Yes it would quite dramatically impact the plants you're growing there. The area is west facing, which means afternoon sun only, some of the plants you're growing are sun lovers. If you put a pergola there and grow climbers up, what's beneath will be in shade even when the sun is on the area. Pergolas are best placed in the sunniest part of a garden, that is, preferably south facing, where you may find excluding hot sun a benefit rather than a negative.

Agree with Bamboo and, in any case, your fence does not have the height or strength to support a pergola.

Here in Moray we consider that everywhere in the garden is 'part-shade' because of the latitude that we live in. Caithness will be even 'shadier' so your plants will need all the light that they can get.

Agree with MG's comment about the height of the fence but would also question why you would build a pergola over a bed/border. If you want something for climbing plants you would be much better with posts with rope swags. A pergola is really something to provide a shady place to sit.

Yes, a pergola does make an attractive feature, but would not work well over a border as others have said. The height of the fence is immaterial, but you could put a run of trellis above it. Our pergola is a great place to sit, and is supported by 5 fence posts with trellis at the side . last page of my photos if you fancy a look?!

Sheila, Bainliam is talking about a lean-to pergola attached to the fence, so the fence height fixes one edge of the pergola.

I take your point, Urbanite - Bainliam would need to add height to his fence (with trellis perhaps?). But the fence itself doesn't need to support the pergola.

It would need something more than trellis to support the weight of the pergola in the top picture. It's bolted to a wall for a reason

Exactly Urbanite! Given Bulba's comment that the last thing you need in Caithness is shade I would suggest that Bainliam has a rethink...