A couple of months ago I took 2 cuttings from SP growing in my garden. I let the cuts (on the cuttings) callus over, stuck them in a loose mix consisting largly of perlite and placed the pots next to a glass door.

Some 2-3 weeks ago I noticed the cacti had started growing, which was a sign they had produced roots. The roots, however, are still very small and few. Now, I like to put my cacti outside (and eventually plant them in the ground) as soon as possible to avoid etiolation. The room is heated, but the light levels at this time of year are poor, which causes the cacti to grow and etiolate.

If I put them outside they'll stop growing (or at least slow down) until it warms up, which would prevent etiolation. However, their root systems are still very small and I'm worried they might rot in our wet, dark winter.

What would you suggest?

Another option is to put them in an unheated outbuilding by a window, which would keep them cool and dry.

Your last sentence is your best option. Limited or no water, cool well-lit area but not too much direct light. At this stage of root development I've burned cacti by putting them under lights, in an attempt to avoid etiolation, and I've also burned them by putting them outside in direct sunlight before they'd fully come out of dormancy.

Thanks. I'm not so much concerned about burning them (I've never had SP sun-burn) as I am about them rotting in the damp weather when the undeveloped root systems can't take up much water from the growing medium. However, the growing medium is very free draining and the pots are small so maybe my concerns are unfounded.

Another potential problem is the slugs, which like to nibble on my cacti when it's wet and the plants don't get much sun to dry them.

The problem with the outbuilding is it's quite full and they might get knocked over. I'll keep them outside for now and maybe move them to the outbuilding when the weather warrants it.