A trellis seems to make a nice neat blackberry rows for smaller plantings. For larger plantings, I’m of the opinion that trellises are a waste of labor.
We planted Triple Crown, Navaho, and Apache without a trellis in 2012. Here is an old pic, but the rows still look the same.
After all these years, we are starting to get more orange rust in the planting. The rows are about 8’ wide with 7’ aisleways. It’s a bit tricky reaching to the middle of the rows (customers have to wade into the blackberries to pick that fruit). The blackberry rows could be kept narrower, but my 8’ wide seems to work OK.
We don’t prune out old canes. We do tip the growing primocanes to encourage lateral growth.
The erect AR varieties Navaho and Apache don’t fill in nearly as well as Triple Crown, so it seems like every year we have to do some significant weeding to those rows