Growing plants from seed can be very satisfying, but most seeds have special requirements for germination in one form or another. It may be as simple as providing warmth and moisture, simulating spring and signalling the embryos inside the seeds to grow. Many seeds from temperate climates require a period of cold stratification before they will germinate under warmer, more spring-like conditions. Other seeds have hard, impenetrable seed coats or contain chemicals that inhibit germination. These have to be worn away, often by passing through the digestive tracts of animals, or going through multiple seasons until the seed coats have weathered, or the chemicals have broken down. These various types of dormancy help prevent the seeds from germinating until conditions are favorable. This may be the coming of spring, or it may be hitching a ride in a birds stomach to an area away from the parent plant, to help prevent competition.
The form of dormancy I'll be writing about today, and one of the most entertaining to overcome, is that of fire-adapted plants. Adult plants may survive fires in various ways, from succulent, water-filled leaves to thick, fire-resistant bark or underground structures called lignotubers, from which new shoots can emerge after a fire burns off the existing shoots. Many plants from regions of the world adapted to fire have seeds that don't germinate until after a fire. In this way, even if the adult plants are killed, the population will continue via the resulting seedlings. Many Californian, Australian and South African plants germinate better after a fire. Research has been done to investigate this phenomenon, pinpointing exactly what about the fire increases the germination. The heat of the flames does provide some mechanical scarification, breaking down hard seed coats, but the part that has the most significant effect is actually from the chemicals produced by the charred plant material and smoke. Various treatments have been developed to utilize smoke for seed germination. You can purchase liquid smoke or smoke paper from certain horticultural supply or seed companies (liquid smoke from the grocery store, for barbecues, is supposed to work, too). You can find all sorts of DIY smoke treatments on youtube.com, like making your own smoked perlite or vermiculite, or "fire water" (not the kind you'd drink).
You can also do things the old fashion way and simply burn some plant matter on top of a pot of seeds. This is the most exiting method, and something I finally tried on some Actostaphylos seeds I received from plantswoman, Kate Bryant. The parent plants are Arctostaphylos pajaroensis 'Warren Roberts' and what might be Arctostaphylos hispida. Given that they are growing side by side, there might be some interesting hybrid seedlings in the mix.
So how did I go about it? First, I collected some dead plant material, mostly pine needles and other California native plant material from work. Pine needles burn easily, and I thought using west coast natives would provide a better mix of chemicals for Arctostaphylos specifically, even if the species used aren't from exactly the same region as the Arctostaphylos seeds I had.
So, once the fire is going, you simply let it burn out, water everything in, and then treat the seeds like any other. Mine are currently in the greenhouse, which is being kept cool enough for the winter that these likely won't germinate until spring. Seeds do involve a lot of waiting, don't they?
I had way more material than I needed for just those two little pots, so I burned most of the rest and then soaked the charred material in a bucket of water. I then collected the resulting "fire water" or "smoke water" to use later. I took most of it in to work to use on some of the Arctostaphylos seeds there, as a comparison to the smoke-treated paper we have for the same purpose. In both cases, I added either smoke water or the smoke paper plus plain water to the seeds and soaked them for about 24 hours. Hoping to see lots of germination in spring!
Frankly, even though the thought of flambeing your seeds is more entertaining, I think I like soaking them in smoke water better. In the fire treatment, most of the smoke floats up and away from the seeds, though the charred material left over the seeds should continue to provide the same chemicals, like a slow-release fertilizer. Also, the material I used was hard to keep within the rim of the pot. Making your own fire water still lets you get your pyro on, but things are a little more manageable, and I think soaking in the smoke water provides a more thorough treatment for the seeds.
Above all, if I try this again, I'll definitely remember to collect my material to burn before it rains!