liquid smoke with four different groups of seeds and see which method(s) work best to ensure germination.
Once the seeds are germinated, I doubt your clay soil will be a problem. Heavy clay soils are found across much of the plant’s range. When full grown the Mantilija Poppy spreads by rhizomes underground, meaning that it will spread out and get taller and bushier as it matures. Some gardeners and botanists call it an “aggressive spreader” or “weedy,” but I prefer to see the Mantilija Poppy as a plant with great resiliency that isn't afraid to take up space. If you have space in front of your apartment for the seedlings to go directly into the ground, they will likely grow fast and get large in the span of 2-3 years, especially if they are in direct sunlight.
Best of luck growing these special plants, and I hope this advice helps! Keep me posted with your results if possible.