Guess you have to wait for warmer weather.
I was at a local artists workshop...he built a pergola as an entrance to his garden.
I think the uprights were cedar..solid. We built a porch where the uprights were metal and then a cedar log was cut in half and wrapped around the metal. It held up part of the house roof...so maybe a precaution?
Anyway, not sure about your tastes...but this artist...hammered spikes into the top of each pole top...and slid colored bottles over...I can't remember ...maybe 3-4 long spikes each pole.
It looked so nice - the sun was hitting the glass perfectly that autumn day.
