When is the best time to trim back a shrub?

I live in Alberta (zone 3) and I don't know the name of the shrub. It might be an ornamental tree. It has numerous twisted trunks and is about 5 feet tall. It blossoms with gorgeous little pink flowers for about a week or so and then is green the rest of the season. The problemis, is that who ever planted it, planted it too close to the step and it is coming through the rails. It has been poorly trimmed before as it is lop-sided . It is a beautiful shrub but I'm hoping to cut it right back to nothing and hope it grows again and then we can trim it to a nice shape. I'd say it is at least 10-15 yrs old. Any suggestions?

When is the best time to trim back a shrub?
Trim it back immediately AFTER it has bloomed out for the year. You should probably make this a two year project - if you have that much time. If you trim too harshly at one time, the shrub may go into shock. Trim back 1/3 this year and feed with a slow release fertiziler. Snip off new growth during the year. Then next year trim back another 1/2 and feed again. Good luck.