You can either plant some trees, such as birch, griselinia or olearia that will quickly grow(with watering and feeding) or plant some climber such as Clematis montana or Russian vine or Virginia creeper that will clamber all over your side of the trees.
My neighbour has 6 conifers which back onto a part of my garden. They are about 20ft tall and he will not prune them. I don’t mind the height too much but the trunks are bare on my side. What can I grow in front of them to mask them please ! I recently saw someone building a bank of soil on tv and planting into that to make their plants taller. Would this be an idea ?
It would not be a great idea, bceause plants growth quite fast and quickly make the height that you would so painstakingly make with a mound of soil.