Late-flowering peyote cactus

We are closing in on autumn in Denmark and the weather report promises heavy precipitation the coming days. Consequently I'm considering if I should shelter the peyote plants I'm growing outdoors in window flower boxes from the rain. Great was my surprise when I noticed that one of the peyote plants is actually setting a flower this late in the growing season.


Late-flowering peyote cactus

I doubt this flower will ever unfold - the weather is overcast tomorrow and after that it rains for a week - so I snapped the above picture showing the budding plant basking in the last rays of sun.

... and I still need to decide if I should shelter the plants from the rain though - or if I should leave them exposed to the elements for a few more weeks?