A 2 foot wide, 8 foot long path in a working, raised vegetable garden is not going to be very comfortable to use. Lined by blackberry that will have to be tied in place to keep them off the path will make things worse. If you have the room, make the paths wider.

I have to assume that the blackberries will be up on trellises. If not, they'll just drape themselves all over your 2' path, and you won't have a path anymore. That being the case, and the blackberries being mostly vertical, it seems like shadowing is going to be hard to avoid. You can decide how tall you're going to let the blackberries get. But untrimmed, they'll get really tall, and the shadows will be pretty large.

Do you have room around all of the beds to get a wheelbarrow in there so you can add soil/compost?

I've found that if possible, at least a 3' path is best.

If you are saying the rows will run north and south - so that the sun shines up each row at it moves across the sky - then the blackberries will not be shading anything else for most of the day anyway. Which is of course the purpose of having rows run north and south instead of east and west in the first place, regardless of what specific crops (and plant heights) are involved.

Not so. If the blackberries are tall, and the sun is in the east, it'll shade a bed in the west, and vice versa. How badly it shades depends on how tall the blackberries are, and how far away the other bed is. If, as suggested, you keep the N-S trellised blackberries pruned to a height of four feet, a bed four feet east or west of the blackberries will get the better part of a full day of sun. A bed right under the blackberries will get exactly half a day of sun.

You appear to be talking about when rows are run east and west. Running rows north and south assures everything is reached by the sun shining up the rows during the course of the day, as it moves across from east to west.

What is your reason for building raised beds instead of having them at the ground level? Do you have a drainage problem?

As for the blackberry bed as well as the paths I would make them 3' wide. Especially 2' wide bed for the blackberries is definitely too narrow.

Running blackberry trellises north and south is a wall running that direction. If you are on the east side of that wall, near the wall, you get no afternoon sun, because the wall is shading it. If you're on the west side of the wall, near the wall, you get no morning sun, because the wall is shading it. The row of blackberries itself gets loads of morning and afternoon sun. It's what is adjacent to that row, in neighboring beds, that we're talking about here. Presumably what is in those beds is nowhere near as tall as the blackberries. A bed a few feet away from a six-foot tall blackberry trellis running north-south will get sunlight only for about half the day, no matter which side it is on. North-south rows offers no magic here when it comes to intercepting sunlight.

It's not hard to work out the exact shadow pattern. It'll depend on the height of the blackberry trellis, and to some extent the latitude.

It depends on orientation and how you prune them, but I think the blackberries would cast shadow at such a close distance. Mine grow like monsters and I need to keep cutting them back all season long. I would also be concerned about the blackberries invading everything... mine try to send up new shoots in every direction.

Would the roots be contained better if they were in a raised bed?

@Gargamel That's a good question...I wonder that too.

@windberry zone5a BCCanada I can plant the blackberries in the ground. I originally thought they would be more manageable in a raised bed if the path next to the bed was only 2'.

Blackberries can only be manageable with ample room around them and by trellising them. I have Triple Crown in the ground with a 2' path and will be trellising them this season and giving them 4' paths. They are UNRULY by nature, give them space and both you and the plants will be happier.

Although there is always the possibility of caneberries running around like bamboo, blackberry varieties generally do not. The rare sprout that comes up at a distance can be easily shovel-pruned. Red raspberries run rampantly, and those out of the row are often mowed. Blackberries do not mind damp ground; raspberries do better in a raised bed. Do not allow your blackberry canes to arch over and touch the ground late in the season; these will take root.

If you do not have a drainage problem I would recommend forgetting about the raised beds. Soil in raised beds drains very quickly what is not what blackberries or vegetables like. It also gets very warm very quickly in hot weather what is not good for the roots. My garden is completely flat. I have a very good drainage and very hot and dry summers, I can't imagine how it would look if I had raised beds, probably disaster. You don't say what type of blackberry you are going to plant. As Anna above I have a Triple Crown. I planted only one plant in the 8' x 6' bed. It occupies the whole bed by itself. After several years though I had blackberry plants sprouting everywhere from the underground runners-roots in a radius of 20'.

At the other extreme, I have grown ground-level caneberries for 25 years, including Triple Crown, and have to shovel-prune two strays per year on average.