Well in answer to my own question Petunia patagonica is apparently a warm germinator just like it's non hardy brethren. I sowed two of the seed on peat pellets the way I often sow seeds of tiny seed. I take a plastic shoe box or similar, put the pellets in, pour in boiling water and slap the lid on so the whole mess sterilizes, more or less. Works like charm for fern spores, ramonda etc. After I've sown the seed I put the box under lights inside. The two petunia seed germinated in about a week with this treatment. I now plan to move the other pot in from the greenhouse. I don't think I'll keep the newly germinating seed in long because it's probably too warm long term but at least I seem to have conquered the germination hurdle.
