It's not only the winter rains that might be causing trouble. I doubt they are happy outside all winter with that amount of cold. Unless in some microclimate, they are only rated to zone 10 and various sites dispute even that. They just will not tolerate temps as low as 32F - and you can get colder than that - for long at all.

FWIW, I grew this plant in amended cactus mix in a container for years and any broken bits just got shoved into the soil next to the mother plant and rooted fine. But I left it out too late one year and it got too cold for it overnight and that was the end of that!

This might be a plant that will need to come inside for the winter in your climate if you expect to have long term success.

@gardengal48 Yes Firesticks in particular seems to want zone 10a or higher. I have tried shoving cuts into the soil of the mother plant, and even after three months no growth....

Regarding your plant that rotted one Winter, was that being kept out of the rain? Cold alone rotted it?

Cold alone! And just over night. I have a sheltered area where I stage my houseplants during the summer months that protects them from rain and too much sun. But I push the bringing inside date out as far as I can as even with gro lites in winter, it is too dark inside

Stush taught me: Euphorbia and cactus type plants can be rooted in pure Grani Grit- better than perlite because it is heavy enough to hold the cutting secure- Just put your cutting into the grit in a pot and only occasionally spritz with a spray bottle and only then when the cutting looks to be parched. Keep out of direct sun, You do realize the sap from Firestick is very toxic?

@sans2014 I would use pumice rather than granigrit, as it is heavier than perlite and cactus/euphorbia grow roots really well in it

For Firesticks specifically, how long is it taking you to root them in the shade?

I know about the sap on Firesticks (and most Euphorbia).