The ammonia doesn't sound good, maybe wash the seed by soaking it in a 5% bleach to water solution for 5 minutes, if they haven't already sprouted, then maybe sow them and hope for the best. I have tried 2 varieties of Opuntia recently, one lot did ok, the other I'm still waiting on. Scarification is a simple process, and generally it makes a significant positive difference on any hard coated seed. For both Opuntia's I used a fine grade of sand paper, nail file would do and filed away one edge of the side of the seed. I think you just want to remove enough of the seed coat to allow moisture to penetrate, sort of mimicking digestion by an animal. So I took maybe a 10th of one edge away. Check it with a magnifying glass, you just barely want to see the inside seed. You could gently wash a few of the sown seeds free, if no signs of germination, try scarifying them

Potted Cordylines over here are on sale for around £5 each for a decent plant of say 2ft in height, once in the ground they romp away and look very similar to a 'proper palm'. A tree company a few miles from where I live sells mature Jelly Palms at £699!! as well as Dracaenas, Agaves and Phormiums and other cold hardy palms and exotics. Tree ferns are now 'the UK in thing to grow' and can also be found in large DIY stores locally. Other 'true palms' such as Jelly and Chinese Windmills can be seen in London as the city areas create a micro-climate that provide good conditions for them. The Edinburgh palms are probably growing at the worlds most northerly limit according to what I've just read. Cordylines are also known as Torbay Palms in the UK and have been grown for decades in the south coastal towns around Torquay, and in many others, so much so it has been adopted as the tourist symbol for the Torbay area. Canary Isl palms also grow there. As I said, in almost every place here you will find a Cordline growing somewhere and maybe other true palms if you are lucky. Gill Here is a link that might be useful: palms in Scotland's Logan Gdns.

Hey, Alison, nothing to do with the garden show but don't you love the name of the road? Bells Line of Road??? huh?? I work for company that sub-contracts to Optus (amongst others) for their messaging service and directories and I remember the first time someone told me that road, I thought for sure they had it wrong. weird, huh?

I seem to recall reading in a classic book on NZ plants (Laing & Blackwell, which I don't own now), this anecdote about Cordyline australis: when early NZ settlers were carving out the clearings for their small farms they had a particular problem with the NZ cabbage tree. When they chopped into them with their axes, every chip that flew away and landed on the moist ground soon sprouted and took root, making a new plant. I suspect this would only have happened under a particular regime of temperature, rainfall and humidity.