+1 to Phil about growing conditions. Your growing zone is likely a cool one like mine, with a very short growing season. I grow in pots and had a third-year douglah that was as tall as me. I brought it indoors when the weather got too cold and did not do a severe pruning. A really bad aphid attack got to it after that, though, and I let it go. Pubescens can live a very long time, if you have the right conditions (16+ years), and can get both very tall and very wide. But it's unlikely that you'll get them to be as large as they can get if you have to grow in pots. harry's grow log has some pics of his outdoor, in-ground grow if you want to look at them.